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    "slug": "00-theory-of-colours-zur-farbenlehre-full-text",
    "title": "Theory of Colours (Zur Farbenlehre, full text)",
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    "text": "## Theory of Colours (Zur Farbenlehre, full text)\n\n\nGoogle is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the\npublic and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing tliis resource, we liave taken steps to\nprevent abuse by commercial parties, including placing technical restrictions on automated querying.\nWe also ask that you:\n\n+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for\npersonal, non-commercial purposes.\n\n+ Refrain fivm automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine\ntranslation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the\nuse of public domain materials for these purposes and may be able to help.\n\n+ Maintain attributionTht GoogXt \"watermark\" you see on each file is essential for in forming people about this project and helping them find\nadditional materials through Google Book Search. Please do not remove it.\n\n+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just\nbecause we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other\ncountries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of\nany specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner\nanywhere in the world. Copyright infringement liabili^ can be quite severe.\n\nAbout Google Book Search\n\nGoogle's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers\ndiscover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web\n\nat |http: //books .google .com/I\n\nTHEORY OF COLOURS.\n\n\\\n\n/\n\nGOETHE'S\n\nTHEORY OF COLOURS;\n\nTRANSLATED FROM THE GERMAN:\n\nWITH NOTES BY\n\nCHARLES LOCK EASTLAKE, R.A., F.R.S.\n\n6oe|-Kc J»h«v,^, WoLt,c\"'| v<,•■.^\n\n** Cieero Tiuieiatom propria in eoloribut nuei, hinc in alienam mlgrare ejditimaTil.\nCertft Dou alibi natura Gopimint aat m^ore laadYiA opes tna* commeDdaTit. Mntalla.\ngammas, marmora, floraa, aatra, omnia deniqna quB progeoait suia etiam coloriboi dit*\nUnxit; at Tenia debeaior ti qaia in lam nnmerotfi renim tjlri caligaYerit.**\n\nCsLxo CALOAOimn.\n\nLONDON:\n\nJOHN MURRAY, ALBEMARLE STREET.\n\nQC\n¥-95\n\nLONDON:\n\ni*riDt«d by William CcowRt and Sow*,\n\nStamford Strerl.\n\n>^\n\nTO\n\nJEREMIAH HARMAN, Esq.\n\nDear Sir,\n\nI dedicate to you the following translation as a\ntestimony of my sincere gratitude and respect ; in doing so, I\nbut follow the example of Fortius, an Italian writer, who in-\nscribed his translation of Aristotle's Treatise on Colours to one of\nthe Medici.\n\nI have the honour to be.\nDear Sir,\nYour most obliged and obedient Servant,\n\nC. L. EASTLAKE.\n\n■V\n\n)\n\n\\\n\n>\n\\\n\nTHE\n\nTRANSLATOR'S PREFACE.\n\nEnglish writers who have spoken of Goethe's\n** Doctrine of Colours,\"* have generally con-\nfined their remarks to those parts of the work\nin which he has undertaken to account for the\ncolours of the prismatic spectrum, and of re-\nfraction altogether, on principles different from\nthe received theory of Newton. The less ques-\ntionable merits of the treatise consisting of a\nwell- arranged mass of observations and experi-\nments, many of which are important and inter-\nesting, have thus been in a great measure over-\nlooked. The translator, aware of the opposition\nwhich the theoretical views alluded to have met\nwith, intended at first to make a selection of\n\n* '* Farbeulehre\" — in the present translation generally rendered\n\" Theory of Colours.\"\n\n/\n\nVlll TRANSLATOR'S PREFACE.\n\nsuch of the experiments as seem more directly\napplicable to the theory and practice of paint-\ning. Finding, however, that the alterations this\nwould have involved would have been incom-\npatible with a clear and connected view of the\nauthor's statements, he preferred giving the\ntheory itself entire, reflecting, at the same time,\nthat some scientific readers may be curious to\nhear the author speak for himseW even on the\npoints at issue.\n\nIn reviewing the history and progress of his\nopinions and researches, Goethe tells us that he\nfirst submitted his views to the public in two\nshort essays entitled ** Contributions to Optics.\"\nAmong the circumstances which he supposes\nwere unfavourable to him on that occasion, he\nmentions the choice of his title, observing that\nby a reference to optics he must have appeared\nto make pretensions to a knowledge of mathe-\nmatics, a science with which he admits ^e was\nvery imperfectly acquainted. Another cause to\nwhich he attributes the severe treatment he ex-\nperienced, was his having ventured so openly to\nquestion the truth of the established theory :\nbut this last provocation could not be owing to\nmere inadvertence on his part ; indeed the larger\nwork, in which he alludes to these circum-\n\nTRANSLATOR'S PREFACE. IX\n\nStances, is still more remarkable for the violence\nof his objections to the Newtonian doctrine.\n\nThere can be no doubt, however, that much\nof the opposition Goethe met with was to be\nattributed to the manner as well as to the sub-\nstance of his statements. Had he contented\nhimself with merely detailing his experiments\nand showing their application to the laws of\nchromatic harmony, leaving it to others to re-\nconcile them as they could with the pre-estab«\nlished system, or even to doubt in consequence,\nthe truth of some of the Newtonian conclusions,\nhe would have enjoyed the credit he deserved\nfor the accuracy and the utility of his investi-\ngations. As it was, the uncompromising ex-\npression of his convictions only exposed him to\nthe resentment or silent neglect of a great por-\ntion of the scientific world, so that for a time he\ncould not even obtain a fair hearing for the less\nobjectionable or rather highly valuable commu-\nnications contained in his book. A specimen\nof his manner of alluding to the Newtonian\ntheory will be seen in the preface.\n\nIt was quite natural that this spirit should\ncall forth a somewhat vindictive feeling, and\nwith it not a little uncandid as well as unspar-\ning criticism. \" The Doctrine of Colours' met\n\nX TRANSLATOR'S PREFACE.\n\nwith this reception in Germany long before it\nwas noticed in England^ where a milder and\nfairer treatment could hardly be expected, espe-\ncially at a time when, owing perhaps to the\nlimited intercourse with the continent, German\nliterature was far less popular than it is at pre-\nsent. This last fact, it is true, can be of little\nimportance in the present instance, for although\nthe change of opinion with regard to the genius\nof an enlightened nation must be acknowledged\nto be beneficial, it is to be hoped there is no\nfashion in science, and the translator begs to\nstate once for all, that in advocating the ne-\nglected merits of the \"Doctrine of Colours/' he\nis far from undertaking to defend its imputed\nerrors. Sufficient time has, however, now\nelapsed since the publication of this work (in\n1810) to allow a calmer and more candid exami-\nnation of its claims. In this more pleasing task\nGermany has again for some time led the way,\nand many scientific investigators have followed\nup the hints and observations of Goethe with a\ndue acknowledgment of the acuteness of his\nviews.*\n\n* Sixteen years after the appearance of the Farbenlehre, Dr.\nJohannes Miller devoted a portion of his work, '*Zur vergleich-\nenden Physiologic des Gesichtssinnes des Menschen und der\n\nTRANSLATOR'S PREFACE. XI\n\nIt may require more magnanimity in English\nscientific readers to do justice to the merits of\none who was so open and, in many respects,\nit is belieyed, so mistaken an opponent of\nNewton; but it must be admitted that the\nstatements of Goethe contain more useful prin-\nciples in all that relates to harmony of colour\nthan any that have been derived from the esta-\nblished doctrine. It is no derogation of the\nmore important truths of the Newtonian theory\nto say, that the views it contains seldom appear\nin a form calculated for direct application to the\narts. The principle of contrast, so universally\nexhibited in nature, so apparent in the action\nand re-action of the eye itself, is scarcely hinted\nat. The equal pretensions of seven colours, as\n\nThiere,\" to the critical examination of Goethe's theory. In his\nintroductory remarks he expresses himself as follows — *^ For my\nown part I readily acknowledge that I have heen greatly indebted\nto Goethe's treatise, and can truly say that without having studied\nit for some years in connexion with the actual phenomena, the pre-\nsent work would hardly have been undertaken. I have no hesitation\nin confessing more particularly that I have full faith in Goethe's\nstatements, where they are merely descriptive of the phenomena,\nand where the author does not enter into explanations involving\na decision on the great points of controversy.\" The names of\nHegel, Schelling, Seebeck, Steffens, may also be mentioned, and\nmany others might be added, as authorities more or less favourable\nto the Farbenlehre.\n\nXII TRANSLATOR'S PREFACE.\n\nsuch, and the fanciful analogies which ttieir\nassumed proportions could suggest, have rarely\nfound favour with the votaries of taste, — indeed\nthey have long been abandoned even by\nscientific authorities.* And here the trans-\nlator stops : he is quite aware that the defects\nwhich make the Newtonian theory so little\navailable for aesthetic application, are far from\ninvalidating its more important conclusions in\nthe opinion of most scientific men. In carefully\nabstaining therefore from any comparison be-\ntween the two theories in these latter respects,\nhe may still be permitted to advocate the clear-\nness and fulness of Goethe*s experiments. The\nGerman philosopher reduces the colours to their\n\n* \"When Newton attempted to reckon up the rays of light\ndecomposed by the prism,\" says Sir John Leslie, ^*and ventured\nto assign the fieunous number seven^ he was apparently influenced\nby some lurking disposition towards mysticism. If any unpreju-\ndiced person will fairly repeat the experiment, he must soon be\nconvinced that the various coloured spaces which paint the spec-\ntrum slide into each other by indefinite shadings : he may name\nfour or five principal colours, but the subordinate spaces are evi-\ndently so multiplied as to be incapable of enumeration. The\nsame illustrious mathematician, we can hardly doubt, was be-\ntrayed by a passion for analogy, when he imagined that the pri-\nmary colours are distributed over the spectrum after the proportions\nof the diatonic scale of music, since those intermediate spaces have\nreally no precise and defined limits.\" — Treatises on Various\nSubjects of Natural and Chemical Philosophy, p. 59.\n\nmtr\n\nTRANSLATOR'S PREFACE. XUl\n\norigin and simplest elements ; he sees and con-\nstantly bears in mind, and sometimes ably\nelucidates, the phenomena of contrast and gra-\ndation, two principles which may be said to\nmake up the artist's world, and to constitute the\nchief elements of beauty. These hints occur\nmostly in what may be called the scientific part\nof the work.. On the other hand, in the portion\nexpressly devoted to the aesthetic application of\nthe doctrine, the author seems to have made but\nan inadequate use of his own principles.\n\nIn that part of the chapter on chemical co-\nlours which relates to the colours of plants and\nanimals, the same genius and originality which\nwe displayed in the Essays on Morphology, and\nwhich have secured to Goethe undisputed rank\namong the investigators of nature, are frequently\napparent.\n\nBut one of the most interesting features of\nGoethe's theory, although it cannot be a recom-\nmendation in a scientific point of view, is, that\nit contains, undoubtedly with very great im-\nprovements, the general doctrine of the ancients\nand of the Italians at the revival of letters.\nThe translator has endeavoured, in some notes,\nto point out the connexion between this theory\nand the practice of the Italian painters.\n\nXIV TRANSLATOR'S PREFACE.\n\nThe *' Doctrine of Colours,\" as first published\nin 1810, consists of two volumes in 8vo., and\nsixteen plates, with descriptions, in 4to. It is\ndivided into three parts^ a didactic, a contro-\nversial, and an historical part; the present\ntranslation is confined to the first of these, with\nsuch extracts from the other two as seemed\nnecessary, in fairness to the author, to explain\nsome of his statements. The polemical and\nhistorical parts are frequently alluded to in the\npreface and elsewhere in the present work, but\nit has not been thought advisable to omit these\nallusions. No alterations whatever seem to\nhave been made by Goethe in the didactic por-\ntion in later editions, but he subsequently wrote\nan additional chapter on entoptic colours, ex-\npressing his wish that it might be inserted in\nthe theory itself at a particular place which he\npoints out. The form of this additional essay\nis, however, very different from that of the rest\nof the work, and the translator has therefore\nmerely given some extracts from it in the ap-\npendix. The polemical portion has been more\nthan once omitted in later editions.\n\nIn the two first parts the author's statements\nare arranged numerically, in the style of Bacon's\nNatural History. This, we are told, was for the\n\npia^iMwa-«^>— mwvMKBBm\n\nTRANSLATOR'S PREFACE. XV\n\nconvenience of reference; but many passages\nare thus separately numbered which hardly\nseem to have required it. The same arrange-\nment is, however, strictly followed in the trans-\nlation to facilitate a comparison with the original\nwhere it may be desired ; and here the translator\nobserves, that although he has sometimes per-\nmitted himself to make slight alterations^ in\norder to avoid unnecessary repetition, or to\nmake the author's meaning clearer, he feels\nthat an apology may rather be expected from\nhim for having omitted so little. He was scru-\npulous on this point, having once determined to\ntranslate the whole treatise, partly, as before\nstated, from a wish to deal fairly with a con-\ntroversial writer, and partly because many pas-\nsages, not directly bearing on the scientific\nviews, are still characteristic of Goethe. The\nobservations which the translator has ventured\nto add are inserted in the appendix : these ob-\nservations are chiefly confined to such of the\nauthor's opinions and conclusions as have direct\nreference to the arts ; they seldom interfere with\nthe scientific propositions, even where these\nhave been considered most vulnerable.\n\nPREFACE TO THE FIRST EDITION\n\nOF 1810.\n\nIt may naturally be asked whether, in proposing\nto treat of colours, light itself should not first\nengage our attention : to this we briefly and\nfrankly answer that since so much has already\nbeen said on the subject of light, it can hardly\nbe desirable to multiply repetitions by again\ngoing over the same ground.\n\nIndeed, strictly speaking, it is useless to at-\ntempt to express the nature of a thing abstract-\nedly. Effects we can perceive, and a complete\nhistory of those effects would, in fact, sufficiently\ndefine the nature of the thing itself. We should\ntry in vain to describe a man's character, but let\nhis acts be collected and an idea of the character\nwill be presented to us.\n\nThe colours arc acts of light; its active and\npassive modifications : thus considered we may\nexpect from thom some explanat'^ i respecting\nlight ilsel^Colp' ilighr xe, stand\n\nin the |^^^|^ ^ ]]er. but\n\nXVlll PBEFACE TO THE FIRST EDITION.\n\nwe should think of both as belonging to nature\nas a whole^ for it is nature as a whole which\nmanifests itself by their means in an especial\nmanner to the sense of sight.\n\nThe completeness of nature displays itself to\nanother sense in a similar way. Let the eye be\nclosed, let the sense of hearing be excited, and\nfrom the lightest breath to the wildest din, from\nthe simplest sound to the highest harmony,\nfrom the most vehement and impassioned cry\nto the gentlest word of reason, still it is Nature\nthat speaks and manifests her presence, her\npower, her pervading life and the vastness of\nher relations ; so that a blind man to whom the\ninfinite visible is denied^ can still comprehend\nan infinite vitality by means of another organ.\n\nAnd thus as we descend the scale of being,\nNature speaks to other senses — to known, mis-\nunderstood, and unknown senses : so speaks she\nwith herself and to us in a thousand modes. To\nthe attentive observer she is nowhere dead nor\nsilent ; she has even a secret agent in inflexible\nmatter, in a metal, the smallest portions of which\ntell us what is passing in the entire mass. How-\never manifold, complicated, and unintelligible\nthis language may often seem to us, yet its ele-\nments remain ever the same. With light poise\n\n— ■- -^ --— >\"*\n\nPBEFACE TO THE FIRST EDITION. XIX\n\nand counterpoise, Nature oscillates within her\nprescribed limits* yet thus arise all the varieties\nand conditions of the phenomena which are\npresented to us in space and time.\n\nInfinitely various are the means by which we\nbecome acquainted with these general move-\nments and tendencies :. now as a simple repul-\nsion and attraction, now as an upsparkling and\nvanishing light, as undulation in the air, as com-\nmotion in matter, as oxydation and deoxydation ;\nbut always, uniting or separating, the great pur-\npose is found to be to excite and promote exist-\nence in some form or other.\n\nThe observers of nature finding, however,\nthat this poise and counterpoise are respectively\nunequal in effect, have endeavoured to repre-\nsent such a relation in terms. They have every-\nwhere remarked and spoken of a greater and\nlesser principle, an action and resistance, a\ndoing and suffering, an advancing and retiring,\na violent and moderating power; and thus a\nsymbolical language has arisen, which, from\nits close analogy, may be employed as equiva-\nlent to a direct and appropriate terminology.\n\nTo apply these designations, this language of\nNature to the subject we have undertaken ; to\nenrich and amplify this language by meaw9k o^\n\nXX PREFACE TO THE FIRST EDITION.\n\nthe theory of colours and the variety of their\nphenomena, and thus facilitate the communica-\ntion of higher theoretical views, was the prin-\ncipal aim of the present treatise.\n\nThe work itself is divided into three parts.\nThe first contains the outline of a theory of\n\ncolours. In this, the innumerable cases which\n\n•\n\npresent themselves to the observer are collected\nunder certain leading phenomena, according to\nan arrangement which will be explained in the\nIntroduction ; and here it may be remarked, that\nalthough we have adhered throughout to experi-\nment, and throughout considered it as our basis,\nyet the theoretical views which led to the ar-\nrangement alluded to, could not but be stated.\nIt is sometimes unreasonably required by per-\nsons who do not even themselves attend to\nsuch a condition, that experimental information\nshould be submitted without any connecting\ntheory to the reader or scholar, who is himself\nto form his conclusions as he may list. Surely\nthe mere inspection of a subject can profit us\nbut little. Every act of seeing leads to consi-\nderation, consideration to reflection, reflection\nto combination, and thus it may be said that in\nevery attentive look on nature we already theo-\nrise. But in order to guard against the possible\n\nFBEFACE TO THE FIRST EDITION. XXI\n\nabuse of this abstract view, in order that the\npractical deductions we look to should be really\nuseful, we should theorise without forgetting\nthat we are so doing, we should theorise with\nmental self-possession, and, to use a bold word,\nwith irony.\n\nIn the second part* we examine the New-\ntonian theory ; a theory which by its ascend-\nancy and consideration has hitherto impeded a\nfree inquiry into the phenomena of colours. We\ncombat that hypothesis, for although it is no\nlonger found available, it still retains a tradi-\ntional authority in the world. Its real relations\nto its subject will require to be plainly pointed\nout ; the old errors must be cleared away, if the\ntheory of colours is not still to remain in the rear\nof so many other better investigated depart-\nments of natural science. Since, however, this\nsecond part of our work may appear somewhat\ndry as regards its matter, and perhaps too vehe-\nment and excited in its manner, we may here\nbe permitted to introduce a sort of allegory in\na lighter style, as a prelude to that graver por-\ntion, and as some excuse for the earnestness\nalluded to.\n\nWe compare the Newtonian theory of colours\n\n* The Polemical part.\n\nXXii PREFACE TO THE FIB8T EDITION.\n\nto an old castle, which was at first constrocted\nby its architect with youthful precipitation ; it\nwas, however, gradually enlarged and equipped\nby him according to the exigencies of time and\ncircumstances, and moreover was still further\nfortified and secured in consequence of feuds\nand hostile demonstrations.\n\nThe same system was pursued by his succes*\nsors and heirs : their increased wants within,\nthe harassing vigilance of their opponents with-\nout, and various accidents compelled them in\nsome places to build near, in others in con«\nnexion with the fabric, and thus to extend the\noriginal plan.\n\nIt became necessary to connect all these in-\ncongruous parts and additions by the strangest\ngalleries, halls and passages. All damages,\nwhether inflicted by the hand of the enemy or\nthe power of time, were quickly made good. As\noccasion required, they deepened the moats,\nraised the walls, and took care there should be\nno lack of towers, battlements, and embrasures.\nThis care and^ these exertions gave rise to a pre-\njudice in favour of the great importance of the\nfortress, and still upheld that prejudice, although\nthe arts of building and fortification were by\nthis time very much advanced, and people had\n\nPBEFACE TO THE FIBST EDITION. XXUl\n\nlearnt to construct much better dwellings and\ndefences in other cases. But the old castle\nwas chiefly held in honour because it had\nnever been taken, because it had repulsed so\nmany assaults, had baffled so many hostile\noperations, and had always preserved its virgin\nrenown. This renown, this influence lasts even\nnow : it occurs to no one that the old castle is\nbecome uninhabitable. Its great duration, Jts\ncostly construction, are still constantly spoken\nof. Pilgrims wend their way to it ; hasty\nsketches of it are shown in all schools, and it is\nthus recommended to the reverence of suscep*\ntible youth. Meanwhile, the building itself is\nalready abandoned ; its only inmates are a few\ninvalids, who in simple seriousness imagine that\nthey are prepared for war.\n\nThus there is no question here respecting a\ntedious siege or a doubtful war ; so far from it\nwe find this eighth wonder of the world already\nnodding to its fall as a deserted piece of anti*\nquity, and begin at once, without further cere^\nmony, to dismantle it from gable and roof\ndownwards ; that the sun may at last shine into\nthe old nest of rats and owls, and exhibit to the\neye of the wondering traveller that labyrinthine,\nincongruous style of building, with it;^ %c.^\\iVj ^\n\nXXIV PREFACE TO THE FIRST EDITION.\n\nmake-sbift contriyances, the result of accident\nand emergency, its intentional artifice and\nclumsy repairs. Such an inspection will, how-\never, only be possible when wall after wall, arch\nafter arch, is demolished, the rubbish being at\nonce cleared away as well as it can be.\n\nTo effect this, and to level the site where it is\npossible to do so, to arrange the materials thus\nacquired, so that they can be hereafter again\nemployed for a new building, is the arduous\nduty we have undertaken in this Second Part.\nShould we succeed, by a cheerful application of\nall possible ability and dexterity, in razing this\nBastille, and in gaining a free space, it is thus\nby no means intended at once to cover the site\nagain and to encumber it with a new structure ;\nwe propose rather to make use of this area for\nthe purpose of passing in review a pleasing and\nvaried series of illustrative figures.\n\nThe third part is thus devoted to the histo-\nrical account of early inquirers and investiga-\ntors. As we before expressed the opinion that\nthe history of an individual displays his cha-\nracter, so it may here be well affirmed that the\nhistory of science is science itself. We cannot\nclearly be aware of what we possess till we have\nthe means of knowing what others possessed\n\nPREFACE TO THE FIRST EDITION. XXT\n\nbefore us. We cannot really and honestly re-\njoice in the advantages of our own time if we\nknow not how to appreciate the advantages of\nformer periods. But it was impossible to write,\nor even to prepare the way for a history of the\ntheory of colours while the Newtonian theory\nexisted; for no aristocratic presumption has\never looked down on those who were not of its\norder, with such intolerable arrogance as that\nbetrayed by the Newtonian school in deciding\non all that had been done in earlier times and\nall that was done around it. With disgust and\nindignation we find Priestley, in his History of\nOptics, like many before and after him, dating\nthe success of all researches into the world of\ncolours firom the epoch of a decomposed ray\nof light, or what pretended to be so ; looking\ndown with a supercilious air on the ancient and\nless modern inquirers, who, after all, had pro-\nceeded quietly in the right road, and who have\ntransmitted to us observations and thoughts in\ndetail which we can neither arrange better nor\nconceive more justly.\n\nWe have a right to expect from one who pro-\nposes to give the history of any science, that he\ninform us how the phenomena of which it treats\nwere gradually known, and what wa^ vn\\:^\\\\i^^>\n\nXXyi PRSFACJB TO THE FIRST EDITION.\n\nconjectured, assumed, or thought respecting\nthem* To state all this in due connexion is by\nDO means an easy task ; need we say that to\nwrite a history at all is always a hazardous\naffair ; with the most honest intention there is\nalways a danger of being dishonest ; for in such\nan undertaking, a writer tacitly announces at\nthe outset that he means to place some things\nin light, others in shade. The author has«\nnevertheless, long derived pleasure from the\nprosecution of his task : but as it is the in^\ntention only that presents itself to the mind\nas a whole, while the execution is gene-\nrally accomplished portion by portion, he is\ncompelled to admit that instead of a history\nhe furnishes only materials for one. These\nmaterials consist in translations^ extracts, ori*\nginal and borrowed comments, hints, and notes ;\na collection, in short, which, if not answering\nall that is required, has at least the merit of\nhaving been made with earnestness and inte-\nrest. Lastly, such materials, — not altogether\nuntouched it is true, but still not exhausted, — *\nmay be more satisfactory to the reflecting reader\nin the state in which they are, as he can easily\ncombine them according to his own judgment.\nThis third part, containing the history of the\n\nPBSFACB TO THB FIB8T EDITIOH . XXYll\n\nscience, does not» however, thus conclude the\nsubject: a fourth supplementary portion* is\nadded. This contains a recapitulation or revi*\nsion ; with a view to which, chiefly, the para-\ngraphs are headed numerically. In the execu-\ntion of a work of this kidd some things may be\nforgotten, some are of necessity omitted, so as\nnot to distract the attention, some can only be\narrived at as corollaries, and others may require\nto be exemplified and verified : on all these ac-\ncounts, postscripts, additions and corrections\nare indispensable. This part contains, besides,\nsome detached essays ; for example, that on the\natmospheric colours ; for as these are introduced\nin the theory itself without any classification,\nthey are here presented to the mind's eye at\none view^ Again, if this essay invites the reader\nto consult Nature herself, another is intended to\nrecommend the artificial aids of science by cir-\ncumstantially describing the apparatus which\nwill in future be necessar}^ to assist researches\ninto the theory of colours.\nIn conclusion, it only remains to speak of the\n\n* This preface must have heen written before the work was\nfinished, for at the conclusion of the historical part there is only\nan apology for the non-appearance of the supplement here al-\nluded to.\n\nXXVIU PREFACE TO THE FIRST EDITION.\n\nplates which are added at the end of the work ;*\nand here we confess we are reminded of that\nincompleteness and imperfection which the\npresent undertaking has» in common with all\nothers of its class ; for as a good play can be in\nfact only half transmitted to writing, a great\npart of its effect depending on the scene, the\npersonal qualities of the actor, the powers of\nhis voice, the peculiarities of his gestures, and\neven the spirit and favourable humour of the\nspectators; so it is, in a still greater degree,\nwith a book which treats of the appearances of\nnature. To be enjoyed, to be turned to account.\nNature herself must be present to the reader,\neither really, or by the help of a lively imagina-\ntion. Indeed, the author should in such cases\ncommunicate his observations orally, exhibiting\nthe phenomena he describes — as a text, in the\nfirst instance, — partly as they appear to us un-\nsought, partly as they may be presented by\ncontrivance to serve in particular illustration.\nExplanation and description could not then fail\nto produce a lively impression.\n\nThe plates which generally accompany works\nlike the present are thus a most inadequate sub-\n\n* In the present translation the necessary plates accompany\nthe text.\n\nPREFACE TO THE FIRST EDITION. XXIX\n\nstitute for all this; a physical phenomenon\nexhibiting its effects on all sides is not to be\narrested in lines nor denoted by a section. No\none ever dreams of explaining chemical expe-\nriments with figures ; yet it is customary in\nphysical researches nearly allied to these, be-\ncause the object is thus found to be in some\ndegree answered. In many cases, however, such\ndiagrams represent mere notions ; they are sym-\nbolical resources, hieroglyphic modes of com-\nmunication, which by degrees assume the place\nof the phenomena and of Nature herself^ and\nthus rather hinder than promote true know-\nledge. In the present instance we could not\ndispense with plates, but we have endeavoured\n80 to construct them that they may be confi-\ndently referred to for the explanation of the\ndidactic and polemical portions. Some of these\nmay even be considered as forming part of the\napparatus before mentioned.\n\nWe now therefore refer the reader to the\nwork itself; first, only repeating a request\nwhich many an author has already made in\nvain, and which the modern German reader,\nespecially, so seldom grants: —\n\nSi quid novisti rectius istis\nCandidus imperii ; si noD, his utere mecum*\n\nDIRECTIONS FOR PLACING THE PLATES.\n\nPlate 1 to face page\n\n2 ditto\n\n3 ditto\nI ditto\n\nCONTENTS.\n\nPAGE\n\nIntroduction .... xxxyii\n\nPAKT I.\n\nPHYSIOLOGICAL COLOURS.\n\nI. Effects of Light and Darkness on the Eye . 2\n\nII. Effects of Black and White Objecto on the Eye 5\n\nIII. Grey Surfaces and Objects . . 14\n\nIV. Dazzling Colourless Objects . . . 16\n- V. Coloured Objects . . • 20\n\nVI. Coloured Shadows . . . 29\n\nYII. Faint Lighto . . .38\n\nVIII. Subjective Halos . . . . 40\n\nPathological Colours — ^Appendix . . 45\n\nPART II.\n\nPHYSICAL COLOURS.\n\nIX. Dioptrical Colours . • . 59\nX. Dioptrical Colours of the First Class . 60\nXI. Dioptrical Coloiurs of the Seomd Claife— Re-\nfraction . . . • 74\nSubjective Experiments . . .80\nXII. Refraction without the Appearance of Colour ib.\n\nXIII. Conditions of the Appearance of Colour . 81\n\nXIV. Conditions under which the Appearance of Co-\n\nlour increases . .86\n\nXV. Explanation of the foregoing Phenomena • 90\n\nXVI. Decrease of the Appearance of Colour . 100\n\nXVII. Grey Objects displaced by Refraction . .103\n\nXVI 11. Coloured Objects displaced by Refraction . 106\n\nXIX. Achromatism and Hyperchromatism . 118\n\nCONTENTS.\n\nTAOS\n\nXX. Advantages of Subjective Experimenta —\n\nTransition to the Objective\n\n. 123\n\nObjective Experiments\n\n. 125\n\nXXI. Refraction without the Appearance of Colou\n\nr 127\n\nXXI I. Conditions of the Appearance of Colour\n\n. 128\n\nXXIII. Conditions of the Increase of Colour\n\n. 134\n\nXXIV. Explanation of the foregoing Phenomena\n\n. 139\n\nXXV. Decrease of the Appearance of Colour\n\n, 141\n\nXXVI. Grey Objects\n\n. 142\n\nXXVII. Coloured Objects\n\nXXVIII. Achromatism and Hyperchromatism\n\n. 145\n\nXXIX. Combination of Subjective and Objective Ex-\n\nperiments . . ,\n\nXXX. Transition\n\nXXXI. Catoptrical Colours\n\nXXXII. Paroptical Colours\n\nXXXIII. Epoptical Colours\n\nPART III.\n\nCHEMICAL COLOURS.\n\nXXXIV. Chemical Contrast .\n\nXXXV. White . . . .\n\nXXXVI. Black ....\n\nXXXVII. First Excitation of Colour\n\nXXXVIII. Augmentation of Colour\n\nXXXIX. Culmination . . . .\n\nXL. Fluctuation\n\nXLI. Passage through the Whole Scale\n\nXLII. Inversion\n\nXLI II. Fixation . . .\n\nXLIV. Intermixture, Real\n\nXLV. Intermixture, Apparent\n\nXLVI. Communication, Actual\n\nXLVII. Communication, Apparent\n\nXLVIII. Extraction\n\nXLIX. Nomenclature . . . .\n\nCONTENTS. XXXlll\n\nPAQB\n\n^L. Minerals .... 245\n\nLI. Plants . . • . . 247\n\nLI I. Worm?, Insects, Fishes . . 252\n\nLIII. Birds . . . . . 259\n\nLIV. Mammalia and Human Beings . . 262\n\nLV. Physical and Chemical Effects of the Transmission\n\nof Light through Coloured Mediums . . 266\n\nLVI. Chemical Effect in Dioptrical Achromatism . 270\n\nPART IV.\n\nGENEBAL CHARACTERISTICS.\n\nThe Facility with which Colour appears . • 274\n\nThe Definite Nature of Colour • 276\n\nComhination of the Two Principles . . . 277\n\nAugmentation to Red . . . ib.\n\nJunction of the Two Augmented Extremes . . 278\n\nCompleteness the Result of Variety in Colour . .279\n\nHarmony of the Complete State . . 280\nFacility with which Colour may be made to tend either to\n\nthe Plus or Minus side . . .281\n\nEvanescence of Colour . . . . ib.\n\nPermanence of Colour . . . « 282\n\nPART V.\n\nRELATION TO OTHER PURSUITS.\n\nRelation to Philosophy .... 283\n\nRelation to Mathematics • . • . 286\n\nRelation to the Technical Operations of the Dyer • 289\n\nRelation to Physiology and Pathology . 291\n\nRelation to Natural History . 292\n\nRelation to General Physics . . . . 293\n\nRelation to the Theory of Music . . . 298\n\nConcluding Observations on Terminology . . 300\n\nPART VI.\n\nEFFECT OF COLOUR WITH REFERENCE TO MORAL\n\nASSOCIATIONS.\n\nYelloiF . . . . • ^»fe\n\ne\n\nXXXIT CONTENTS.\n\nPAGE\n\nRed-Yellow ....\n\nYellow-Red\n\nBlue .....\n\nRed-Blue ....\n\nBlue-Red ....\n\nRed ... .\n\nib.\n\nGreen . . • • .\n\nCompleteness and Harmony\n\nib.\n\nCharacteristic Combinations .\n\nYellow and Blue\n\nYellow and Red\n\nib.\n\nBlue and Red\n\nib.\n\nYellow-Red and Blue-Red .\n\nCombinations Non-Characteristic .\n\nRelation of the Combinations to Light and Dark\n\nConsiderations derived from the Evidence of Experience\n\nand History\n\niEsthetic Influence\n\nChiaro-Scuro\n\nTendency to Colour\n\nKeeping ....\n\nColouring ....\n\nColour in General Nature\n\nib.\n\nColour of Particular Objects .\n\nCharacteristic Colouring\n\nHarmonious Colouring\n\nGenuine Tone\n\nFalse Tone ....\n\nib.\n\nWeak Colouring\n\nThe Motley ....\n\nDread of Theory\n\nib.\n\nUltimate Aim .\n\nGrounds ....\n\nib.\n\nPigments ....\n\nAllegorical, Symbolical, Mystical Application of Colour\n\nConcluding Observations\n\nOUTLINE\n\nOF A\n\nTHEORY OF COLOURS.\n\n** 8i Ten nostra sunt aut falsa, emnt talia, licet nostra per Titam defen-\ndimus. Post fata nostra pueri qui nunc ludunt nostri judices erunt.\"\n\nt^ 1\n\nINTRODUCTION.\n\nThe desire of knowledge is first stimulated in us\nwhen remarkable phenomena attract our atten-\ntion. In order that this attention be continued,\nit is necessary that we should feel some interest\nin exercising it, and thus by degrees we become\nbetter acquainted with the object of our curi-\nosity. During this process of observation we\nremark at first only a vast variety which presses\nindiscriminately on our view ; we are forced to\nseparate, to distinguish, and again to combine ;\nby which means at last a certain order arises\nwhich admits of being surveyed with more or\nless satisfaction.\n\nTo accomplish this, only in a certain degree,\nin any department, requires an unremitting and\nclose application ; and we find, for this reason,\nthat men prefer substituting a general theore-\ntical view, or some system of explanation, for\nthe facts themselves, instead of taking the trou-\nble to make themselves first acquainted with\ncases in detail and then constructing a whole.\n\nThe attempt to describe and class the phe-\nnomena of colours has been only twice made :\nfirst by Theophrastus,* and in modern times by\n\n* The treatise to which the author alludes is more generally\nascribed to Aristotle. — T.\n\nXXXVlll INTRODUCTION.\n\nBoyle. The pretensions of the present essay\nto the third place will hardly be disputed.\n\nOur historical survey enters into further de-\ntails. Here we merely observe that in the last\ncentury such a classification was not to be\ntliought of, because Newton had based his hypo-\nthesis on a phenomenon exhibited in a compli-\ncated and secondary state ; and to this the other\ncases that forced themselves on the attention\nwere contrived to be referred, when they could\nnot be passed over in silence; just as an astro-\nnomer would do, if from whim he were to place\nthe moon in the centre of our system ; he would\nbe compelled to make the earth, sun, and pla-\nnets revolve round the lesser body, and be forced\nto disguise and gloss over the error of his first\nassumption by ingenious calculations and plau-\nsible statements.\n\nIn our prefatory observations we assumed the\nreader to be acquainted with what was known\nrespecting light ; here we assume the same with\nregard to the eye. We observed that all nature\nmanifests itself by means of colours to the sense\nof sight. We now assert, extraordinary as it\nmay in some degree appear, that the eye sees\nno form, inasmuch as light, shade, and colour\ntogether constitute that which to our vision dis-\ntinguishes object from object, and the parts of\nan object from each other. From these three,\nlight, shade, and colour, we construct the visible\n\nINTRODUCTION. XXxix\n\nvrorld, and thus, at the same time, make paint-\ning possible, an art which has the power of\nproducing on a flat surface a much more perfect\nvisible world than the actual one can be.\n\nThe eye may be said to owe its existence to\nlight, which calls forth, as it were, a sense that\nis akin to itself; the eye, in short, is formed\nwith reference to light, to be fit for the action\nof light ; the light it contains corresponding with\nthe light without.\n\nWe are here reminded of a significant adage\nin constant use with the ancient Ionian school —\n** Like is only known by Like ;\" and again, of\nthe words of an old mystic writer, which may\nbe thus rendered, '' If the eye were not sunny,\nhow could we perceive light? If God's own\nstrength lived not in us, how could we delight\nin Divine things?\" This immediate affinity\nbetween light and the eye will be denied by\nnone; to consider them as identical in sub-\nstance is less easy to comprehend. It will be\nmore intelligible to assert that a dormant\nlight resides in the eye, and that it may be ex-\ncited by the slightest cause from within or from\nwithout. In darkness we can, by an efibrt of\nimagination, call up the brightest images; in\ndreams objects appear to us as in broad day-\nlight; awake, the slightest external action of\nlight is perceptible, and if the organ suffers an\nactual shock, light and colours spring forth.\n\nINTRODUCTION.\n\nHere, however, those who are wont to proceed\naccording to a certain method, may perhaps\nobserve that as yet we have not decidedly ex-\nplained what colour is. This question, like the\ndefinition of light and the eye, we would for the\npresent evade, and would appeal to our inquiry\nitself, where we have circumstantially shown\nhow colour is produced. We have only there-\nfore to repeat that colour is a law of nature in\nrelation with the sense of sight. We must as-\nsume, too, that every one has this sense, that\nevery one knows the operation of nature on it,\nfor to a blind man it would be impossible to\nspeak of colours.\n\nThat we may not, however, appear too anxious\nto shun such an explanation, we would re-state\nwhat has been said as follows : colour is an\nelementary phenomenon in nature adapted to\nthe sense of vision ; a phenomenon which, like\nall others, exhibits itself by separation and con-\ntrast, by commixture and union, by augmenta-\ntion and neutralization, by communication and\ndissolution : under these general terms its\nnature may be best comprehended.\n\nWe do not press this mode of stating the sub-\nject on any one. Those who, like ourselves,\nfind it convenient, will readily adopt it ; but we\nhave no desire to enter the lists hereafter in\nits defence. From time immemorial it has been\ndangerous to treat of colour ; so much so, tliat\n\nINTRODUCTION. xH\n\none of our predecessors ventured on a certain\noccasion to say, ''The ox becomes furious\nif a red cloth is shown to hira ; but the philo-\nsopher, who speaks of colour only in a general\nway, begins to rave.\"\n\nNevertheless, if we are to proceed to give\nsome account of our work, to which we have\nappealed, we must begin by explaining how\nwe have classed the different conditions under\nwhich colour is produced. We found three\nmodes in which it appears; three classes of\ncolours, or rather three exhibitions of them\nall. The distinctions of these classes are easily\nexpressed.\n\nThus, in the first instance, we considered co-\nlours, as far as they may be said to belong to\nthe eye itself, and to depend on an action and\nre-action of the organ ; next, they attracted our\nattention as perceived in, or by means of, colour-\nless mediums ; and lastly, where we could con-\nsider them as belonging to particular substances.\nWe have denominated the first, physiological,\nthe second, physical, the third, chemical colours.\nThe first are fleeting and not to be arrested;\nthe next are passing, but still for a while en-\nduring; the last may be made permanent for\nany length of time.\n\nHaving separated these classes and kept them\nas distinct as possible, with a view to a clear,\ndidactic exposition, we have been enabled at\n\nXlii INTRODUCTION.\n\nthe same time to exhibit them io an unbroken\nseries, to connect the fleeting with the somewhat\nmore enduring, and these again with the per-\nmanent hues ; and thus, after having carefully\nattended to a distinct classification in the first\ninstance, to do away with it again when a larger\nview was desirable.\n\nIn a fourth division of our work we have\ntherefore treated generally what was previously\ndetailed under various particular conditions,\nand have thus, in fact, given a sketch for a\nfuture theory of colours. We will here only an-\nticipate our statements so far as to observe, that\nlight and darkness, brightness and obscurity, or\nif a more general expression is preferred, light\nand its absence, are necessary to the production\nof colour. Next to the light, a colour appears\nwhich we call yellow ; another appears next to\nthe darkness, which we name blue. When\ntliese, in their purest state, are so mixed that\nthey are exactly equal, they produce a third\ncolour called green. Each of the two first-named\ncolours can however of itself produce a new tint\nby being condensed or darkened. They thus\nacquire a reddish appearance which can be in-\ncreased to so great a degree that the original\nblue or yellow is hardly to be recognised in it :\nbut the intensest and purest red, especially in\nphysical cases, is produced when the two ex-\ntremes of the yellow-red and blue-red are\n\nINTRODUCTION. xl iii\n\nunited. This is the actual state of the appear-\nance and generation of colours. But we can\nalso assume an existing red in addition to the\ndefinite existing blue and yellow, and we can pro-\nduce contrariwise, by mixing, what we directly\nproduced by augmentation or deepening. With\nthese three or six colours, which may be con-\nveniently included in a circle, the elementary\ndoctrine of colours is alone concerned. All\nother modifications, which may be extended to\ninfinity, have reference more to the application, —\nhave reference to the technical operations of the\npainter and dyer, and the various purposes of\nartificial life. To point out another general\nquality, we may observe that colours throughout\nare to be considered as half-lights, as half-\nshadows, on which account if they are so mixed\nas reciprocally to destroy their specific hues, a\nshadowy tint, a grey, is produced.\n\nIn the fifth division of our inquiry we had\nproposed to point out the relations in which we\nshould wish our doctrine of colours to stand\nto other pursuits. Important as this part of our\nwork is, it is perhaps on this very account not\n80 successful as we could wish. Yet when we\nreflect that strictly speaking these relations\ncannot be described before they exist, we may\nconsole ourselves if we have in some degree\nfailed in endeavouring for the first time to\ndefine thera. For undoubtedly we should first\n\nXliv INTRODUCTION.\n\nwait to see how tliose whom we have endea-\nvoured to serve, to whom we have intended to\nmake an agreeable and useful offering, how such\npersons, we say, will accept the result of our\nutmost exertion : whether they will adopt it,\nwhether they will make use of it and follow it\nup, or whether they will repel, reject, and suffer\nit to remain unassisted and neglected.\n\nMeanwhile, we venture to express what we\nbelieve and hope. From the philosopher we\nbelieve we merit thanks for having traced the\nphenomena of colonics to their first sources, to\nthe circumstances under which they simply\nappear and are, and beyond which no further\nexplanation respecting them is possible. It will,\nbesides, be gratifying to him that we have ar-\nranged the appearances described in a form that\nadmits of being easily surveyed, even should he\nnot altogether approve of the arrangement itself.\n\nThe medical practitioner, especially him\nwhose study it is to watch over the organ of\nsight, to preserve it, to assist its defects and\nto cure its disorders, we reckon to make espe-\ncially our friend. In the chapter on the phy-\nsiological colours, in the Appendix relating to\nthose that are more strictly pathological, he will\nfind himself quite in his own province. We are\nnot without hopes of seeing the physiological\nphenomena, — a hitherto neglected, and, we may\nadd, most important branch of the theory of\n\nINTRODUCTION. xlv\n\ncolours,— completely investigated through the\nexertions of those individuals who in our own\ntimes are treating this department with success.\n\nThe investigator of nature should receive us\ncordially, since we enable him to exhibit the\ndoctrine of colours in the series of other ele-\nmentary phenomena, and at the same time\nenable him to make use of a corresponding no-\nmenclature, nay, almost the same words and\ndesignations as under the other rubrics. It is\ntrue we give him rather more trouble as a\nteacher, for the chapter of colours is not now to\nbe dismissed as heretofore with a few paragraphs\nand experiments ; nor will the scholar submit\nto be so scantily entertained as he has hitherto\nbeen, without murmuring. On the other hand,\nan advantage will afterwards arise out of this :\nfor if the Newtonian doctrine was easily learnt,\ninsurmountable difficulties presented themselvse\nin its application. Our theory is perhaps more\ndifficult to comprehend, but once known, all is\naccomplished, for it carries its application along\nwith it.\n\nThe chemist who looks upon colours as indi-\ncations by which he may detect the -more secret\nproperties of material things, has hitherto found\nmuch inconvenience in the denomination and\ndescription of colours ; nay, some have been in-\nduced after closer and nicer examination to look\nupon colour as an uncertain and falW\\o\\vs> cxv\n\nXlvi INTRODUCTION.\n\nterion in chemical operations. Yet we hope by\nmeans of our arrangement and the nomenclature\nbefore alluded to, to bring colour again into\ncredit, and to awaken the conviction that a pro-\ngressive, augmenting, mutable quality, a quality\nwhich admits of alteration even to inversion, is\nnot fallacious, but rather calculated to bring to\nlight the most delicate operations of nature.\n\nIn looking a little further round us, we are not\nwithout fears that we may fail to satisfy another\nclass of scientific men . By an extraordinary com-\nbination of circumstances the theory of colours\nhas been drawn into the province and before\nthe tribunal of the mathematician, a tribunal to\nwhich it cannot be said to be amenable. This\nwas owing to its affinity with the other laws of\nvision which the mathematician was legitimately\ncalled] upon to treat. It was owing, again, to\nanother circumstance: a great mathematician\nhad investigated the theory of colours, and\nhaving been mistaken in his observations as an\nexperimentalist, he employed the whole force of\nhis talent to give consistency to this mistake.\nWere both these circumstances considered, all\nmisunderstanding would presently be removed,\nand the mathematician would willingly co-\noperate with us, especially in the physical de-\npartment of the theory.\n\nTo the practical man, to the dyer, on the\nother hand, our labour must be altogether ac-\n\nINTRODUCTION. xlvil\n\nceptable; for it was precisely those who re-\nflected on the facts resulting from the opera-\ntions of dyeing who were the least satisfied with\nthe old theory : they were the first who per-\nceived the insufficiency of the Newtonian doc-\ntrine. The conclusions of men are very difierent\naccording to the mode in which they approach\na science or branch of knowledge ; from which\nside, through which door they enter. The\nliterally practical man, the manufacturer, whose\nattention is constantly and forcibly called to the\nfacts which occur under his eye, who experiences\nbenefit or detriment from the application of his\nconvictions, to whom loss of time and money is\nnot indifferent, who is desirous of advancing,\nwho aims at equalling or surpassing what others\nhave accomplished,— such a person feels the\nunsoundness and erroneousness of a theory\nmuch sooner than the man of letters, in whose\neyes words consecrated by authority are at last\nequivalent to solid coin; than the mathematician,\nwhose formula always remains infallible, even\nalthough the foundation on which it is con-\nstructed may not square with it. Again, to\ncarry on the figure before employed, in entering\nthis theory from the side of painting, from the\nside of aesthetic* colouring generally, we shall be\n\n• iEsthetic — belonging to taste as mere internal sense, from\naltrddyofiaty to feel ; the word was first used by WoU. — T .\n\nXlviii INTRODUCTION.\n\nfound to have accomplished a most thankworthy\noffice for the artist. In the sixth part we have\nendeavoured to define the effects of colour as ad-\ndressed at once to the eye and mind, with a view\nto making them more available for the purposes\nof art. Although much in this portion, and in-\ndeed throughout, has been suffered to remain as\na sketch, it should be remembered that all\ntheory can in strictness only point out leading\nprinciples, under the guidance of which, prac-\ntice may proceed with vigour and be enabled to\nattain legitimate results.\n\nPART I.\n\nPHYSIOLOGICAL COLOURS.\n\nWe naturally place these colours first, because\nthey belong altogether, or in a great degree, to\nthe mbject* — to the eye itself. They are the\nfoundation of the whole doctrine, and open to\nour view the chromatic harmony on which so\nmuch difference of opinion has existed. They\nhave been hitherto looked upon as extrinsic and\ncasual, as illusion and infirmity : their appear-\nances have been known from ancient date ; but,\nas they were too evanescent to be arrested, they\nwere banished into the region of phantoms, and\nunder this idea have been very variously described.\n\nThus they are called colores adventicii by Boyle ;\nimaginarii and phantcistici by Rizetti ; by Buffon,\ncouleurs accidentelles ; by Scherfer, scheinfarben\n(apparent colours) ; ocular illusions and deceptions\n\n* The Gennan distiDction between subject and object is so\ngenerally understood and adopted, that it is hardly necessary\nto explain that the subject is the individual, in this case the\nbeholder ; the object, all that in without him, — I.\n\n2 PHYSIOLOGICAL COLOURS.\n\nof sight by many ; by Hamberger, vitia Jugitiva ;\nby Darwin, ocular spectra.\n\nWe have called them physiological because\nthey belong to the eye in a healthy state ; be-\ncause we consider them as the necessary con-\nditions of vision ; the lively alternating action of\nwhich, with reference to external objects and a\nprinciple within it, is thus plainly indicated.\n\nTo these we subjoin the pathological colours,\nwhich, like all deviations from a constant law,\nafford a more complete insight into the nature of\nthe physiological colours.\n\nEFFECTS OF LIGHT AND DARKNESS ON THE EYE.\n\nThe retina, after being acted upon by light or\ndarkness, is found to be in two different states,\nwhich are entirely opposed to each other.\n\nIf we keep the eyes open in a totally dark\nplace, a certain sense of privation is experienced.\nThe organ is abandoned to itself; it retires into\nitself. That stimulating and grateful contact is\nwanting by means of which it is connected with\nthe external world, and becomes part of a whole.\n\nEFFECTS OF LIGHT AND DARKNESS. 3\n\nIf we look on a white, strongly illumined sur-\nface, the eye is dazzled, and for a time is in-\ncapable of distinguishing objects moderately\nlighted.\n\nThe whole of the retina is acted on in each of\nthese extreme states, and thus we can only ex-\nperience one of these effects at a time. In the\none case (6) we found the organ in the utmost\nrelaxation and susceptibility; in the other (7)\nin an overstrained state, and scarcely susceptible\nat all.\n\nIf we pass suddenly from the one state to the\nother, even without supposing these to be the\nextremes, but only, perhaps, a change from\nbright to dusky, the difference is remarkable,\nand we find that the effects last for some time.\n\nIn passing from bright daylight to a dusky\nplace we distinguish nothing at first : by degrees\nthe eye recovers its susceptibility ; strong eyes\nsooner than weak ones ; the former in a minute,\nwhile the latter may require seven or eight\nminutes.\n\nThe fact that the eye is not susceptible \\ofe\\wV\n\n4 EFFECTS OF LIGHT AND DARKNESS\n\nimpressions of light, if we pass from light to\ncomparative darkness, has led to curious mis-\ntakes in scientijfic observations. Thus an ob-\nserver; whose eyes required some time to recover\ntheir tone, was long under the impression that\nrotten wood did not emit light at noon-day, even\nin a dark room. The fact was, he did not see the\nfaint light, because he was in the habit of pass-\ning from bright sunshine to the dark room, and\nonly subsequently remained so long there that\nthe eye had time to recover itself\n\nThe same may have happened to Doctor\nWall, who, in the daytime, even in a dark room,\ncould hardly perceive the electric light of amber.\n\nOur not seeing the stars by day, as well as the\nimproved appearance of pictures seen through a\ndouble tube, is also to be attributed to the same\ncause.\n\nIf we pass from a totally dark place to one\nillumined by the sun, we are dazzled. In coming\nfrom a lesser degree of darkness to light that is\nnot dazzling, we perceive all objects clearer and\nbetter : hence eyes that have been in a state of\nrepose are in all cases better able to perceive\nmoderately distinct appearances.\n\nPrisoners who have been long confined in\ndarkness acquire so great a susceptibility of the\nretina, that even in the dark (probably a dark-\n\nON THE EYE. 5\n\nness very slightly illumined) they can still dis-\ntinguish objects.\n\nIn the act which we call seeing, the retina is\nat one and the same time in different and even\nopposite states. The greatest brightness, short\nof dazzling, acts near the greatest darkness. In\nthis state we at once perceive all the intermediate\ngradations of chiaro-scuroy and all the varieties of\nhues.\n\nWe will proceed in due order to consider and\nexamine these elements of the visible world, as\nwell as the relation in which the organ itself\nstands to them, and for this purpose we take the\nsimplest objects.\n\nII.\n\nEFFECTS OF BLACK AND WHITE OBJECTS ON THE EYE.\n\nIn the same manner as the retina generally is\naffected by brightness and darkness, so it is.\naffected by single bright or dark objects. If\nlight and dark produce different results on the\nwhole retina, so black and white objecl^ ^eew ^\\.\n\n6 EFFECTS OF BLACK AND\n\nthe same time produce the same states together\nwhich light and dark occasioned in succession.\n\nA dark object appears smaller than a bright\none of the same size. Let a white disk be placed\non a black ground, and a black disk on a white\nground, both being exactly similar in size ; let\nthem be seen together at some distance, and we\nshall pronounce the last to be about a fifth part\nsmaller than the other. If the black circle be\nmade larger by so much, they will appear equal.*\n\nThus Tycho de Brahe remarked that the moon\nin conjunction (the darker state) appears about\na fifth part smaller than when in opposition (the\nbright full state). The first crescent appears to\nbelong to a larger disk than the remaining dark\nportion, which can sometimes be distinguished\nat the period of the new moon. Black dresses\nmake people appear smaller than light ones.\nLights seen behind an edge make an apparent\nnotch in it. A ruler, behind which the flame of\na light just appears, seems to us indented. The\nrising or setting sun appears to make a notch in\nthe horizon.\n\nBlack, as the equivalent of darkness, leaves\n\nPlate i. fig. 1.\n\nWHITE OBJECTS ON THE EYE. 7\n\nthe organ in a state of repose ; white, as the re-\npresentative of light, excites it. We may, per-\nhaps» conclude from the above experiment (16)\nthat the unexcited retina, if left to itself, is drawn\ntogether, and occupies a less space than in its\nactive state, producedby the excitement of light.\nHence Kepler says very beautifully : ** Certum\nest vel in retind causs4 picturse, vel in spiritibus\ncauss^ impressionis, exsistere dilatationem luci-\ndorum.\" — Paralip. in Vitellionemy p. 220. Scher-\nfer expresses a similar conjecture. — Note A.\n\nHowever this may be, both impressions\nderived from such objects remain in the organ\nitself, and last for some time, even when the\nexternal cause is removed. In ordinary ex-\nperience we scarcely notice this, for objects\nare seldom presented to us which are very\nstrongly relieved from each other, and we avoid\nlooking at those appearances that dazzle the\nsight. In glancing from one object to another;\nthe succession of images appears to us distinct ;\nwe are not aware that some portion of the im-\npression derived from the object first contem-\nplated passes to that which is next looked at.\n\nIf in the morning, on waking, when the eye\nis very susceptible, we look intently at the bars\n\n8 EFFECTS OF BLACK AND\n\nof a window relieved against the dawning sky,\nand then shut our eyes or look towards a totally\ndark place, we shall see a dark cross on a light\nground before us for some time.\n\nEvery image occupies a certain space on the\nretina, and of course a greater or less space in\nproportion as the object is seen near or at a\ndistance. If we shut the eyes immediately\nafter looking at the sun we shall be surprised to\nfind how small the image it leaves appears.\n\nIf, on the other hand, we turn the open eye\ntowards the side of a room, and consider the\nvisionary image in relation to other objects, we\nshall always see it larger in proportion to the\ndistance of the surface on which it is thrown.\nThis is easily explained by the laws of perspec-\ntive, according to which a small object near\ncovers a great one at a distance.\n\nThe duration of these visionary impressions\nvaries with the powers or structure of the eye\nin different individuals, just as the time neces-\nsary for the recovery of the tone of the retina\nvaries in passing from brightness to darkness\n(10) : it can be measured by minutes and se-\n\nWHITE OBJECTS ON THE EYE. 9\n\nconds, indeed much more exactly than it could\nformerly have been by causing a lighted lin-\nstock to revolve rapidly, so as to appear a cir-\ncle. — Note B.\n\nBut the force with which an impinging light\nimpresses the eye is especially worthy of atten-\ntion. The image of the sun lasts longest ; other\nobjects, of various degrees of brightness, leave\nthe traces of their appearance on the eye for a\nproportionate time.\n\nThese images disappear by degrees, and\ndiminish at once in distinctness and in size.\n\nThey are reduced from the contour inwards,\nand the impression on some persons has been\nthat in square images the angles become gra-\ndually blunted till at last a diminished round\nimage floats before the eye.\n\nSuch an image, when its impression is no\nmore observable, can, immediately after, be\nagain revived on the retina by opening and\nshutting the eye, thus alternately exciting and\nresting it.\n\n10 EFFECTS OF BLACK AND\n\nImages may remain on the retina in morbid\naffections of the eye for fourteen, seventeen\nminutes, or even longer. This indicates extreme\nweakness of the organ, its inability to recover\nitself; while visions of persons or things which\nare the objects of love or aversion indicate the\nconnexion between sense and thought.\n\nIf, while the image of the window-bars before\nmentioned lasts, we look upon a light grey sur-\nface, the cross will then appear light and the\npanes dark. In the first case (20) the image\nwas like the original picture, so that the vision-\nary impression also could continue unchanged ;\nbut in the present instance our attention is\nexcited by a contrary effect being produced.\nVarious examples have been given by observers\nof nature.\n\nThe scientific men who made observations in\nthe Cordilleras saw a bright appearance round\nthe shadows of their heads on some clouds.\nThis example is a case in point ; for, while they\nfixed their eyes on the dark shadow, and at the\nsame time moved from the spot, the compensa-\ntory light image appeared to float round the\n\nWHITE OBJECTS ON THE EYE. 1 1\n\nreal dark one. If we look at a black disk on a\nlight grey surface, we shall presently, by\nchanging the direction of the eyes in the slight-\nest degree, see a bright halo floating round the\ndark circle.\n\nA similar circumstance happened to myself:\nfor while, as I sat in the open air, I was talking\nto a man who stood at a little distance from me\nrelieved on a grey sky, it appeared to me, as I\nslightly altered the direction of my eyes, after\nhaving for some time looked fixedly at him,\nthat his head was encircled with a dazzling\nlight.\n\nIn the same way probably might be explained\nthe circumstance that persons crossing dewy\nmeadows at sunrise see a brightness round each\nother's heads ;* the brightness in this case may\nbe also iridescent, as the phenomena of refrac-\ntion come into the account.\n\nThus again it has been asserted that the\nshadows of a balloon thrown on clouds were\nbordered with bright and somewhat variegated\ncircles.\n\nBeccaria made use of a paper kite in some\nexperiments on electricity. Round this kite\nappeared a small shining cloud varying in size ;\nthe same brightness was even observed round\npart of the string. Sometimes it disappeared,\n\n* See the Life of Benvenuto Cellini, vol. i. p. 453. ' Milan edi-\ntion, 1806.— T.\n\n12 EFFECTS OF BLACK AND*\n\nand if the kite moved faster the light appeared\nto float to and fro for a few moments on the\nplace before occupied. This appearance, which\ncould not be explained by those who observed\nit at the time, waa the image which the eye re-\ntained of the kite relieved as a dark mass on\na bright sky ; that image being changed into a\nlight mass on a comparatively dark back-\nground.\n\nIn optical and especially in chromatic expe-\nriments, where the observer has to do with\nbright lights whether colourless or coloured,\ngreat care should be taken that the spectrum\nwhich the eye retains in consequence of a pre-\nvious observation does not mix with the suc-\nceeding one, and thus afiect the distinctness\nand purity of the impression.\n\nThese appearances have been explained as\nfollows: That portion of the retina on which\nthe dark cross (29) was impressed is to be con-\nsidered in a state of repose and susceptibility.\nOn this portion therefore the moderately light\nsurface acted in a more lively manner than on\nthe rest of the retina, which had just been im-\npressed with the light through the panes, and\nwhich, having thus been excited by a much\nstronger brightness, could only view the grey\nsurface as a dark.\n\nWHITE OBJECTS ON THE EYE. 13\n\nThis mode of explanation appears sufficient\nfor the cases in question, but» in the considera-\ntion of phenomena hereafter to be adduced, we\nare forced to trace the eflfects to higher sources.\n\nThe eye after sleep exhibits its vital elas-\nticity more especially by its tendency to al-\nternate its impressions, which in the simplest\nform change from dark to light, and from light\nto dark. The eye cannot for a moment remain\nin a particular state determined by the object it\nlooks upon. On the contrary, it is forced to a\nsort of opposition, which, in contrasting extreme\nwith extreme, intermediate degree with inter-\nmediate degree, at the same time combines these\nopposite impressions, and thus ever tends to a\nwhole, whether the impressions are successive,\nor simultaneous and confined to one image.\n\nPerhaps the peculiarly grateful sensation\nM'hich we experience in looking at the skilfully\ntreated chiaro-scuro of colourless pictures and\nsimilar works of art arises chiefly from the\nsimultaneous impression of a whole, which by the\norgan itself is sought, rather than arrived at, in\nsuccession^ and which, whatever may be the re-\nsult, can never be arrested.\n\n■' \" • ■ '\n\n14 GREY SURFACES AND OBJECTS.\n\nIII.\n\nGREY SURFACES AND OBJECTS.\n\nA MODERATE light is cssential to many chro-\nmatic experiments. This can be presently ob-\ntained by surfaces more or less grey, and thus\nwe have at once to make ourselves acquainted\nwith this simplest kind of middle tint, with re-\ngard to which it is hardly necessary to observe,\nthat in many cases a white surface in shadow,\nor in a low light, may be considered equivalent\nto a grey.\n\nSince a grey surface is intermediate between\nbrightness and darkness, it admits of our illus-\ntrating a phenomenon before described (29) by\nan easy experiment.\n\nLet a black pbject be held before a grey sur-\nface, and let the spectator, after looking stead-\nfastly at it, keep his eyes unmoved while it is\ntaken away : the space it occupied appears\nmuch lighter. Let a white object be held up in\nthe same manner : on taking it away the space\nit occupied will appear much darker than the\n\nGREY SURFACES AND OBJECTS. 15\n\nrest of the surface. Let the spectator in both\ncases turn his eyes this way and that on the sur-\nface, the visionary images will move in like\nmanner.\n\nA grey object on a black ground appears\nmuch brighter than the same object on a white\nground. If both comparisons are seen together\nthe spectator can hardly persuade himself that\nthe two greys are identical. We believe this\nagain to be a proof of the great excitability of\nthe retina, and of the silent resistance which\nevery vital principle is forced to exhibit when\nany definite or immutable state is presented to\nit. Thus inspiration already presupposes ex-\npiration ; thus every systole its diastole. It is\nthe universal formula of life which manifests\nitself in this as in all other cases. When dark-\nness is presented to the eye it demands bright-\nness, and vice versd : it shows its vital energy,\nits fitness to receive the impression of the object,\nprecisely by spontaneously tending to an op-\nposite state.\n\n16 DAZZLING COLOURLESS OBJECTS.\n\nIV.\n\nDAZZLING COLOURLESS OBJECTS.\n\nIf we look at a dazzling, altogether colourless\nobject, it makes a strong lasting impression, and\nits after- vision is accompanied by an appearance\nof colour.\n\nLet a room be made as dark as possible ; let\nthere be a circular opening in the window-\nshutter about three inches in diameter, which\nmay be closed or not at pleasure. The sun\nbeing suffered to shine through this on a white\nsurface, let the spectator from some little dis-\ntance fix his eyes on the bright circle thus\nadmitted. The hole being then closed, let him\nlook towards the darkest part of the room ; a\ncircular image will now be seen to float before\nhim. The middle of this circle will appear\nbright, colourless, or somewhat yellow, but the\nborder will at the same moment appear red.\n\nAfter a time this red, increasing towards the\ncentre, covers the whole circle, and at last the\nbright central point. No sooner, however, is\nthe whole circle red than the edge begins to be\nblue, and the blue gradually encroaches inwards\n\nDAZZLING COLOURLESS OBJECTS. 17\n\non the red. When the whole is blue the edge\nbecomes dark and colourless. This darker edge\nagain slowly encroaches on the blue till the\nwhole circle appears colourless. The image\nthen becomes gradually fainter, and at the same\ntime diminishes in size. Here again we see\nhow the retina recovers itself by a succession of\nyibrations after the powerful external impression\nit received. (25,26.)\n\nBy several repetitions similar in result, I found\nthe comparative duration of these appearances\nin my own case to be as follows : —\n\nI looked on the bright circle five seconds, and\nthen, having closed the aperture, saw the co-\nloured visionary circle floating before me. After\nthirteen seconds it was altogether red ; twenty-\nnine seconds next elapsed till the whole was blue,\nand forty-eight seconds till it appeared colour-\nless. By shutting and opening the eye I con-\nstantly revived the image, so that it did not\nquite disappear till seven minutes had elapsed.\n\nFuture observers may find these periods\nshorter or longer as their eyes may be stronger\nor weaker C23), but it would be very remarkable\nif, notwithstanding such variations, a correspond-\ning proportion as to relative duration should be\nfound to exist.\n\ne\n\n18 DAZZLING COLOURLESS OBJECTS.\n\nBut this remarkable phenomenon no sooner\nexcites our attention than we observe a new\nmodification of it.\n\nIf we receive the impression of the bright\ncircle as before, and then look on a light grey\nsurface in a moderately lighted room, an image\nagain floats before us; but in this instance a\ndark one : by degrees it is encircled by a green\nborder that gradually spreads inwards over the\nwhole circle, as the red did in the former\ninstance. As soon as this has taken place a\ndingy yellow appears, and^ filling the space as\nthe blue did before, is finally lost in a negative\nshade.\n\nThese two experiments may be combined by\nplacing a black and a white plane surface next\neach other in a moderately lighted room, and\nthen looking alternately on one and the other\nas long as the impression of the light circle lasts :\nthe spectator will then perceive at first a red\nand green image alternately, and afterwards the\nother changes. After a little practice the two\nopposite colours may be perceived at once, by\ncausing the floating image to fall on the junction\nof the two planes. This can be more conve-\nniently done if the planes are at some distance,\nfor the spectrum then appears larger.\n\nDAZZLING COLOUBLE8S OBJECTS. 19\n\nI happened to be in a forge towards evening\nat the moment when a glowing mass of iron was\nplaced on the anvil ; I had fixed my eyes stead-\nfastly on it, and, turning round, I looked acci-\ndentally into an open coal- shed: a large red\nimage now floated before my eyes, and, as I\nturned them from the dark opening to the light\nboards of which the shed was constructed, the\nimage appeared half green, half red, according\nas it had a lighter or darker ground behind it.\nI did not at that time take notice of the sub-\nsequent changes of this appearance.\n\nThe' after- vision occasioned by a total dazzling\nof the retina corresponds with that of a circum-\nscribed bright object. The red colour seen by\npersons who are dazzled with snow belongs to\nthis class of phenomena, as well as the singularly\nbeautiful green colour which dark objects seem\nto wear after looking long on white paper in the\nsun. The details of such experiments may be\ninvestigated hereafter by those whose young\neyes are capable of enduring such trials further\nfor the sake of science.\n\nWith these examples we may also class the\nblack letters which in the evening light appear\n\n20 COLOURED OBJECTS.\n\n•\n\nred. Perhaps we might insert under the same\ncategory the story that drops of blood appeared\non the table at which Henry IV. of France had\nseated himself with the Due de Guise to play at\ndice.\n\nV.\n\nCOLOURED OBJECTS.\n\nWe have hitherto seen the physiological\ncolours displayed in the after-vision of colour-\nless bright objects, and also in the after-vision\nof general colourless brightness ; we shall now\nfind analogous appearances if a given colour be\npresented to the eye: in considering this, all\nthat has been hitherto detailed must be present\nto our recollection.\n\nThe impression of coloured objects remains\nin the eye like that of colourless ones, but in\nthis case the energy of the retina, stimulated as\nit is to produce the opposite colour, will be more\napparent.\n\nLet a small piece of bright- coloured paper or\nsilk stuflf be held before a moderately lighted\nwhite surface ; lef the observer look steadfastly\n\nCOLOURED OBJECTS. 2 I\n\non the small coloured object, and let it be taken\naway after a time while his eyes remain un-\nmoved ; the spectrum of another colour will then\nbe visible on the white plane. The coloured\npaper may be also left in its place while the eye\nis directed to another part of the white plane ;\nthe same spectrum will be visible there too, for\nit arises from an image which now belongs to\nthe eye.\n\nIn order at once to see what colour will be\nevoked by this contrast, the chromatic circle *\nmay be referred to. The colours are here ar-\nranged in a general way according to the\nnatural order, and the arrangement will be\nfound to be directly applicable in the present\ncase ; for the colours diametrically opposed to\neach other in this diagram are those which reci*\nprocally evoke each other in the eye. Thus,\nyellow demands purple ; orange, blue ; red,\ngreen; and vice versd: thus again all interme-\ndiate gradations reciprocally evoke each other ;\nthe simpler colour demanding the compound,\nand vice versd. — Note C.\n\nThe cases here under consideration occur\noftener than we are aware in ordinary life ; in-\n\n♦PJate 1,% 3.\n\n22 COLOURED OBJECTS.\n\ndeed, an attentive observer sees these appear-\nances everywhere, while, on the other hand, the\nuninstructed, like our predecessors, consider\nthem as temporary visual defects, sometimes\neven as symptoms of disorders in the eye, thus\nexciting serious apprehensions. A few remark-\nable instances may here be inserted.\n\nI had entered an inn towards evening, and,\nas a well-favoured girl, with a brilliantly fair\ncomplexion, black hair, and a scarlet bodice,\ncame into the room, I looked attentively at her\nas she stood before me at some distance in half\nshadow. As she presently afterwards turned\naway, I saw on the white wall, which was now\nbefore me, a black face surrounded with a bright\nlight, while the dress of the perfectly distinct\nfigure appeared of a beautiful sea-green.\n\nAmong the materials for optical experiments,\nthere are portraits with colours and shadows\nexactly opposite to the appearance of nature.\nThe spectator, after having looked at one of\nthese for a time, will see the visionary figure\ntolerably true to nature. This is conformable\nto the same principles, and consistent with ex-\nperience, for, in the former instance, a negress\nwith a white head-dress would have given me a\nwhhe face surrounded with black. In the case\n\nCOLOURED OBJECTS. 23\n\nof the painted figures, however, which are com-\nmonly smally the parts are not distinguishable\nby every one in the after-image.\n\nA phenomenon which has before excited\nattention among the observers of nature is to\nbe attributed, I am persuaded, to the same\ncause.\n\nIt has been stated that certain flowers, towards\nevening in summer, coruscate, become phos-\nphorescent, or emit a momentary light. Some\npersons have described their observation of\"\nthis minutely. I had often endeavoured to\nwitness it myself, and had even resorted to\nartificial contrivances to produce it.\n\nOn the 19th of June, 1799, late in the evening,\nwhen the twilight was deepening into a clear\nnight, as I was walking up and down the garden\nwith a friend, we very distinctly observed a\nflame-like appearance near the oriental poppy,\nthe flowers of which are remarkable for their\npowerful red colour. We approached the place\nand looked attentively at the flowers, but could\nperceive nothing further, till at last, by passing\nand repassing repeatedly, while we looked side-\nways on them, we succeeded in renewing the\nappearance as often as we pleased. It proved\nto be a physiological phenomenon, such as\nothers we bare described, and \\\\\\e ^^^^\\^\\\\V\n\n^^^\n\n24 COLOURED OBJECTS.\n\ncoruscation was nothiug but the spectrum of the\nflower in the compensatory blue-green colour.\n\nIn looking directly at a flower the image is\nnot produced, but it appears immediately as the\ndirection of the eye is altered. Again, by look-\ning sideways on the object, a double image is\nseen for a moment, for the spectrum then\nappears near and on the real object.\n\nThe twilight accounts for the eye being in a\nperfect state of repose, and thus very susceptible,\naqd the colour of the poppy is sufficiently\npowerful in the summer twilight of the longest\ndays to act with full efiect and produce a com-\npensatory image. I have no doubt these ap-\npearances might be reduced to experiment, and\nthe same effect produced by pieces of coloured\npaper. Those who wish to take the most\neffectual means for observing the appearance in\nnature — suppose in a garden — should fix the eyes\non the bright flowers selected for the purpose,\nand, immediately after, look on the gravel path.\nThis will be seen studded with spots of the\nopposite colour. The experiment is practicable\non a cloudy day, and even in the brightest sun-\nshine, for the sun-light, by enhancing the bril-\nliancy of the flower, renders it fit to produce the\ncompensatory colour sufficiently distinct to be\nperceptible even in a bright light. Thus, peonies\nproduce beautiful green, marigolds vivid blue\nspectra.\n\nCOLOURED OBJECTS. 25\n\nAs the opposite colour is produced by a con-\nstant law in experiments with coloured objects\non portions of the retina, so the same effect\ntakes place when the whole retina is impressed\nwith a single colour. We may convince our-\nselves of this by means of coloured glasses. If\nwe look long through a blue pane of glass,\neverything will afterwards appear in sunshine to\nthe naked eye, even if the sky is grey and the\nscene colourless. In like manner, in taking off\ngreen spectacles, we see all objects in a red\nlight. Every decided colour does a certain vio-\nlence to the eye, and forces the organ to\nopposition.\n\nWe have hitherto seen the opposite colours\nproducing each other successively on the retina :\nit now remains to show by experiment that the\nsame effects can exist simultaneously. If a\ncoloured object impinges on one part of the\nretina, the remaining portion at the same mo-\nment has a tendency to produce the compensa-\ntory colour. To pursue a former experiment, if\nwe look on a yellow piece of paper placed on a\nwhite surface, the remaining part of the organ\nhas already a tendency to produce a purple hue\non the colourless surface : in this case the small\nportion of yellow is not powerfuV ev\\o\\x^\\\\ \\.o \\it<^-\n\n26 COLOURED OBJECTS.\n\nduce this appearance distinctly, but, if a white\npaper is placed on a yellow wall, we shall see\nthe white tinged with a purple hue.\n\nAlthough this experiment may be made with\nany colours, yet red and green are particularly\nrecommended for it, because these colours seem\npowerfully to evoke each other. Numerous in-\nstances occur in daily experience. If a green\npaper is seen through striped or flowered muslin,\nthe stripes or flowers will appear reddish. A\ngrey building seen through green pallisades\nappears in like manner reddish. A modification\nof this tint in the agitated sea is also a com-\npensatory colour : the light side of the waves\nappears green in its own colour, and the sha-\ndowed side is tinged with the opposite hue. The\ndifferent direction of the waves with reference\nto the eye produces the same effect. Objects\nseen through an opening in a red or green cur-\ntain appear to wear the opposite hue. These\nappearances will present themselves to the atten-\ntive observer on all occasions, even to an un-\npleasant degree.\n\nHaving made ourselves acquainted with the\nsimultaneous exhibition of these eflects in direct\ncases, we shall find that we can also observe\niheoj by indirect means. If we place a piece of\n\nCOLOURED OBJECTS. 27\n\npaper of a bright orange colour on the white\nsurface, we shall, after looking intently at it,\nscarcely perceive the compensatory colour on\nthe rest of the surface : but when we take the\norange paper away, and when the blue spectrum\nappears in its place, immediately as this spec-\ntrum becomes fully apparent, the rest of the\nsurface will be overspread, as if by a flash, with\na reddish-yellow light, thus exhibiting to the\nspectator in a lively manner the productive\nenergy of the organ, in constant conformity with\nthe same law.\n\nAs the compensatory colours easily appear,\nwhere they do not exist in nature, near and\nafter the original opposite ones, so they are ren-\ndered more intense where they happen to mix\nwith a similar real hue. In a court which was\npaved with grey limestone flags, between which\ngrass had grown, the grass appeared of an ex-\ntremely beautiful green when the evening clouds\nthrew a scarcely perceptible reddish light on\nthe pavement. In an opposite case we find,\nin walking through meadows, where we see\nscarcely anything but green, the stems of trees\nand the roads often gleam with a reddish hue.\nThis tone is not uncommon in the works of\nlandscape painters, especially those who prac-\ntice in water-coJoiirs : they pToW\\A^ ^^^ \\\\.\\w\n\n00mi^limmmi\\ itm^ t i\n\n28 COLOURED OBJECTS.\n\nnature, and thus, unconsciously imitating it,\ntheir colouring is criticised as unnatural.\n\nThese phenomena are of the greatest import-\nance, since they direct our attention to the laws\nof vision, and are a necessary preparation for\nfuture observations on colours. They show that\nthe eye especially demands completeness, and\nseeks to eke out the colorific circle in itself.\nThe purple or violet colour suggested by yellow\ncontains red and blue ; orange, which responds\nto blue, is composed of yellow and red ; green,\nuniting blue and yellow, demands red ; and so\nthrough all gradations of the most complicated\ncombinations. That we are compelled in this\ncase to assume three leading colours has been\nalready remarked by other observers.\n\nWhen in this completeness the elements of\nwhich it is composed are still appreciable by\nthe eye, the result is justly called harmony.\nWe shall subsequently endeavour to show how\nthe theory of the harmony of colours may be\ndeduced from these phenomena, and how, sim-\nply through these qualities, colours may be ca-\npable of being applied to aesthetic purposes.\nThis will be shown when we have gone through\nthe whole circle of our observations, returning\nto the point from which we started.\n\nCOLOURED SHADOWS. 29\n\nVI.\n\nCOLOURED SHADOWS.\n\nBefore, however, we proceed further, we have\nyet to observe some very remarkable cases of\nthe vivacity with which the suggested colours\nappear in the neighbourhood of others : we al-\nlude to coloured shadows. To arrive at these\nwe first turn our attention to shadows that are\ncolourless or negative.\n\nA shadow cast by the sun, in its full bright-\nness, on a white surface, gives us no impression\nof colour ; it appears black, or, if a contrary\nlight (here assumed to differ only in degree) can\nact upon it, it is only weaker, half-lighted, grey.\n\nTwo conditions are necessary for the existence\nof coloured shadows: first, that the principal\nlight tinge the white surface with some hue ;\nsecondly, that a contrary light illumine to a\ncertain extent the cast shadow.\n\nLet a short, lighted candle be placed at twi-\nlight on a sheet of white paper. Between it\nand the declining daylight let a pencil be placed\n\n•ppf\n\n30 COLOURED SHADOWS.\n\nupright, so that its shadow thrown by the candle\nmay be lighted, but not overcome, by the weak\ndaylight : the shadow will appear of the most\nbeautiful blue.\n\nThat this shadow is blue is immediately evi-\ndent; but we can only persuade ourselves by\nsome attention that the white paper acts as a\nreddish yellow, by means of which the comple-\nmental blue is excited in the eye. — Note D.\n\nIn all coloured shadows, therefore, we must\npresuppose a colour excited or suggested by the\nhue of the surface on which the shadow is\nthrown. This may be easily found to be the\ncase by attentive consideration, but we may\nconvince ourselves at once by the following ex-\nperiment.\n\nPlace two candles at night opposite each\nother on a white surface ; hold a thin rod be-\ntween them upright, so that two shadows be\ncast by it ; take a coloured glass and hold it be-\nfore one of the lights, so that the white paper\nappear coloured ; at the same moment the sha-\ndow cast by the coloured light and slightly illu-\nmined by the colourless one will exhibit the\ncomplemental hue.\n\nCOLOURED SHADOWS. 31\n\nAn important consideration suggests itself\nhere, to which we shall frequently have occasion\nto return. Colour itself is a degree of darkness\n(o-xiepov) ; hence Kircher is perfectly right in\ncalling it lumen opacatum. As it is allied to\nshadow, so it combines readily with it; it ap-\npears to us readily in and by means of shadow\nthe moment a suggesting cause presents itself.\nWe could not refrain from adverting at once to\na fact which we propose to trace and develop\nhereafter. — Note E.\n\nSelect the moment in twilight when the light\nof the sky is still powerful enough to cast a sha-\ndow which cannot be entirely effaced by the\nlight of a candle. The candle may be so placed\nthat a double shadow shall be visible, one from\nthe candle towards the daylight, and another\nfrom the daylight towards the candle. If the\nformer is blue the latter will appear orange-\nyellow : this orange-yellow is in fact, however,\nonly the yellow-red light of the candle diffused\nover the whole paper, and which becomes visible\nin shadow.\n\nThis is best exemplified by the former expe-\nriment with two candles and coloured glasses.\n\n32 COLOURED SHADOWS.\n\nThe surprising readiness with which shadow as-\nsumes a colour will again invite our attention\nin the further consideration of reflections and\nelsewhere. ,\n\nThus the phenomena of coloured shadows\nmay be traced to their cause without diflficulty.\nHenceforth let any one who sees an instance of\nthe kind observe only with what hue the light\nsurface on which they are thrown is tinged.\nNay, the colour of the shadow may be considered\nas a chromatoscope of the illumined surface, for\nthe spectator may always assume the colour of\nthe light to be the opposite of that of the sha-\ndow, and by an attentive examination may as-\ncertain this to be the fact in every instance.\n\nThese appearances have been a source of\ngreat perplexity to former observers: for, as\nthey were remarked chiefly in the open air,\nwhere they commonly appeared blue, they were\nattributed to a certain inherent blue or blue co-\nlouring quality in the air. The inquirer can,\nhowever, convince himself, by the experiment\nwith the candle in a room, that no kind of blue\nlight or reflection is necessary to produce the\neffect in question. The experiment may be\nmade on a cloudy day with white curtains drawn\n\nCOLOURED SHADOWS. 33\n\nbefore the light, and in a room where no trace\nof blue exists, and the blue shadow will be only\nso much the more beautiful.\n\nDe Saussure, in the description of his ascent\nof Mont Blanc, says, \" A second remark, which\nmay not be uninteresting, relates to the colour\nof the shadows. These, notwithstanding the\nmost attentive obseryation, we neyer found dark\nblue, although this had been frequently the case\nin the plain. On the contrary, in fifty-nine in-\nstances we saw them once yellowish, six times\npale bluish, eighteen times colourless or black,\nand thirty-four times pale violet. Some natural\nphilosophers suppose that these colours arise\nfrom accidental vapours diffused in the air, which\ncommunicate their own hues to the shadows ;\nnot that the colours of the shadows are occa-\nsioned by the reflection of any given sky colour\nor interposition of any given air colour : the\nabove observations seem to favour this opinion.\"\nThe instances given by De Saussure may be\nnow explained and classed with analogous ex-\namples without difficulty.\n\nAt a great elevation the sky was generally\nfree from vapours, the sun shone in full force on\nthe snow, so that it appeared perfectly white to\nthe eye : in this case they saw the shadows\nquite colourless. If the air was charged '^xVVn. ^\n\n34 COLOURED SHADOWS.\n\ncertain degree of vapour, in consequence of\nwhich the light snow would assume a yellowish\ntone, the shadows were yiolet-coloured, and this\neffect, it appears, occurred oftenest. They saw\nalso bluish shadows, but this happened less fre-\nquently ; qnd that the blue and violet were pale\nwas owing to the surrounding brightness, by\nwhich the strength of the shadows was miti-\ngated. Once only they saw the shadow yellow-\nish : in this case, as we have already seen (70),\nthe shadow is cast by a colourless light, and\nslightly illumined by a coloured one.\n\nIn travelling over the Harz in winter, I hap-\npened to descend from the Brocken towards\nevening ; the wide slopes extending above and\nbelow me, the heath, every insulated tree and\nprojecting rock, and all masses of both, were\ncovered with snow or hoar-frost. The sun was\nsinking towards the Oder ponds.* During the\nday, owing to the yellowish hue of the snow,\nshadows tending to violet had already been ob-\nservable ; these might now be pronounced to be\ndecidedly blue, as the illumined parts exhibited\na yellow deepening to orange.\n\nBut as the sun at last was about to set, and\nits rays, greatly mitigated by the thicker va-\n\n* Reservoirs in which water is collected from various small\nBtreama, to worli the mines. — T.\n\nCOLOURED SHADOWS. 35 ^\n\npours, began to diffuse a most beautiful red\ncolour over the whole scene around me, the\nshadow colour changed to a green, in lightness\nto be compared to a sea-green, in beauty to the\ngreen of the emerald. The appearance became\nmore and more vivid : one might have imagined\noneself in a fairy world, for every object had\nclothed itself in the two vivid and so beautifully\nharmonising colours, till at last, as the sun went\ndown, the magnificent spectacle was lost in a\ngrey twilight, and by degrees in a clear moon-\nand-starlight night.\n\nOne of the most beautiful instances of co-\nloured shadows may be observed during the\nfull moon. The candle-light and moon-light\nmay be contrived to be exactly equal in\nforce; both shadows may.be exhibited with\nequal strength and clearness, so that both co-\nlours balance each other perfectly. A white\nsurface being placed opposite the full moon,\nand the candle being placed a little on one side\nat a due distance, an opaque body is held be-\nfore the white plane A double shadow will\nthen be seen : that cast by the moon and illu*\nmined by the candle-light will be a powerful\nred-yellow ; and contrariwise, that cast by the\ncandle and illumined by the moon will appear\nof the most beautiful blue. The «»V\\ado^ , q.q\\sv-\nposed of the union of the two sVv^^ovjs, >«\\vfcx^\n\n36 COLOURED SHADOWS.\n\nthey cross each other, is black. The yellow\nshadow (74) cannot perhaps be exhibited in a\nmore striking manner. The immediate vicinity\nof the blue and the interposing black shadow\nmake the appearance the more agreeable. It\nwill even be found, if the eye dwells long on\nthese colours, that they mutually evoke and\nenhance each other, the increasing red in the\none still producing its contrast, viz. a kind of\nsea-green .\n\nWe are here led to remark that in this, and\nin all cases, a moment or two may perhaps be\nnecessary to produce the complemental colour-\nThe retina must be first thoroughly impressed\nwith the demanding hue before the responding\none can be distinctly observable.\n\nWhen divers are under water, and the sun-\nlight shines into the diving-bell, everything is\nseen in a red light (the cause of which will be\nexplained hereafter), while the shadows appear\ngreen. The very same phenomenon which I\nobserved on a high mountain (75) is presented\nto others in the depths of the sea, and thus Na-\nture throughout is in harmony with herself.\n\nSome observations and experiments which\nequally illustrate what has been stated with re-\n\nCOLOURED SHADOWS. 37\n\ngard to coloured objects and coloured shadows\nmay be here added. Let a white paper blind\nbe fastened inside the window on a winter even-\ning; in this blind let there be an opening,\nthrough which the snow of some neighbouring\nroof can be seen. Towards dusk let a candle be\nbrought into the room ; the snow seen through\nthe opening will then appear perfectly blue, be-\ncause the paper is tinged with warm yellow by\nthe candle-light. The snow seen through the\naperture is here equivalent to a shadow illu-\nmined by a contrary light (76), and may also\nrepresent a grey disk on a coloured surface (56).\n\nAnother very interesting experiment may\nconclude these examples. If we take a piece\nof green glass of some thickness, and hold it so\nthat the window bars be reflected in it, they\nwill appear double owing to the thickness of the\nglass. The image which is reflected from the\nunder surface of the glass will be green ; the\nimage which is reflected from the upper surface,\nand which should be colourless, will appear red.\n\nThe experiment may be very satisfactorily\nmade by pouring water into a vessel, the inner\nsurface of which can act as a mirror ; for both\nreflections may first be seen colourless while the\nwater is pure, and then by tinging it, they will\nexhibit two opposite hues.\n\n38 FAINT LIGHTS.\n\nVII.\n\nFAINT LIGHTS.\n\nLight, in its full force, appears purely white,\nand it gives this impression also in its highest\ndegree of dazzling splendour. Light, which is\nnot so powerful, can also, under various condi-\ntions, remain colourless. Several naturalists\nand mathematicians have endeavoured to mea-\nsure its degrees — Lambert, Bouguer, Rumfort.\n\nYet an appearance of colour presently mani-\nfests itself in fainter lights, for in their relation\nto absolute light they resemble the coloured\nspectra of dazzling objects (39).\n\n83.;\n\nA light of any kind becomes weaker, either\nwhen its own force, from Whatever cause, is di-\nminished, or when the eye is so circumstanced\nor placed, that it cannot be sufficiently im-\npressed by the action of the light. Those ap-\npearances which may be called objective, come\nunder the head of physical colours. We will\nonly advert here to the transition from white to\nred heat in glowing iron. We may also observe\n\nFAINT LIGHTS. 39\n\nthat the flames of lights at night appear redder\nin proportion to their distance from the eye. —\nNoteF.\n\nCandle-light at night acts as yellow when seen\nnear ; we can perceive this by the efiect it pro-\nduces on other colours. At night a pale yellow\nis hardly to be distinguished from white ; blue\napproaches to green, and rose-colour to orange.\n\nCandle-light at twilight acts powerfully as a\nyellow light : this is best proved by the purple\nblue shadows which, under these circumstances,\nare evoked by the eye.\n\nThe retina may be so excited by a strong\nlight that it cannot perceive fainter lights (II) :\nif it j>erceive these they appear coloured : hence\ncandle-light by day appears reddish, thus re-\nsembling, in its relation to fuller light, the spec-\ntrum of a dazzling object ; nay, if at night we\nlook long and intently on the flame of a light,\nit appears to increase in redness.\n\nThere are faint lights which, notwithstanding\ntheir moderate lustre, give an impression of a\n\n40 FAINT LIGHTS.\n\nwhite, or, at the most, of a light yellow appear-\nance on the retina ; such as the moon in its full\nsplendour. Rotten wood has even a kind of\nbluish light. All this will hereafter be the\nsubject of further remarks.\n\nIf at night we place a light near a white or\ngreyish wall so that the surface be illumined\nfrom this central point to some extent, we find,\non observing the spreading light at some dis-\ntance, that the boundary of the illumined surface\nappears to be surrounded with a yellow circle,\nwhich on the outside tends to red-yellow. We\nthus observe that when light direct or reflected\ndoes not act in its full force, it gives an impres*\nsion of yellow, of reddish, and lastly even of red.\nHere we find the transition td halos which we\nare accustomed to see in some mode or other\nround luminous points.\n\nVIII.\n\nSUBJECTIVE HALOS.\n\nHalos may be divided into subjective and ob-\njective. The latter will be considered under the\nphysical colours ; the first only belong here.\nThese are distinguished from the objective\n\n' SUBJECTIVE HALOS. 41\n\nhalos by the circumstance of their vanishiug\nwhen the point of light which produces them on\nthe retina is covered.\n\nWe have before noticed the impression of a\nluminous object on the retina, and seen that it\nappears larger : but the effect is not at an end\nhere, it is not confined to the impression of the\nimage; an expansive action also takes place,\nspreading from the centre.\n\nThat a nimbus of this kind is produced round\nthe luminous image in the eye may be best seen\nin a dark room, if we look towards a moderately\nlarge opening in the window-shutter. In this\ncase the bright image is surrounded by a cir-\ncular misty light. I saw such a halo bounded\nby a yellow and yellow-red circle on opening\nmy eyes at dawn, on an occasion when I passed\nseveral nights in a bed-carriage.\n\nHalos appear most vivid when the eye is sus-\nceptible from having been in a state of repose.\nA dark background also heightens their ap-\npearance. Both causes account for our seeing\nthem so strong if a light is presented to the eyes\n\n42 SUBJECTIVE UALOS.\n\non waking at night. These conditions were\ncombined when Descartes after sleeping, as he\nsat in a ship, remarked such a vividly-coloured\nhalo round the light.\n\nA light must shine moderately, not dazzle, in\norder to produce the impression of a halo in the\neye ; at all events the halos of dazzling lights\ncannot be observed. We see a splendour of\nthis kind round the image of the sun reflected\nfrom the surface of water.\n\nA halo of this description, attentively observed,\nis found to be encircled towards its edge with a\nyellow border: but even here the expansive\naction, before alluded to^ is not at an end, but\nappears still to extend in varied circles.\n\nSeveral cases seem to indicate a circular ac-\ntion of the retina, whether owing to the round\nform of the eye itself and its diflFerent parts, or\nto some other cause.\n\nIf the eye is pressed only in a slight degree\nfrom the inner corner, darker or lighter circles\n\nSUBJECTIVE HALOS. 43\n\nappear. At night, even without pressure, we\ncan sometimes perceive a succession of such\ncircles emerging from, or spreading over, each\nother.\n\nWe have already seen that a yellow border is\napparent round the white space illumined by a\nlight placed near it. This may be a kind of\nobjective halo. (88.)\n\nSubjective halos may be considered as the\nresult of a conflict between the light and a living\nsurface. From the conflict between the excit-\ning principle and the excited, an undulating\nmotion arises, which may be illustrated by a\ncomparison with the circles on water. The\nstone thrown in drives the water in all direc-\ntions ; the efiect attains a maximum, it reacts,\nand being opposed, continues under the surface.\nThe effect goes on, culminates again, and thus\nthe circles are repeated. If we have ever re-\nmarked the concentric rings which appear in a\nglass of water on trying to produce a tone by\nrubbing the edge ; if we call to mind the inter-\nmitting pulsations in the reverberations of bells,\nwe shall approach a conception of what may\ntake place on the retina when the image of a\nluminous object impinges on it, not to meuUovx\n\nSUBJECTIVE HALOS.\n\nthat as a living and elastic structure, it has al-\nready a circular principle in its organisation. —\nNote G.\n\nThe bright circular space vphich appears\nround the shining object is yellow, ending in\nred: then follows a greenish circle^ which is\nterminated by a red border. This appears to be\nthe usual phenomenon where the luminous body\nis somewhat considerable in size. These halos\nbecome greater the more distant we are from\nthe luminous object.\n\nHalos may, however, appear extremely small\nand numerous when the impinging image is\nminute, yet powerful,, in its effect. The ex*\nperiment is best made with a piece of gold-leaf\nplaced on the ground and illumined by the sun.\nIn these cases the halos appear in variegated\nrays. The iridescent appearance produced in\nthe eye when the sun pierces through the leaves\nof trees seems also to belong to the same class\nof phenomena.\n\n..., * ■— -\n\nPATHOLOGICAL COLOURS.\n\nAPPENDIX.\n\nWe are now sufficiently acquainted with the\nphysiological colours to distinguish them from\nthe pathological. We know what appearances\nbelong to the eye in a healthy state, and are ne-\ncessary to enable the organ to exert its complete\nvitality and activity.\n\nMorbid phenomena indicate in like manner\nthe existence of organic and physical laws : for\nif a living being deviates from those rules with\nreference to which it is constructed, it still seeks\nto agree with the general vitality of nature in\nconformity with general laws, and throughout its\nwhole course still proves the constancy of those\nprinciples on which the universe has existed,\nand by which it is held together.\n\nWe will here first advert to a very remarkable\nstate in which the vision of many persons is\nfound to be. As it presents a deviation from\nthe ordinary mode of seeing colours, it might\nbe fairly classed under morbid impressions ; but\nas it is consistent in itself, as it often occurs,\n\n46 PATHOLOGICAL COLOURS.\n\nmay extend to several members of a family, and\nprobably does not a^mit of cure, we may con-\nsider it as bordering only on the nosological\ncases, and therefore place it first.\n\nI was acquainted with two individuals not\nmore than twenty years of age, who were thus\naffected: both had bluish-grey eyes, an acute\nsight for near and distant objects, by day-light\nand candle-light, and their mode of seeing\ncolours was in the main quite similar.\n\nThey agreed with the rest of the world in\ndenominating white, black, and grey in the usual\nmanner. Both saw white untinged with any\nhue. One saw a somewhat brownish appear-\nance in black, and in grey a somewhat reddish\ntinge. In general they appeared to have a very\ndelicate perception of the gradations of light\nand dark.\n\nThey appeared to see yellow, red-yellow, and\nyellow-red,* like others : in the last case they said\nthey saw the yellow passing as it were over the\nred as if glazed : some thickly-ground carmine,\nwhich had dried in a saucer, they called red.\n\n* It has been found necessary to follow the author s nomencla^\nture throughout. — T.\n\nPATHOLOGICAL COLOURS. 47\n\nBut now a striking difference presented itself.\nIf the carmine was passed thinly over the white\nsaucer, they would compare the light colour thus\nproduced to the colour of the sky, and call it\nblue. If a rose was shown them beside it, they\nwould, in like manner, call it blue ; and in all the\ntrials which were made, it appeared that they\ncould not distinguish light blue from rose-colour.\nThey confounded rose-colour, blue, and violet on\nall occasions: these colours only appeared to\nthem to be distinguished from each other by de-\nlicate shades of lighter, darker, in tenser, or\nfainter appearance.\n\nAgain they could not distinguish green from\ndark orange, nor, more especially, from a red\nbrown.\n\nIf any one, accidentally conversing with these\nindividuals, happened to question them about\nsurrounding objects, their answers occasioned\nthe greatest perplexity, and the interrogator\nbegan to fancy his own wits were out of order.\nWith some method we may, however, approach\nto a nearer knowledge of the law of this devia-\ntion from the general law.\n\n48 PATHOLOGICAL COLOURS.\n\nThese persons, as may be gathered from what\nhas been stated, saw fewer colours than other\npeople : hence arose the confusion of different\ncolours. They called the sky rose-colour, and\nthe rose blue, or vice versa. The question now\nis : did they see both blue or both rose-colour ?\ndid they see green orange, or orange green ?\n\nThis singular enigma appears to solve itself,\nif we assume that they saw no blue, but, instead\nof it, a light pure red, a rose-colour. We can\ncomprehend what would be the result of this by\nmeans of the chromatic diagram.\n\nIf we take away blue from the chromatic\ncircle we shall miss violet and green as well.\nPure red occupies the place of blue and violet,\nand in again mixing with yellow the red pro-\nduces orange where green should be.\n\nProfessing to be satisfied with this mode of\nexplanation, we have named this remarkable de-\nviation from ordinary vision \" Acyanoblepsia.\" *\nWe have prepared some coloured figures for\n\n♦ Non-perception of blue.\n\nPATHOLOGICAL COLOURS. 49\n\nits further elucidation^ and in explaining these\nwe shall add some further details. Among the\nexamples will be found a landscape, coloured in\nthe mode in which the individuals alluded to\nappeared to see nature : the sky rose-colour, and\nall that should be green varying from yellow to\nbrown red, nearly as foliage appears to us in\nautumn * — Note H.\n\nWe now proceed to speak of morbid and other\nextraordinary affections of the retina, by which\nthe eye may be susceptible of an appearance of\nlight without external light, reserving for a\nfuture occasion the consideration of galvanic\nlight.\n\nIf the eye receives a blow, sparks seem to\nspread from it. In some states of body, again,\nwhen the blood is heated, and the system much\nexcited, if the eye is pressed first gently, and\nthen more and more strongly, a dazzling and\nintolerable light may be excited.\n\nIf those who have been recently couched ex-\nperience pain and heat in the eye, they fre-\n\n* It has not been thought necessary to copy the plates here\nreferred to. — T.\n\n50 PATHOLOGICAL COLOURS.\n\nquently see fiery flashes and sparks : these\nsymptoms last sometimes for a week or fortnight,\nor till the pain and heat diminish.\n\nA person suffering from ear-ache saw sparks\nand balls of light in the eye during each attack,\nas long as the pain lasted.\n\nPersons suffering from worms often experience\nextraordinary appearances in the eye, sometimes\nsparks of fire, sometimes spectres of light, some-\ntimes frightful figures, which they cannot by an\neffort of the will cease to see : sometimes these\nappearances are double.\n\nHypochondriacs frequently see dark objects,\nsuch as threads, hairs, spiders, flies, wasps.\nThese appearances also exhibit themselves in\nthe incipient hard cataract. Many see semi-\ntransparent small tubes, forms like wings of\ninsects, bubbles of water of various sizes, which\nfall slowly down, if the eye is raised : some-\ntimes these congregate together so as to resem-\nble the spawn of frogs ; sometimes they appear\nas complete spheres, sometimes in the form of\nlenses.\n\nAs light appeared, in the former instances.\n\nPATHOLOGICAL COLOURS. 51\n\nwithout external light, so also these images\nappear without corresponding external objects.\nThe images are sometimes transient, sometimes\nthey last during the patient's life. Colour, again,\nfrequently accompanies these impressions : for\nhypochondriacs often see yellow-red stripes in\nthe eye: these are generally more vivid and\nnumerous in the morning, or when fasting.\n\nWe have before seen that the impression of\nany object may remain for a time in the eye :\nthis we have found to be a physiological phe-\nnomenon (23) : the excessive duration of such\nan impression, on the other hand, may be con-\nsidered as morbid.\n\nThe weaker the organ the longer the impres-\nsion of the image lasts. The retina does not so\nsoon recover itself; and the effect may be con-\nsidered as a kind of paralysis (28).\n\nThis is not to be wondered at in the case of\ndazzling lights. If any one looks at the sun, he\nmay retain the image in his eyes for several\ndays. Boyle relates an instance of ten years.\n\nThe same takes place, in acet\\.^Vxv^^%\\^^,^\\^\n\n52 PATHOLOGICAL COLOURS.\n\nregard to objects that are not dazzling. Biisch\nrelates of himself that the image of an engrav-\ning, complete in all its parts, was impressed on\nhis eye for seventeen minutes.\n\nA person inclined to fulness of blood retained\nthe image of a bright red calico, with white spots,\nmany minutes in the eye, and saw it float before\neverything like a veil. It only disappeared by\nrubbing the eye for some time.\n\nScherfer observes that the red colour, which is\nthe consequence of a powerful impression of\nlight, may last for some hours.\n\nAs we can produce an appearance of light on\nthe retina by pressure on the eyeball, so by a\ngentle pressure a red colour appears, thus cor-\nresponding with the after-image of an impression\nof light.\n\nMany sick persons, on awaking, see every-\nthing in the colour of the morning sky, as if\nthrough a red veil : so, if in the evening they\ndoze and wake again, the same appearance pre-\nsents itself. It remains for some minutes, and\n\nPATHOLOGICAL COLOURS. ^ 53\n\nalways disappears if the eye is rubbed a little.\nRed stars and balls sometimes accompany the\nimpression. This state may last for a consider-\nable time.\n\nThe aeronauts, particularly Zambeccari and\nhis companions, relate that they saw the moon\nblood-red at the highest elevation. As they had\nascended above the vapours of the earth, through\nwhich we see the moon and sun naturally of such\na colour, it may be suspected that this appear-\nance may be classed with the pathological co-\nlours. The senses, namely, may be so influenced\nby an unusual state, that the whole nervous\nsystem, and particularly the retina, may sink\ninto a kind of inertness and inexcitability.\nHence it is not impossible that the moon might\nact as a very subdued light, and thus produce\nthe impression of the red colour. The sun even\nappeared blood-red to the aeronauts of Ham-\nburgh.\n\nIf those who are at some elevation in a balloon\nscarcely hear each other speak, may not this,\ntoo, be attributed to the inexcitable state of the\nnerves as well as to the thinness of the air?\n\nObjects are often seen by sick persons in\nvariegated colours. Boyle relates aw vwsAaw^^\n\n54 PATHOLOGICAL COLOURS.\n\nof a lady, who, after a fall by which an eye was\nbruised, saw all objects, but especially white\nobjects, glittering in colours, even to an intoler-\nable degree.\n\nPhysicians give the name of \" Chrupsia\" to an\naffection of the sight, occurring in typhoid ma-\nladies. In these cases the patients state that\nthey see the boundaries of objects coloured where\nlight and dark meet. A change probably takes\nplace in the humours of the eye, through which\ntheir achromatism is affected.\n\nIn cases of milky cataract, a very turbid crys-\ntalline lens causes the patient to see a red light.\nIn a case of this kind, which was treated by the\napplication of electricity, the red light changed\nby degrees to yellow, and at last to white, when\nthe patient again began to distinguish objects.\nThese changes of themselves warranted the con-\nclusion that the turbid state of the lens was gra-\ndually approaching the transparent state. We\nshall be enabled easily to trace this effect to its\nsource as soon as we become better acquainted\nwith the physical colours.\n\nIf again it may be assumed that a jaundiced\n\nPATHOLOGICAL COLOURS. 55\n\npatient sees through an actually yellow-coloured\nhumour, we are at once referred to the depart-\nment of chemical colours, and it is thus evident\nthat we can only thoroughly investigate the\nchapter of pathological colours when we have\nmade ourselves acquainted with the whole range\nof the remaining phenomena. What has been\nadduced may therefore suffice for the present,\ntill we resume the further consideration of this\nportion of our subject.\n\nIn conclusion we may, however, at once ad-\nvert to some peculiar states or dispositions of\nthe organ.\n\nThere are painters who, instead of rendering\nthe colours of nature, diffuse a general tone, a\nwarm or cold hue, over the picture. In some,\nagain, a predilection for certain colours displays\nitself; in others a want of feeling for harmony.\n\nLastly, it is also worthy of remark, that sa-\nvage nations, uneducated people, and children\nhave a great predilection for vivid colours ; that\nanimals are excited to rage by certain colours ;\nthat people of refinement avoid vivid colours in\ntheir dress and the objects that are about them,\nand seem inclined to banish them altogether\nfrom their presence. — Note 1\n\nPART 11.\n\nPHYSICAL COLOURS.\n\nWe give this designation to colours which are\nproduced by certain material mediums : these\nmediums, however, have no colour themselves,\nand may be either transparent, semi-transpa-\nrent yet transmitting light, or altogether opaque.\nThe colours in question are thus produced in\nthe eye through such external given causes, or\nare merely reflected to the eye when by what-\never means they are already produced without\nus. Although we thus ascribe to them a certain\nobjective character, their distinctive quality still\nconsists in their being transient, and not to be\narrested.\n\nThey are called by former investigators co-\nhres apparentesy fluxiy fugitivi^ phantasticiy falsi^\nvariantes. They are also called speciosi and\nemphatici^ on account of their striking splen-\ndour. They are immediately connected with\nthe physiological colours, and appear to have\nbut little more reality : for, while in the produc-\n\nPHYSICAL COLOURS. 57\n\ntion of the physiological colours the eye itself\nwas chiefly efficient, and we could only perceive\nthe phenomena thus evoked within ourselves,\nbut not without us, we have now to consider\nthe fact that colours are produced in the eye by\nmeans of colourless objects ; that we thus too\nhave a colourless surface before us which is\nacted upon as the retina itself is, and that we\ncan perceive the appearance produced upon it\nwithout us. In such a process, however, every\nobservation will convince us that we have to do\nwith colours in a progressive and mutable, but\nnot in a final or complete^ state.\n\nHence, in directing our attention to these\nphysical colours, we find it quite possible to\nplace an objective phenomenon beside a sub-\njective one, and often by means of the union of\nthe two successfully to penetrate farther into\nthe nature of the appearance.\n\nThus, in the observations by which we become\nacquainted with the physical colours, the eye is\nnot to be considered as acting alone ; nor is the\nlight ever to be considered in immediate relation\nwith the eye : but we direct our attention espe-\ncially to the various effects produced by me-\ndiums, those mediums being themselves ^q\\q»>\\\\-\nless.\n\n•wA\n\n58 PHYSICAL COLOURS.\n\nLight under these circumstances may be af-\nfected by three conditions. First, when it\nflashes back from the surface of a medium ; in\nconsidering which cataptrical experiments invite\nour attention. Secondly, when it passes by the\nedge of a medium : the phenomena thus pro-\nduced were formerly called perioptical ; we pre-\nfer the term paroptical. Thirdly, when it passes\nthrough either a merely light-transmitting or an\nactually transparent body ; thus constituting a\nclass of appearances on which dioptrical expe-\nriments are founded. We have called a fourth\nclass of physical colours epoptical, as the pheno-\nmena exhibit themselves on the colourless sur-\nface of bodies under various conditions, without\nprevious or actual dye (fia^rji). — Note K.\n\nIn examining these categories with reference\nto our three leading divisions, according to\nwhich we consider the phenomena of colours\nin a physiological, physical, or chemical view,\nwe find that the catoptrical colours are closely\nconnected with the physiological ; the paropti-\ncal are already somewhat more distinct and\nindependent ; the dioptrical exhibit themselves\nas entirely and strictly physical, and as having\na decidedly objective character ; the epoptical,\nalthough still only apparent, may be considered\nas the transition to the chemical co\\owt%.\n\nDIOPTRICAL COLOURS. 59\n\nIf we were desirous of prosecuting our investi-\ngation strictly in the order of nature, we ought\nto proceed according to the classification which\nhas just been made ; but in didactic treatises it\nis not of so much consequence to connect as to\nduly distinguish the various divisions of a sub-\nject, in order that at last, when every single\nclass and case has been presented to the mind,\nthe whole may be embraced in one comprehen-\nsive view. We therefore turn our attention forth-\nwith to the dioptrical class, in order at once to\ngive the reader the full impression of the phy-\nsical colours, and to exhibit their characteristics\nthe more strikingly.\n\nIX.\n\nDIOPTRICAL COLOURS.\n\nColours are called dioptrical whetn a colour-\nless medium is necessary to produce them ; the\nmedium must be such that light and darkness\ncan act through it either on the eye or on oppo-\nsite surfaces. It is thus required that the me-\ndium should be transparent, or at least capable,\nto a certain degree, of transmitting light.\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nAccording to these conditions we divide the\ndioptrical phenomena into two classes, placing\nin the first those which are produced by means\nof imperfectly transparent, yet light-transmit-\nting mediums ; and in the second such as are\nexhibited when the medium is in the highest\ndegree transparent.\n\nX.\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nSpace, if we assume it to be empty, would\nhave the quality of absolute transparency to\nour vision. If this space is filled so that the\neye cannot perceive that it is so, there exists a\nmore or less material transparent medium,\nwhich may be of the nature of air and gas, may\nbe fluid or even solid.\n\n146,\n\nThe pure and light-transmitting semi-trans-\nparent medium is only an accumulated form of\nthe transparent medium. It may therefore be\npresented to us in three modes.\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS. 61\n\nThe extreme degree of this accumulation is\nwhite ; the simplest, brightest, first, opaque\n^ occupation of space.\n\nTransparency itself, empirically considered,\nis already the first degree of the opposite state.\nThe intermediate degrees from this point to\nopaque white are infinite.\n\nAt whatever point short of opacity we arrest\nthe thickening medium, it exhibits simple and\nremarkable phenomena when placed in relation\nwith light and darkness.\n\nThe highest degree of light, such as that of\nthe sun, of phosphorus burning in oxygen, is\ndazzling and colourless: so the light of the\nfixed stars is for the most part colourless. This\nlight, however, seen through a medium but very\nslightly thickened, appears to us yellow. If the\ndensity of such a medium be increased, or if its\nvolume become greater, we shall see the light\ngradually assume a yellow-red hue, which at\nlast deepens to a ruby-colour. — Note L.\n\n62 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nIf on the other hand darkness is seen through\na semi-transparent medium, which is itself illu-\nmined by a light striking on it, a blue colour\nappears : this becomes lighter and paler as the\ndensity of the medium is increased, but on the\ncpntrary appears darker and deeper the more\ntransparent the medium becomes : in the least\ndegree of dimness short of absolute transpa-\nrence, always supposing a perfectly colourless\nmedium, this deep blue approaches the most\nbeautiful violet.\n\nIf this effect takes place in the eye as here de-\nscribed, and may thus be pronounced to be sub-\njective, it remains further to convince ourselves\nof this by objective phenomena-. For a light\nthus mitigated and subdued illumines all objects\nin like manner with a yellow, yellow-red, or\nred hue; and, although the effect of darkness\nthrough the non-transparent medium does not\nexhibit itself so powerfully, yet the blue sky\ndisplays itself in the camera obscura very dis-\ntinctly on white paper, as well as every other\ninaterial colour.\n\nIn examining the cases in which this impor-\n\nDIOFTBICAL COLOURS OF THE FIRST CLASS. 63\n\ntant leading phenomenon appears, we naturally\nmention the atmospheric colours first : most of\nthese may be here introduced in order.\n\nThe sun seen through a certain degree of\nvapour appears with a yellow disk ; the centre\nis often dazzlingly yellow when the edges are\nalready red. The orb seen through a thick\nyellow mist appears ruby-red (as was the case\nin 1 794, even in the north) ; the same appear-\nance is still more decided, owing to the state of\nthe atmosphere, when the scirocco prevails in\nsouthern climates: the clouds generally sur-\nrounding the sun in the latter case are of the\nsame colour, which is reflected again on all\nobjects.\n\nThe red hues of morning and evening are\nowing to the same cause. The sun is announced\nby a red light, in shining through a greater mass\nof vapours. The higher he rises, the yellower\nand brighter the light becomes.\n\nIf the darkness of infinite space is seen through\natmospheric vapours illumined by the day-light,\nthe blue colour appears. On high mountains\nthe sky appears by day intensely blue, owing to\nthe few thin vapours that float before the end-\nless dark space : as soon as we descend vcv \\X\\^\n\n64 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nvalleys, the blue becomes lighter ; till at last, in\ncertaiu regions, and in consequence of increasing\nvapours, it altogether changes to a very pale\nblue.\n\nThe mountains, in like manner, appear to us\nblue ; for, as we see them at so great a distance\nthat we no longer distinguish the local tints,\nand as no light reflected from their surface acts\non our vision, they are equivalent to mere dark\nobjects, wliich, owing to the interposed vapours,\nappear blue.\n\nSo we find the shadowed parts of nearer ob-\njects are blue when the air is charged with thin\nvapours.\n\nThe snow-mountains, on the other hand, at a\ngreat distance, still appear white, or approaching\nto a yellowish hue, because they act on our eyes\nas brightness seen through atmospheric vapour.\n\nThe blue appearance at the lower part of the\nflame of a candle belongs to the same class of\nphenomena. If the flame be held before a whke\nground, no blue will be seen, but this colour\nwill immediately appear if the flame is opposed\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS. 65\n\nto a black ground. This phenomenon may be\nexhibited most strikingly with a spoonful of\nlighted spirits of wine. We may thus consider\nthe lower part of the flame as equivalent to the\nvapour which, although infinitely thin, is still\napparent before the dark surface ; it is so thin,\nthat one may easily see to read through it : on\nthe other hand, the point of the flame which\nconceals objects from our sight is to be consi-\ndered as a self-illuminating body.\n\nLastly, smoke is also to be considered as a\nsemi-transparent medium, which appears to us\nyellow or reddish before a light ground, but blue\nbefore a dark one.\n\nIf we now turn our attention to fluid mediums,\nwe find that water, deprived in a very slight\nd^ree of its transparency, produces the same\nefiects.\n\nThe infusion of the lignum nephriticum (gui-\nlandina Linnaei), which formerly excited so much\nattention, is only a semi-transparent liquor,\nwhich in dark wooden cups must appear blue,\nbut held towards the sun in a transparent glass\nmust exhibit a yellow appearauce.\n\n66 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nA drop of scented water, of spirit varnish, of\nseveral metallic solutions, may be employed to\ngive various degrees of opacity to water for such\nexperiments. Spirit of soap perhaps answers\nbest.\n\nThe bottom of the sea appears to divers of a\nred colour in bright sunshine : in this case the\nwater, owing to its depth, acts as a semi-trans-\nparent medium. Under these circumstances,\nthey find the shadows green, which is the com-\nplemental colour.\n\nAmong solid mediums the opal attracts our\nattention first: its colours are, at least, partly\nto be explained by the circumstance that it is,\nin fact, a semi-transparent medium, through\nwhich sometimes light, sometimes dark, sub-\nstrata are visible.\n\nFor these experiments, however, the opal-\nglass (vitrum astroides, girasole) is the most\ndesirable material. It is prepared in various\nways, and its semi-opacity is produced by me-\ntallic oxydes. The same efiect is produced also\nby melting pulverised and calcined bones toger\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS. 67\n\nther with the glass^ oii which account it is also\nknown by the name of beinglas ; but, prepared\nin this mode, it easily becomes too opaque.\n\nThis glass may be adapted for experiments in\nvarious ways : it may either be made in a very\nslight degree non-transparent, in which case the\nlight seen through various layers placed one\nupon the other may be deepened from the lightest\nyellow to the deepest red, or, if made originally\nmore opaque, it may be employed in thinner or\nthicker laminae. The experiments may be suc-\ncessfully made in both ways :f in order, however,\nto see the bright blue colour^Hhe glass should\nneither be too opaque nor too thick. For, as it\nis quite natural that darkness must act weakly\nthrough the semi-transparent medium, so this\nmedium, if too thick, soon approaches whiteness.\n\nPanes of glass throw a yellow light on objects\nthrough those parts where they happen to be\nsemi-opaque, and these same parts appear blue\nif we look at a dark object through them.\n\nSmoked glass may be also mentioned here,\nand is, in like manner, to be considered as a\nsemi-opaque medium. It exhibits lV\\e ^wev \\xv^\\^\n\n68 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nor less ruby- coloured ; and, although this appear-\nance may be attributed to the black-brown\ncolour of the soot, we may still convince our-\nselves that a semi-transparent medium here acts\nif we hold such a glass moderately smoked, and\nlit by the sun on the unsmoked side, before a\ndark object, for we shall then perceive a bluish\nappearance.\n\nA striking experiment may be made in a\ndark room with sheets of parchment. If we\nfasten a piece of parchment before the opening\nin the window-shutter when the sun shines, it\nwill appear nearly white ; by adding a second,\na yellowish colour appears, which still increases\nas more leaves are added, till at last it changes\nto red.\n\nA similar effect, owing to the state of the\ncrystalline lens in milky cataract, has been\nalready adverted to (131).\n\nHaving now, in tracing these phenomena,\narrived at the effect of a degree of opacity\nscarcely capable of transmitting light, we may\nhere mention a singular appearance which was\nowing to a momentary state of this kind.\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS. 69\n\nA portrait of a celebrated theologian had\nbeen painted some years before the circum-\nstance to which we allude, by an artist who\nwas known to have considerable skill in the\nmanagement of his materials. The very reve-\nrend individual was represented in a rich velvet\ndress, which was not a little admired, and which\nattracted the eye of the spectator almost more\nthan the face. The picture, however, from the\neffect of the smoke of lamps and dust, had lost\nmuch of its original vivacity. It was, therefore,\nplaced in the hands of a painter, who was to\nclean it, and give it a fresh coat of varnish.\nThis person began his operations by carefully\nwashing the picture with a sponge : no\nsooner, however, had he gone over the surface\nonce or twice, and wiped away the first dirt,\nthan to his amazement the black velvet dress\nchanged suddenly to a light blue plush, which\ngave the ecclesiastic a very secular, though some-\nwhat old-fashioned, appearance. The painter\ndid not venture to go on with his washing : he\ncould not comprehend how a light blue should\nbe the ground of the deepest black, still less\nhow he could so suddenly have removed a glaz-\ning colour capable of converting the one tint\nto the other.\n\nAt all events, he was not a little disconcerted\nat having spoilt the picture to such an exteut.\nNothing to characterize the eecXe^x^'SsVvc \\^-\n\n70 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nmained but the richly-curled round wig, which\nmade the exchange of a faded plush for a hand-\nsome new velvet dress far from desirable.\nMeanwhile, the mischief appeared irreparable,\nand the good artist, having turned the picture to\nthe wall, retired to rest with a mind ill at ease.\nBut what was his joy the next morning, when,\non examining the picture, he beheld the black\nvelvet dress again in its full splendour. He\ncould not refrain from again wetting a corner,\nupon which the blue colour again appeared, and\nafter a tim6 vanished. On hearing of this phe-\nnomenon,* I went at once to see the miraculous\npicture. A wet sponge was passed over it in\nmy presence, and the change quickly took place.\nI saw a somewhat faded, but decidedly light\nblue plush dress, the folds under the arm being\nindicated by some brown strokes.\n\nI explained this appearance to myself by the\ndoctrine of the semi-opaque medium. The\npainter, in order to give additional depth to his\nblack, may have passed some particular varnish\nover it : on being washed, this varnish imbibed\nsome moisture, and hence became semi-opaque,\nin consequence of which the black underneath\nimmediately appeared blue. Perhaps those\nwho are practically acquainted with the effect\nof varnishes may, through accident or con-\ntrivance, arrive at some means of exhibiting this\nsingular appearance, as an experiment, to those\n\nDIOPTRICAL COLOURS OF THE FULST CLASS. 71\n\nwho are fond of investigating natural pheno-\nmena. Notwithstanding many attempts, I\ncould not myself succeed in re-producing it.\n\nHaving now traced the most splendid in-\nstances of atmospheric appearances, as well as\nother less striking yet sufficiently remarkable\ncases, to the leading examples of semi-trans-\nparent mediums, we have no doubt that atten-\ntive observers of nature will carry such re-\nsearches further, and accustom themselves to\ntrace and explain the various appearances\nwhich present themselves in every-day experi-\nence on the same principle : we may also hope\nthat such investigators will provide themselves\nwith an adequate apparatus in order to place\nremarkable facts before the eyes of others who\nmay be desirous of information.\n\nWe venture, once for all, to call the leading\nappearance in question, as generally described\nin the foregoing pages, a primordial and ele-\nmentary phenomenon ; and we may here be\npermitted at once to state what we understand\nby the term.\n\nThe circumstances which come under our notice\nin ordinary observation are, for the most part, in-\nsulated cases, which, with some aUew\\\\ow, ^^\\»\\\\.\n\n72 DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\nof being classed under general leading facts.\nThese again range themselves under theoretical\nrubrics which are more comprehensive, and\nthrough which we become better acquainted\nwith certain indispensable conditions of appear-\nances in detail. From henceforth everything is\ngradually arranged under higher rules and laws,\nwhich, however, are not to be made intelligible\nby words and hypotheses to the understanding\nmerely, but, at the same time, by real phenomena\nto the senses. We call these primordial phe-\nnomena, because nothing appreciable by the\nsenses lies beyond them, on the contrary, they\nare perfectly fit to be considered as a fixed point\nto which we first ascended, step by step, and\nfrom which we may, in like manner, descend to\nthe commonest case of every-day experience.\nSuch an original phenomenon is that which has\nlately engaged our attention. We see on the\none side light, brightness ; on the other dark-\nness, obscurity : we bring the semi-transparent\nmedium between the two, and from these con-\ntrasts and this medium the colours develop\nthemselves, contrasted, in like manner, but soon,\nthrough a reciprocal relation, directly tending\nagain to a point of union.'*'\n\n* That is (according to the author's statement 150. 151.) both\ntend to red ; the yellow deepening to orange as the comparatively\ndark medium is thickened before brightness ; the blue deepening\nto violet SB the light medium is thinned before darkness. — ^T.\n\nDIOPTRICAL COLOURS OF THE FIRST CLASS. 73\n\nWith this coDviction we look upon the mistake\nthat has been committed in the investigation of\nthis subject to be a very serious one, inasmuch\nas a secondary phenomenon has been thus\nplaced higher in order — the primordial phe-\nnomenon has been degraded to an inferior place ;\nnay, the secondary phenomenon has been placed\nat the head, a compound effect has been treated\nas simple, a simple appearance as compound :\nowing to this contradiction, the most capricious\ncomplication and perplexity have been intro-\nduced into physical inquiries, the effects of\nwhich are still apparent.\n\nBut when even such a primordial phenomenon\nis arrived at, the evil still is that we refuse to\nrecognise it as such^ that we still aim at some-\nthing beyond, although it would become us to\nconfess that we are arrived at the limits of ex-\nperimental knowledge. Let the observer of\nnature suffer the primordial phenomenon to re-\nmain undisturbed in its beauty; let the phi-\nlosopher admit it into his department, and he\nwill find that important elementary facts are a\nworthier basis for further operations than insu-\nlated cases, opinions, and hypotheses. — Note M.\n\n74 DIOPTRICAL COLOUBS\n\nXI.\n\nDIOPTRICAL COLOURS OF THE SECOND CLASS.-~REFRAC.\n\nTION.\n\nDioptrical colours of both classes are closely\nconnected^ as will presently appear on a little\nexamination. Those of the first class appeared\nthrough semi-transparent mediums^ those of the\nsecond class will now appear through transparent\nmediums. But since every substance, however\ntransparent, may be already considered to par-\ntake of the opposite quality (as every accumula-\ntion of a medium called transparent proves),\nso the near affinity of the two classes is suffi-\nciently manifest.\n\nWe will, however, first consider transparent\nmediums abstractedly as such, as entirely free\nfrom any degree of opacity, and direct our\nwhole attention to a phenomenon which here\npresents itself, and which is known by the name\nof refraction.\n\nIn treating of the physiological colours, we\nhave already had occasion to vindicate what\nwere fovmerXy called illusions of sight, as the\n\nOF THE SECOND CLASS.— REFRACTION. 75\n\nactive energies of the healthy and duly efficient\neye (2), and we are now again invited to con-\nsider similar instances confirming the constancy\nof the laws of vision.\n\nThroughout nature, as presented to the senses,\neverything depends on the relation which things\nbear to each other, but especially on the relation\nwhich man, the most important of these, bears\nto the rest. Hence the world divides itself into\ntwo parts, and the human being as subject, stands\nopposed to the object. Thus the practical\nman exhausts himself in the accumulation of\nfacts, the thinker in speculation ; each being\ncalled upon to sustain a conflict which admits\nof no peace and no decision.\n\nBut still the main point always is, whether\nthe relations are truly seen. As our senses, if\nhealthy, are the surest witnesses of external re-\nlations, so we may be convinced that, in all in-\nstances where they appear to contradict reality,\nthey lay the greater and surer stress on true\nrelations. Thus a distant object appears to us\nsmaller ; and precisely by this means we are\naware of distance. We produced coloured ap-\npearances on colourless objects, through colour-\nless mediums^ and at the same motcievvV wvc ^V-\n\n76 DIOPTRICAL COLOURS\n\ntention was called to the degree of opacity in\nthe medium.\n\nThus the different degrees of opacity in so-\ncalled transparent mediums, nay, even other\nphysical and chemical properties belonging to\nthem, are known to our vision by means of re-\nfraction, and invite us to make further trials in\norder to penetrate more completely by physical\nand chemical means into those secrets which are\nalready opened to our view on one side.\n\nObjects seen through mediums more or less\ntransparent do not appear to us in the place\nwhich they should occupy according to the laws\nof perspective. On this fact the dioptrical\ncolours of the second class depend.\n\nThose laws of vision which admit of being\nexpressed in mathematical formulae are based on\nthe principle that, as light proceeds in straight\nlines, it must be possible to draw a straight line\nfrom the eye to any given object in order that it\nbe seen. If, therefore, a case arises in which\nthe light arrives to us in a bent or broken line,\nthat we see the object by means of a bent or\nbroken line, we are at once informed that the\n\nOP THE SECOND CLASS.— REFRACTION. 77\n\nmedium between the eye and the object is\ndenser, or that it has assumed this or that\nforeign nature.\n\nThis deviation from the law of right-lined\nvision is known by the general term of refrac-\ntion ; and, although we may take it for granted\nthat our readers are sufficiently acquainted with\nits effects, yet we will here once more briefly\nexhibit it in its objective and subjective point\nof view.\n\nLet the sun shine diagonally into an empty\ncubical vessel, so that the opposite side be il-\nlumined, but not the bottom : let water be then\npoured into this vessel, and the direction of the\nlight will be immediately altered ; for a part of\nthe bottom is shone upon. At the point where\nthe light enters the thicker medium it deviates\nfrom its rectilinear direction, and appears broken :\nhence the phenomenon is called the breaking\n(brechung) or refraction. Thus much of the\nobjective experiment\n\nWe arrive at the subjective fact in the follow-\ning mode : — Let the eye be substituted for the\nsun : let the sight be directed iu like \\xv^\\i\\i<^\\:\n\n\"• 1 T n^j\"*\n\n78 DIOPTRICAL COLOURS\n\ndiagonally over one side, so that the opposite\ninner side be entirely seen, while no part of the\nbottom is visible. On pouring in water the eye\nwill perceive a part of the bottom ; and this takes\nplace without our being aware that we do not\nsee in a straight line ; for the bottom appears to\nus raised, and hence we give the term elevation\n(hebung) to the subjective phenomenon. Some\npoints, which are particularly remarkable with\nreference to this, will be adverted to hereafter.\n\nWere we now to express this phenomenon\ngenerally, we might here repeat, in conformity\nwith the view lately taken, that the relation of\nthe objects is changed or deranged.\n\nBut as it is our intention at present to separate\nthe objective from the subjective appearances,\nwe first express the phenomenon in a subjective\nform, and say, — a derangement or displacement\nof the object seen, or to be seen, takes place.\n\nBut that which is seen without a limiting out-\nline maybe thus afiected without our perceiving\nthe change. On the other hand, if what we look\nat has a visible termination, we have an evident\nindication that a displacement occurs. If, there-\n\nOP THE SECOND CLASS.— REFRACTION. 79\n\nfore, we wish to ascertain the relation or degree\nof such a displacement, we must chiefly confine\nourselves to the alteration of surfaces with visible\nboundaries ; in other words, to the displacement\nof circumscribed objects.\n\nThe general efiect may take place through\nparallel mediums, for every parallel medium\ndisplaces the object by bringing it perpendi-\ncularly towards the eye. The apparent change\nof position is, however, more observable through\nmediums that are not parallel.\n\nThese latter may be perfectly spherical, or\nmay be employed in the form of convex or con-\ncave lenses. We shall make use of all these as\noccasion may require in our experiments. But\nas they not only displace the object from its po-\nsition, but alter it in various ways, we shall, in\nmost cases, prefer employing mediums with sur-\nfaces, not, indeed, parallel with reference to each\nother, but still altogether plane, namely, prisms.\nThese have a triangle for their base, and may,\nit is true, be considered as portions of a lens,\nbut they are particularly available for our ex-\nperiments, inasmuch as they very perceptibly\ndisplace the object from its position, without\nproducing a remarkable distortion.\n\nREFRACTION WITHOUT\n\nAnd now, in order to conduct our observations\nwith as much exactness as possible, and to avoid\nall confusion and ambiguity, we confine ourselves\nat first to\n\nSUBJECTIVE EXPERIMENTS,\n\nin which, namely, the object is seen by the ob-\nserver through a refracting medium. As soon\nas we have treated these in due series, the ob-\njective experiments will follow in similar order.\n\nXII.\n\nREFRACTION WITHOUT THE APPEARANCE OF COLOUR.\n\nRefraction can visibly take place without our\nperceiving an appearance of colour. To what-\never extent a colourless or uniformly coloured\nsurface may be altered as to its position by re-\nfraction, no colour consequent upon refraction\nappears within it, provided it has no outline or\nboundary. We may convince ourselves of this\nin various ways.\n\nTHE APPEARANCE OF COLOUR. 81\n\nPlace a glass cube on any larger surface,\nand look through the glass perpendicularly or\nobliquely, the unbroken surface opposite the eye\nappears altogether raised, but no colour exhibits\nitself. If we look at a pure grey or blue sky or\na uniformly white or coloured wall through a\nprism, the portion of the surface which the eye\nthus embraces will be altogether changed as to\nits position, without our therefore observing the\nsmallest appearance of colour.\n\nXIII.\n\nCONDITIONS OF THE APPEARANCE OF COLOUR.\n\nAlthough in the foregoing experiments we\nhave found all unbroken surfaces, large or small,\ncolourless, yet at the outlines or boundaries,\nwhere the surface is relieved upon a darker or\nlighter object, we observe a coloured appearance.\n\nOutline, as well as surface, is necessary to\nconstitute a figure or circumscribed object. We\ntherefore express the leading fact thus : circum-\nscribed objects must be displaced by refraction\nin order to the exhibition of an appearance of\ncolour. '\n\n82 CONDITIONS OF\n\nWe place before us the simplest object, a light\ndisk on a dark ground (a).* A displacement\noccurs with regard to this object, if we appa-\nrently extend its outline from the centre by mag-\nnifying it. This may be done with any convex\nglass, and in this case we see a blue edge (b).\n\nWe can, to appearance, contract the circum-\nference of the same light disk towards the centre\nby diminishing the object ; the edge will then\nappear yellow (c). This may be done with a\nconcave glass, which, however, should not be\nground thin like common eye-glasses, but must\nhave some substance. In order, however, to\nmake this experiment at once with the convex\nglass, let a smaller black disk be inserted within\nthe light disk on a black ground. If we magnify\nthe black disk on a white ground with a con-\nvex glass, the same result takes place as if we\ndiminished the white disk ; for we extend the\nblack outline upon the white, and we thus per-\nceive the yellow edge together with the blue\nedge (d).\n\nThese two appearances, the blue and yellow,\nexhibit themselves in and upon the white : they\n\n♦ Plate 2. fig. 1 .\n\nTHE APPEARANCE OF COLOUR. 83\n\nboth assume a reddish hue, in proportion as\nthey mingle with the black.*\n\nIn this short statement we have described the\nprimordial phenomena of all appearance of co-\nlour occasioned by refraction. These undoubt-\nedly may be repeated, varied, and rendered\nmore striking ; may be combined, complicated,\nconfused ; but, after all, may be still restored\nto their original simplicity.\n\nIn examining the process of the experiment\njust given, we find that in the one case we have,\nto appearance^ extended the white edge upon the\ndark surface ; in the other we have extended the\ndark edge upon the white surface, supplanting\none by the other, pushing one over the other.\nWe will now endeavour, step by step, to analyse\nthese and similar cases.\n\nIf we cause the white disk to move, in appear-\nance, entirely from its place, which can be done\n\n■ ■ ■ ' II. , . . I 11 ,\n\n* The author has omitted the orange and purple in the co-\nloured diagrams which illustrate these first experiments, from a\nwish probably to present the elementary contrast, on which he\nlays a stress, in greater simplicity. The reddish tinge would . be\napparent, as stated above, where the blue and yellow are in con-\ntact with the black. — T.\n\n84 CONDITIONS OF\n\neflfectually by prisms, it will be coloured ac-\ncording to the direction in which it apparently\nmoves, in conformity with the above laws. If\nwe look at the disk a* through a prism, so that\nit appear moved to i, the outer edge will\nappear blue and blue-red, according to the law\nof the figure b (fig. 1), the other edge being\nyellow, and yellow-red, according to the law of\nthe figure c (fig. 1). For in the first case the\nwhite figure is, as it were, extended over the\ndark boundary, and in the other case the dark\nboundary is passed over the white figure. The\nsame happens if the disk is, to appearance,\nmoved from a to c, from a to rf, and so throughout\nthe circle.\n\nAs it is with the simple effect, so it is with\nmore complicated appearances. If we look\nthrough a horizontal prism (aJf ) at a white disk\nplaced at some distance behind it at ^, the disk\nwill be raised to /, and coloured according to\nthe above law. If we remove this prism, and\nlook through a vertical one (c d) at the same\ndisk, it will appear at A, and coloured accord-\ning to the same law. If we place the two\nprisms one upon the other, the disk will appear\ndisplaced diagonally, in conformity with a ge-\nneral law of nature, and will be coloured as\n\n* Plate 2, fig. 2. t Plate 2, fig. 4.\n\nTHE APPEARANCE OF COLOUR. 85\n\nbefore; that is, according to its movement in the\ndirection, e. g. : *\n\nIf we attentively examine these opposite co-\nloured edges, we find that they only appear in\nthe direction of the apparent change of place.\nA round figure leaves us in some degree uncer-\ntain as to this : a quadrangular figure removes\nall doubt.\n\nThe quadrangular figure a,t moved in the\ndirection ab, or aef, exhibits no colour on the\nsides which are parallel with the direction in\nwhich it moves : on the other hand, if moved\nin the direction ac, parallel with its diagonal,\nall the edges of the figure appear coloured. J\n\nThus, a former position (203) is here con-\nfirmed; viz. to produce colour, an object must\nbe so displaced that the light edges be appa-\nrently carried over a dark surface, the dark\nedges over a light surface, the figure over its\nboundary, the boundary over the figure. But\n\n* In this case, according to the author, the refracting medium\nbeing increased in mass, the appearance of colour is increased,\nand the displacement is greater. — T.\n\nt Plate 2, fig. 3.\n\nJ Fig. 2, plate 1, contains a variety of forms, which, when\nviewed through a prism, are intended to illufitt«Aj& iVv^ ^\\A\\j^tDAx^.\nin this and the following paragraph.\n\n86 CONDITIONS UNDER WHICH THE\n\nif the rectilinear boundaries of a figure could be\nindefinitely extended by refraction, so that figiure\nand background might only pursue their course\nnext, but not over each other, no colour would\nappear, not even if they were prolonged to\ninfinity.\n\nXIV.\n\nCONDITIONS UNDER WHICH THE APPEARANCE OF\n\nCOLOUR INCREASES.\n\nWe have seen in the foregoing experiments\nthat all appearance of colour occasioned by re-\nfraction depends on the condition that the\nboundary or edge be moved in upon the object\nitself, or the object itself over the ground, that\nthe figure should be, as it were, carried over\nitself, or over the ground. And we shall now\nfind that, by increased displacement of the object,\nthe appearance of colour exhibits itself in ^\ngreater degree. This takes place in subjective\nexperiments, to which, for the present, we con-\nfine ourselves, under the following conditions.\n\nFirst, if, in looking through parallel mediums,\nthe eye is directed more obliquely.\n\nSecondly, if the surfaces of the medium are\nno longer parallel, but form a more or less acute\n\nAPPEARANCE OF COLOUR INCREASES. 87\n\nThirdly, owing to the increased proportion of\nthe medium, whether parallel mediums be in-\ncreased in size, or whether the angle be in^\ncreased, provided it does not attain a right angle.\n\nFourthly, owing to the distance of the eye\narmed with a refracting medium from the object\nto be displaced.\n\nFifthly, owing to a chemical property that\nmay be communicated to the glass, and which\nmay be afterwards increased in effect.\n\nThe greatest change of place, short of consi-\nderable distortion of the object, is produced by\nmeans of prisms, and this is the reason why the\nappearance of colour can be exhibited most\npowerfully through glasses of this form. Yet\nwe will not, in employing them, suffer ourselves\nto be dazzled by the splendid appearances they\nexhibit, but keep the above well-established«\nsimple principles calmly in view.\n\nThe colour which is outside, or foremost, in\nthe apparent change of an object by refraction,\nis always the broader, and we will henceforth\ncall this a border : the colour that remains next\nthe outline is the narrower, and this we will call\nan edge.\n\n88 CONDITIONS UNDER WHICH THE\n\nIf we move a dark boundary towards a light\nsurface, the yellow broader border is- foremost,\nand the narrower yellow-red edge follows close\nto the outline. If we move a light boundary\ntowards a dark surface, the broader violet border\nis foremost, and the narrower blue edge follows.\n\nIf the object is large, its centre remains un-\ncoloured. Its inner surface is then to be consi-\ndered as unlimited (195) : it is displaced, but\nnot otherwise altered : but if the object is so\nnarrow, that under the above conditions the\nyellow border can reach the blue edge, the space\nbetween the outlines will be entirely covered\nwith colour. If we make this experiment with\na white stripe on a black ground,* the two ex-\ntremes will presently meet, and thus produce\ngreen. We shall then see the following series\nof colours : —\n\nYellow-red.\n\nYellow.\n\nGreen.\n\nBlue.\n\nBlue-red.\n\nIf we place a black band, or stripe, on white\npaper,t the violet border will spread till it meets\n\n♦ Plate 2, dg. 5, left. t Plate 2, fig. 5, nght.\n\n^. ..^. ■»' .0 rtm ■\n\nAPPEARANCE OF COLOUR INCREASES. 89\n\nthe yellow-red edge. In this case the inter-\nmediate black is effaced (as the intermediate\nwhite was in the last experiment), and in its\nstead a splendid pure red will appear.* The\nseries of colours will now be as follows : —\n\nBlue.\n\nBlue-red.\n\nRed.\n\nYellow-red.\n\nYellow.\n\nThe yellow and blue, in the first case (214),\ncan by degrees meet so fully, that the two\ncolours blend entirely in green, and the order\nwill then be.\n\nYellow-red.\nGreen.\nBlue-red.\nIn the second case (215), under similar cir-\ncumstances, we see only\n\nBlue.\nRed.\nYellow.\nThis appearance is best exhibited by refract-\ning the bars of a window when they are relieved\non a grey sky.f\n\n* This pure red, the union of orange and violet, is considered\nby the author the maximum of the coloured appearance : he has\nappropriated the term purpur to it. See paragraph 703, and\nnote.—T.\n\nt The bands or stripes in fig. 4, plate \\, 'w\\\\«a Vi^-^^ ^\\wy^^\nB prism, exhibit the colours represented in p\\%X^ % ii%^ ^.\n\ndo EXPLANATION OF THE FOREGOING PHENOMENA.\n\nIn all this we are never to forget that this\nappearance is not to be considered as a complete\nor final state, but always as a progressive, in-\ncreasing, and, in many senses, controllable ap-\npearance. Thus we find that, by the negation\nof the above five conditions, it gradually de-\ncreases, and at last disappears altogether.\n\nXV.\n\nEXPLANATION OF THE FOREGOING PHENOMENA.\n\nBefore we proceed further, it is incumbent on\nus to explain the first tolerably simple pheno-\nmenon, and to show its connexion with the\nprinciples first laid down, in order that the ob-\nserver of nature may be enabled clearly to com-\nprehend the more complicated appearances that\nfollow.\n\nIn the first place, it is necessary to remember\nthat we have to do with circumscribed objects.\nIn the act of seeing, generally, it is the circum-\nscribed visible which chiefly invites our obser-\nvation; and in the present instance, in speak-\ning of the appearance of colour, as occasioned\nhy refraction, the circumscribed visible, the de-\ntached object solely occupies ox^t ^UewvXow,\n\nEXPLANATION OF TH£ FOREGOING PHENOMENA. 91\n\nFcf our chromatic exhibitions we can, how-\never, divide objects generally into primary and\nsecondary. The expressions of themselves de-\nnote what we understand by them, but our\nmeaning will be rendered still more plain by\nwhat follows.\n\nPrimary objects may be considered firstly as\noriginal, as images which are impressed on the\neye by things before it, and which assure us of\ntheir reality. To these the secondary images\nmaybe opposed as derived images, which remain\nin the organ when the object itself is taken\naway ; those apparent after-images, which have\nbeen circumstantially treated of in the doctrine\nof physiological colours.\n\nThe primary images^ again, may be consi-\ndered as direct images, which, like the original\nimpressions, are conveyed immediately from the\nobject to the eye. In contradistinction to these,\nthe secondary images may be considered as i/t-\ndirect^ being only conveyed to us, as it were, at\nsecond-hand from a reflecting surface. These\nare the mirrored, or catoptrical, images, which\nin certain cases can also become double images:\n\nWhen, namely, the reflecting body \\& U\\i\\\\%-\n\n92 EXPLANATION OF TH£ FOREGOING PHENOMENA.\n\nparent, and has two parallel surfaces, one behind\nthe other : in such a case, an image may be re-\njected to the eye from both surfaces, and thus\narise double images, inasmuch as the upper\nimage does not quite cover the under one : this\nmay take place in various ways.\n\nLet a playing-card be held before a mirror.\nWe shall at first see' the distinct image of the\ncard, but the edge of the whole card, as well as\nthat of every spot upon it, will be bounded on\none side with a border, which is the beginning\nof the second reflection. This effect varies in\ndifferent mirrors, according to the different\nthickness of the glass, and the accidents of\npolishing. If a person wearing a white waist-\ncoat, with the remaining part of his dress dark,\nstands before certain mirrors, the border appears\nvery distinctly, and in like manner the metal\nbuttons on dark cloth exhibit the double reflec-\ntion very evidently.\n\nThe reader who has made himself acquainted\nwith our former descriptions of experiments (80)\nwill the more readily follow the present state-\nment. The window-bars reflected by plates of\nglass appear double, and by increased thickness\nof the glass, and a due adaptation of the angle\nof reflection, the two reflections may be entirely\nseparated from each other. So a vase full of\n\nEXPLANATION OF THE FOREGOING PHENOMENA. 93\n\nwater, with a plane mirror-like bottom, reflects\nany object twice, the two reflections being\nmore or less separated under the same con-\nditions. In these cases it is to be observed that,\nwhere the two reflections cover each other,\nthe perfect vivid image is reflected, but where\nthey are separated' they exhibit only weak,\ntransparent, and shadowy images.\n\nIf we wish to know which is the under and\nwhich the upper image, we have only to take a\ncoloured medium, for then a light object re-\nflected from the under surface is of the colour\nof the medium, while that reflected from the\nupper surface presents the complemental colour.\nWith dark objects it is the reverse ; hence black\nand white surfaces may be here also conveni-\nently employed. How easily the double images\nassume and evoke colours will here again be\nstriking.\n\nThirdly, the primary images may be con-\nsidered as principal images, while the secondary\ncan be, as it were, annexed to these as accessary\nimages. Such an accessory image produces a sort\nof double form ; except that it does not separate\nitself from the principal object, although it may\nbe said to be always endeavouring to do *o» ltv%\n\n94 EXPLANATION OF THE FOREQOINO PHENOMENA.\n\nwith secoudary images of this last description\nthat we have to do in prismatic appearances.\n\nA surface without a boundary exhibits no\nappearance of colour when refracted (195).\nWhatever is seen must be circumscribed by an\noutline to produce this effect. In other words\na figure, an object, is required ; this object\nundergoes an apparent change of place by re-\nfraction : the change is however not complete,\nnot clean, not sharp ; but incomplete, inasmuch\nas an accessory image only is produced.\n\nIn examining every appearance of nature,\nbut especially in examining an important and\nstriking one, we should not remain in one spot,\nwe should not confine ourselves to the insulated\nfact, nor dwell on it exclusively, but look round\nthrough all nature to see where something simi-\nlar, something that has affinity to it, appears :\nfor it is only by combining analogies that we\ngradually arrive at a whole which speaks for\nitself, and requires no further explanation.\n\nThus we here call to mind that in certain\ncases refraction unquestionably produces double\nimages, as is the case in Iceland spar : similar\n\nEXPLANATION OF THE FOREGOING PHENOMENA. 95\n\ndouble images are also apparent in cases of re-\nfraction through large rock crystals, and in\nother instances ; phenomena which have not\nhitherto been sufficiently observed.*\n\nBut since in the case under consideration\n(227) the question relates not to double but to\naccessory images^ we refer to a phenomenon\nalready adverted to, but not yet thoroughly\ninvestigated. We allude to an earlier experi-\nment, in which it appeared that a sort of con-\nflict took place in regard to the retina between\na light object and its dark ground, and between\na dark object and its light ground (16). The\nlight object in this case appeared larger, the\ndark one smaller.\n\nBy a more exact observation of this pheno-\nmenon we may remark that the forms are not\nsharply distinguished from the grpund, but that\nthey appear with a kind of grey, in some de-\ngree, coloured edge ; in short, with an accessory\nimage. If, then, objects seen only with the\nnaked eye produce such effects, what may not\ntake place when a dense medium is interposed?\nIt is not that alone which presents itself to us\n\n• The date of the publication, 1810, is sometimes to be remem-\nbered.— T.\n\niaifti\n\n06 EXPLANATION OF THE FOREQOINa PHEtCDMENA.\n\nin obvious operation which produces and suffers\neffects, but likewise all principles that have a\nmutual relation only of some sort are efficient\naccordingly, and indeed often in a very high\ndegree.\n\nThus when refraction produces its effect on\nan object there appears an accessory image\nnext the object itself: the real form thus re-\nfracted seems even to linger behind, as if resist-\ning the change of place ; but the accessory image\nseems to advance, and extends itself more or\nless in the mode already shown (212 — 216).\n\nWe also remarked (224) that in double\nimages the fainter appear only half substan-\ntial, having a kind of transparent, evanescent\ncharacter, just as the fainter shades of double\nshadows must always appear as half-shadows.\nThese latter assume colours easily, and produce\nthem readily (69), the former also (80) ; and the\nsame takes place in the instance of accessory\nimages, which, it is true, do not altogether quit\nthe real object, but still advance or extend from\nit as half-substantial images, and hence can ap-\npear coloured so quickly and so powerfully.\n\nThat the prismatic appearance is in fact an\n\n.BXPLANATION OF THE FOREGOING PHENOMENA. 97\n\naccessory image we may convince ourselves in\nmore than one mode. It corresponds exactly\nwith the form of the object itself Whether the\nobject be bounded by a straight line or a curve,\nindented or waving, the form of the accessory\nimage corresponds throughout exactly with the\nform of the object*\n\nAgain, not only the form but other qualities\nof the object are communicated to the accessory\nimage. If the object is sharply relieved from\nits ground, like white on black, the coloured\naccessory image in like manner appears in its\ngreatest force. It is vivid, distinct, and power-\nful ; but it is most especially powerful when a\nluminous object is shown on a dark ground,\nwhich may be contrived in various ways.\n\nBut if the object is but faintly distinguished\nfrom the ground, like grey objects on black or\nwhite, or even on each other, the accessory\nimage is also faint, and, when the original differ-\nence of tint or force is slight, becomes hardly\ndiscernible.\n\n* The forms in fig. 2, plate 1, when seen through a prism, are\nagain intended to exemplify this. In the plates to the original\nwork curvilinear figures are added, but the circles, fig. 1, in the\nsame plate, may answer the same end. — T.\n\n^ta=c\n\n98 EXPLANATION OF THE FOREGOING PHENOMENA.\n\nThe appearances which are observable when\ncoloured objects are relieved on light, dark, or\ncoloured grounds are, moreover, well worthy of\nattention. In this case a union takes place\nbetween the apparent colour of the accessory\nimage and the real colour of the object ; a com-\npound colour is the result, which is either assisted\nand enhanced by the accordance, or neutralised\nby the opposition of its ingredients.\n\nBut the common and general characteristic\nboth of the double and accessory image is semi-\ntransparence. The tendency of a transparent\nmedium to become only half transparent, or\nmerely light- transmitting, has been before ad-\nverted to (147, 148). Let the reader assume\nthat he sees within or through such a medium\na visionary image, and he will at once pro-\nnounce this latter to be a semi-transparent image.\n\nThus the colours produced by refraction may\nbe fitly explained by the doctrine of the semi-\ntransparent mediums. For where dark passes\nover light, as the border of the semi-transparent\naccessory image advances, yellow appears ; and,\non the other hand, where a light outline passes\nover the dark background, blue appears (150,\n151).\n\nEXPLANATION OF THE FOREGOING PHENOMENA. ,99\n\nThe advancing foremost colour is always the\nbroader. Thus the yellow spreads over the light\nwith a broad border, but the yellow-red appears\nas a narrower stripe and is next the dark, ac-\ncording to the doctrine of augmentation, as an\neffect of shade.*\n\nOn the opposite side the condensed blue is\nnext the edge, while the advancing border,\nspreading as a thinner veil over the black, pro-\nduces the violet colour, precisely on the princi-\nples before explained in treating of semi-trans-\nparent mediums, principles which will hereafter\nbe found equally efficient in many other cases.\n\nSince an analysis like the present requires to\nbe confirmed by ocular demonstration, we beg\nevery reader to make himself acquainted with\nthe experiments hitherto adduced, not in a\nsuperficial manner, but fairly and thoroughly.\nWe have not placed arbitrary signs before him\ninstead of the appearances themselves; no\nmodes of expression are here proposed for his\n\n♦ The author has before observed that colour is a degree of\ndarkness, and he here means that increase of darkness, produced by\ntransparent mediums, is, to a certain extewl, itvcxeTva^ ol tvivcwvt . — ^ .\n\n100 EXPLANATION OF THE FOREGOING PHENOMENA.\n\nadoption which may be repeated for ever with-\nout the exercise of thought and without leading\nany one to think ; but we invite him to examine\nintelligible appearances, which must be present\nto the eye and mind, in order to enable him\nclearly to trace these appearances to their ori-\ngin, and to explain them to himself and to\nothers.\n\nXVI.\n\nDECREASE OF THE APPEARANCE OF COLOUR.\n\nWe need only take the five conditions (210)\nunder which the appearance of colour increases\nin the contrary order, to produce the contrary or\ndecreasing state ; it may be as well, however,\nbriefly to describe and review the corresponding\nmodifications which are presented to the eye.\n\nAt the highest point of complete junction of\nthe opposite edges, the colours appear as fol-\nlows (216) :—\n\nYellow-red. Blue.\n\nGreen. Red.\n\nBlue-red. Yellow.\n\nDECBEASE OF THE APPEARANCE OF COLOUR. 101\n\nWhere the junction is less complete, the ap-\npearance is as follows (214, 215) : —\n\nYellow-red. Blue.\n\nYellow, Blue-red.\n\nGreen. Red.\n\nBlue. Yellow-red.\n\nBlue-red. Yellow.\n\nHere, therefore, the surface still appears\ncompletely coloured, but neither series is to be\nconsidered as an elementary series, always de-\nveloping itself in the same manner and in the\nsame degrees; on the contrary, they can and\nshould be resolved into their elements ; and, in\ndoing this, we become better acquainted with\ntheir nature and character.\n\nThese elements then are (199, 200, 201)—\n\nYellow-red.\n\nBlue.\n\nYellow.\n\nBlue-red.\n\nWhite.\n\nBlack.\n\nBlue.\n\nYellow-red.\n\nBlue-red.\n\nYellow.\n\nHere the surface itself, the original object,\nwhich has been hitherto completely covered,\nand as it were lost, again appears in the centre\nof the colours, asserts its right, ^ud ew^\\^^ \\y%\n\n-■-^^^ii unLmwahT.\n\nOmO.\n\n102 DECREASE OF THE APPEARANCE OF COLOUR.\n\nfully to recognise the secondary nature of the\naccessory images which exhibit themselves as\n•* edges \" and \" borders.\" — Note N.\n\nWe can make these edges and borders as nar-\nrow as we please ; nay, we can still have refrac-\ntion in reserve after having done away with all\nappearance of colour at the boundary of the\nobject.\n\nHaving now sufficiently investigated the ex-\nhibition of colour in this phenomenon, we repeat\nthat we cannot admit it to be an elementary\nphenomenon. On the contrary, we have traced\nit to an antecedent and a simpler one ; we have\nderived it, in connexion with the theory of se-\ncondary images, from the primordial pheno-\nmenon of light and darkness, as affected or acted\nupon by semi-transparent mediums. Thus pre-\npared, we proceed to describe the appearances\nwhich refraction produces on grey and coloured\nobjects, and this will complete the section of\nsubjective phenomena.\n\nXVII.\n\nGREY OBJECTS DISPLACED BY REFRACTION.\n\nHitherto we have confined our attention to\nblack and white objects relieved on respectively\nopposite grounds, as seen through the prism/\nbecause the coloured edges and borders are most\nclearly displayed in such cases. We now re-\npeat these experiments with grey objects, and\nagain find similar results.\n\nAs we called black the equivalent of dark-\nness, and white the representative of light (18),\nso we now venture to say that grey represents\nhalf-shadow, which partakes more or less of\nlight and darkness, and thus stands between\nthe two. We invite the reader to call to mind\nthe following facts as bearing on our present\nview.\n\nGrey objects appear lighter on a black than\non a white ground (33) ; they appear as a light\non a black ground, and larger; as a dark on the\nwhite ground, and smaller. (16.)\n\n104 GREY OBJECTS DISPLACED BY REFRACTION.\n\nThe darker the grey the more it appears as\na faint light on black, as a strong dark on white,\nand vice versd ; hence the accessory images of\ndark-grey on black are faint, on white strong :\nso the accessory images of light-grey on white\nare faint, on black strong.\n\nGrey on black, seen through the prism^ will\nexhibit the same appearances as white on black ;\nthe edges are coloured according to the same\nlaw, only the borders appear fainter. If we\nrelieve grey on white, we have the same edges\nand borders which would be produced if we saw\nblack on white through the prism. — Note O.\n\nVarious shades of grey placed next each\nother in gradation will exhibit at their edges,\neither blue and violet only, or red and yellow\nonly, according as the darker grey is placed\nover or under.\n\nA series of such shades of grey placed hori-\nzontally next each other will be coloured con-\nformably to the same law according as the whole\nseries is relieved, on a black or white ground\nabove or below.\n\nGRET OBJECTS DISPLACED BY REFRACTION. 105\n\nThe observer may see the phenomena ex-\nhibited by the prism at one glance, by enlarging\nthe plate intended to illustrate this section.*\n\nIt is of great importance duly to examine and\nconsider another experiment in which a grey\nobject is placed partly on a black and partly on\na white surface, so that the line of division\npasses vertically through the object.\n\nThe colours will appear on this grey object\nin conformity with the usual law, but according\nto the opposite relation of the light to the dark,\nand will be contrasted in a line. For as the\ngrey is as a light to the black, so it exhibits the\nred and yellow above the blue and violet below :\nagain, as the grey is as a dark to the white, the\nblue and violet appear above the red and yellow\nbelow. This experiment will be found of great\nimportance with reference to the next chapter.\n\n^ It has been thought unnecessary to give all the examples in\nthe plate alluded to, but the leading instance referred to in the\nnext paragraph will be found in plate 3, fig. 1. The grey square\nwhen seen through a prism will exhibit the effects described in\npar. 257.— T.\n\nXVIII.\n\nCOLOURED OBJECTS DISPLACED BY REFRACTION.\n\nAn unlimited coloured surface exhibits.\n* no prismatic colour in addition to its own hue,\nthus not at all differing from a black, white, or\ngrey surface. To produce the appearance of\ncolour, light and dark boundaries must act on it\neither accidentally or by contrivance. Hence\nexperiments and observations on coloured sur-\nfaces, as seen through the prism, can only be\nmade when such surfaces are separated by an\noutline from another differently tinted surface,\nin short when circumscribed objects are coloured,\n\nAll colours, whatever they may be, correspond\nso far with grey, that they appear darker than\nwhite and lighter than black. This shade-like\nquality of colour {trxispov) has been already al-\nluded to (69), and will become more and more\nevident. If then we begin by placing coloured\nobjects on black and white surfaces, and ex-\namine them through the prism, we shall again\nhave all that we have seen exhibited with grey\nsurfaces.\n\nr^- — — .v,^\n\n, — p ■ -r '\n\nCOLOURBD OBJECTS DISPLACED BY REFRACTION. 107\n\nIf we displace a coloured object by refraction,\nthere appears, as in the case of colourless ob-\njects and according to the same laws, an acces-\nsory image. This accessory image retains, as\nfar as colour is concerned, its usual nature, and\nacts on one side as a blue and blue-red, on the\nopposite side as a yellow and yellow-red. Hence\nthe apparent colour of the edge and border will\nbe either homogeneous with the real colour of\nthe object, or not so. In the first case the ap-\nparent image identifies itself with the real one,\nand appears to increase it, while, in the second\ncase, the real image may be vitiated, rendered\nindistinct, and reduced in size by the apparent\nimage. We proceed to review the cases in\nwhich these efiects are most strikingly exhibited.\n\nIf we take a coloured drawing enlarged from\nthe plate, which illustrates this experiment,*\nand examine the red and blue squares placed\nnext each other on a black ground, through the\nprism as usual, we shall find that as both colours\nare lighter than the ground, similarly coloured\nedges and borders will appear above and below,\n\n* Plate 3, fig. 1. Tho author always recommends making the\nexperiments on an increased scale, in order to sec the ])rismatic\neffects distinctly.\n\n108 COLOURED OBJECTS DISPLACED BY REFRACTION.\n\nat the outlines of both, only they will not appear\nequally distinct to the eye.\n\nRed is proportionally much lighter on black\nthan blue is. The colours of the edges will\ntherefore appear stronger on the red than on\nthe blue, which here acts as a dark-grey, but\nlittle different from black.^(251.)\n\nThe extreme red edge will identify itself with\nthe vermilion colour of the square, which will\nthus appear a little elongated in this direction ;\nwhile the yellow border immediately underneath\nit only gives the red surface a more brilliant\nappearance, and is not distinguished without\nattentive observation.\n\nOn the other hand the red edge and yellow\nborder are heterogeneous with the blue square ;\na dull red appears at the edge, and a dull green\nmingles with the figure, and thus the blue\nsquare seems, at a hasty glance, to be com-\nparatively diminished on this side.\n\nAt the lower outline of the two squares a blue\nedge and a violet border will appear, and will\n\nCOLOUBED OBJECTS DISPLACED BY REFRACTION. 109\n\nproduce the contrary effect ; for the blue edge,\nwhich is heterogeneous with the warm red sur-\nface, will vitiate it and produce a neutral colour,\nso that the red on this side appears compara-\ntively reduced and driven upwards, and the\nviolet border on the black is scarcely percep-\ntible.\n\nOn the other hand, the blue apparent edge\nwill identify itself with the blue square, and\nnot only not reduce, but extend it. The blue\nedge and even the violet border next it have\nthe apparent effect of increasing the surface,\nand elongating it in that direction.\n\nThe effect of homogeneous and heterogeneous\nedges, as I have now minutely described it, is\nso powerful and singular that the two squares\nat the first glance seem pushed out of their re-\nlative horizontal position and moved in opposite\ndirections, the red upwards, the blue down-\nwards. But no one who is accustomed to ob-\nserve experiments in a certain succession, and\nrespectively to connect and trace them, will\nsuffer himself to be deceived by such an unreal\neffect.\n\nA just impression with regard to this im^ovV\n\n■r.giJ^ifc\n\n1 10 COLOURED OBJECTS DISPLACED BY REFRACTION.\n\nant phenomenon will, however, much depend\non some nice and even troublesome conditions,\nwhich are necessary to produce the illusion in\nquestion. Paper should be tinged with vermi-\nlion or the best minium for the red square, and\nwith deep indigo for the blue square. The blue\nand red prismatic edges will then unite imper-\nceptibly with the real surfaces where they are\nrespectively homogeneous ; where they are not,\nthey vitiate the colours of the squares without\nproducing a very distinct middle tint. The real\nred should not incline too much to yellow, other-\nwise the apparent deep red edge above will be\ntoo distinct; at the same time it should be\nsomewhat yellow, otherwise the transition to the\nyellow border will be too observable. The blue\nmust not be light, otherwise the red edge will\nbe visible, and the yellow border will produce\na too decided green, while the violet border\nunderneath would not give us the impression of\nbeing part of an elongated light blue square.\n\nAll this will be treated more circumstantially\nhereafter, when we speak of the apparatus in-\ntended to facilitate the experiments connected\nwith this part of our subject.* Every inquirer\n\n* Neither the description of the apparatus nor the recapitula-\ntion of tlie whole theory, so often alluded to by the author, were\never given. — ^T.\n\nCOLOURED OBJECTS DISPLACED BY REFRACTION. Ill\n\nshould prepare the figures himself^ in order\nfairly to exhibit this specimen of ocular decep-\ntion, and at the same time to convince himself\nthat the coloured edges, even in this case, can-\nnot escape accurate examination.\n\nMeanwhile various other combinations, as\nexhibited in the plate, are fully calculated to\nremove all doubt on this point in the mind pf\nevery attentive observer.\n\nIf, for instance, we look at a white square,\nnext the blue one, on a black ground, the pris-\nmatic hues of the opposite edges of the white,\nwhich here occupies the place of the red in the\nformer experiment, will exhibit themselves in\ntheir utmost force. The red edge extends itself\nabove the level of the blue almost in a greater\ndegree than was the case with the red square\nitself in the former experiment. The lower blue\nedge, again, is visible in its full force next the\nwhite, while, on the other hand, it cannot be\ndistinguished next the blue square. 1 he violet\nborder underneath is also much more apparent\non the white than on the blue.\n\nIf the observer now compares these double\n\n-^ ~r~^^\n\n112 COLOURED OBJECTS DISPLACED BY REFRACTION.\n\nsquares, carefully prepared and arranged one\nabove the other, the red with the white, the two\nblue squares together, the blue with the red, the\nblue with the white, he will clearly perceive the\nrelations of these surfaces to their coloured\nedges and borders.\n\nThe edges and their relations to the coloured\nsurfaces appear still more striking if we look at\nthe coloured squares and a black square on a\nwhite ground ; for in this case the illusion be-\nfore mentioned ceases altogether, and the effect\nof the edges is as visible as in any case that has\ncome under our observation. Let the blue and\nred squares be first examined through the prism.\nIn both the blue edge now appears above ; this\nedge, homogeneous with the blue surface, unites\nwith it, and appears to extend it upwards, only\nthe blue edge, owing to its lightness, is some-\nwhat too distinct in its upper portion ; the vio-\nlet border underneath it is also sufficiently evi-\ndent on the blue. The apparent blue edge is,\non the other hand, heterogeneous with the red\nsquare; it is neutralised by contrast, and is\nscarcely visible; meanwhile the violet border,\nuniting with the real red, produces a hue re-\nsembling that of the peach-blossom.\n\nIf thus, owing to the above causes, the upper\n\nCOLOURED OBJECTS DISPLACED BY REFRACTION. 113\n\noutlines of these squares do not appear level\nwith each other, the correspondence of the\nunder outlines is the more observable ; for since\nboth colours, the red and the blue, are darks\ncompared with the white (as in the former case\nthey were light compared with the black), the\nred edge with its yellow border appears very\ndistinctly under both. It exhibits itself under\nthe warm red surface in its full force, and\nunder the dark blue nearly as it appears under\nthe black : as may be seen if we compare the\nedges and borders of the figures placed one\nabove the other on the white ground.\n\nIn order to present these experiments with\nthe greatest variety and perspicuity, squares\nof various colours are so arranged* that\nthe boundary of the black and white passes\nthrough them vertically. According to the\nlaws now known to us, especially in their appli-\ncation to coloured objects, we shall find the\nsquares as usual doubly coloured at each edge ;\neach square will appear to be split in two, and\nto be elongated upwards or downwards. We\nmay here call to mind the experiment with the\ngrey figure seen in like manner on the line of\ndivision between black and white (257). f\n\n* Plate iii. fig. 1 .\n\nt The grey square is introduced in the same plate, fig. 1, above\nthe coloured squares.\n\n114 COLOURED OBJECTS DISPLACED BT REFRACTION.\n\nA phenomenon was before exhibited, even to\nillusion, in the instance of a red and blue\nsquare on a black ground ; in the present expe*\nriment the elongation upwards and downwards\nof two differently coloured figures is apparent\nin the two halves of one and the same figure of\none and the same colour. Thus we are still re-\nferred to the coloured edges and borders, and to\nthe effects of their homogeneous and heteroge*\nneous relations with respect to the real colours\nof the objects.\n\nI leave it to observers themselves to compare\nthe various gradations of coloured squares,\nplaced half on black half on white, only in-\nviting their attention to the apparent alteration\nwhich takes place in contrary directions ; for\nred and yellow appear elongated upwards if on\na black ground, downwards if on a white ; blue,\ndownwards if on a black ground, upwards if on a\nwhite. All which, however, is quite in accordance\nwith the diffusely detailed examples above given.\n\nLet the observer now turn the figures so that\nthe before-mentioned squares placed on the line\nof division between black and white may be in\na horizontal series ; the black above, the white\nunderneath. On looking at these squares\n\nCOLOURED OBJTBCTB DISPLACED BT REFBACTION. 115\n\nthrough the prism, he will observe that the red\nsquare gaina by the addition of two red edges ;\non more accurate examination he will observe\nthe yellow border on the red figure, and the\nlower yellow border upon the white will be per-\nfectly apparent.\n\nThe upper red edge on the blue square is\non the other hand hardly visible ; the yellow\nborder next it produces a dull green by mingling\nwith the figure; the lower red edge and the\nyellow border are displayed in lively colours.\n\nAfter observing that the red figure in these\ncases appears to gain by an addition on both\nsides, while the dark blue, on one side at least,\nloses something; we shall see the contrary\neffect produced by turning the same figures up-\nside down, so that the white ground be above,\nthe black below.\n\nFor as the homogeneous edges and borders\nnow appear above and below the blue square,\nthis appears elongated, and a portion of the\nsurface itself seems even more brilliantly co-\nloured : it is only by attentive observation that\nwe can distinguish the edges and borders firom\nthe colour of the figure itself.\n\n116 COLOURED OBJECTS Dl8l»LACED BY REFKACTION.\n\nThe yellow and red squares, on the other\nhandy are comparatively reduced by the hetero-\ngeneous edges in this position of the figures,\nand their colours are, to a certain extent, vitiated.\nThe blue edge in both is almost invisible. The\nviolet border appears as a beautiful peach-\nblossom hue on the red, as a very pale colour of\nthe same kind on the yellow ; both the lower\nedges are green ; dull on the red, vivid on the\nyellow ; the violet border is but faintly percep-\ntible under the red, but is more apparent under\nthe yellow.\n\nEvery inquirer should make it a point to be\nthoroughly acquainted with all the appearances\nhere adduced, and not consider it irksome to\nfollow out a single phenomenon through so\nmany modifying circumstances. These expe-\nriments, it is true, may be multiplied to infinity\nby differently coloured figures, upon and be-\ntween differently coloured grounds. Under all\nsuch circumstances, however, it will be evident\nto every attentive observer that coloured squares\nonly appear relatively altered, or elongated, or\nreduced by the prism, because an addition of\nhomogeneous or heterogeneous edges produces\nan illusion. .The inquirer will now be enabled\nto do away with this illusion if he has the\n\nCOLOURED OBJECTS DISPLACED BY REFRACTION. 117\n\npatience to go through the experiments one after\nthe other, always comparing the effects together,\nand satisfying himself of their correspondence.\n\nExperiments with coloured objects might\nhave been contrived in various ways : why they\nhave been exhibited precisely in the above mode,\nand with so much minuteness, will be seen here-*\nafter. The phenomena, although formerly not\nunknown, were much misunderstood ; and it was\nnecessary to investigate them thoroughly to\nrender some portions of our intended historical\nview clearer.\n\nIn conclusion, we will mention a contrivance\nby means of which our scientific readers may be\nenabled to see these appearances distinctly at\none view, and even in their greatest splendour.\nCut in a piece of pasteboard five perfectly simi-»\nlar square openings of about an inch, next each\nother, exactly in a horizontal line : behind these\nopenings place five coloured glasses in the na«\ntural order, orange, yellow, green, blue, violet.\nLet the series thus adjusted be fastened in an\nopening of the camera obscura, so that the\nbright sky may be seen through the squares,\nor that the sun may shine on them ; they\nwill thus appear very powerfully coloured. Let\nthe spectator now examine them through the\nprism, and observe the appearances, already\n\n1 IB ACHBOMATISM AND HTPERCHBOMATISM.\n\nfiBudiliar by the foregoing experimentSi with\ncoloured objects, namely > the partly assisting^\npartly neutralising effects of the edges and born\ndersy and the consequent apparent elongation or\nreduction of the coloured squares with reference\nto the horizontal line. The results witnessed by\nthe observer in this case, entirely correspond\nwith those in the cases before analysed ; we do\nnot, therefore, go through them again in detail,\nespecially as we shall find frequent occasions\nhereafter to return to the subject. — Note P.\n\nACHBOMATISM AND HTFEBCHROMATISM.\n\nFormerly when much that is regular and con-\nstant in nature was considered as mere aber^\nration and accident, the colours arising from re-\nfraction were but little attended to, and were\nlooked upon as an appearance attributable to\nparticular local circumstances.\n\nBut after it had been assumed that this ap-\npearance of colour accompanies refraction at all\ntimes, it was natural that it should be considered\nas intimately and exclusively connected with\nthat phenomenon ; the belief obtaining that the\n\nACBEOMATISM AND HTPEBCUKOMATISM. 119\n\nmiea9ure of the coloured appearance was in pro-\nportion to the measure of the refraction, and\nthat they must advance pari passu with each\nother.\n\nIf, again^ philosophers ascribed the pheno-\nmenon of a stronger or weaker refraction, not\nindeed wholly, but in some degree, to the dif-\nferent density of the medium^ (as purer atmo-\nspheric air, air charged with vapours, water,\nglass^ according to their increasing density, in-\ncrease the so-called refraction, or displacement\nof the object;) so they could hardly doubt that\nthe appearance of colour must increase in the\nsame proportion ; and hence took it for granted,\nin combining different mediums which were to\ncounteract refraction, that as long as refraction\nexisted, the appearance of colour must take\nplace, and that as soon as the colour disappeared,\nthe refraction also must cease.\n\nAfterwards it was, however, discovered that\nthis relation which was assumed to correspond,\nwas, in fact, dissimilar ; that two mediums can\nrefract an object with equal power, and yet pro-\nduce very dissimilar coloured borders.\n\nIt was found that, in addition to the physical\nprinciple to which refraction was ascribed, a\n\n120 ACHROMATISM AND HTFEBCHBOMATIStf.\n\nchemical one was also to be taken into the\naccount. We propose to pursue this subject\nhereafter, in the chemical division of our in*\nquiry, and we shall have to describe the par-\nticulars of this important discovery in our history\nof the doctrine of colours. What follows may\nsuffice for the present.\n\nIn mediums of similar or nearly similar re-\nfracting power, we find the remarkable circum-\nstance that a greater and lesser appearance of\ncolour can be produced by a chemical treat-\nment ; the greater effect is owing, namely, to\nacids, the lesser to alkalis. If metallic oxydes\nare introduced into a common mass of glass, the\nColoured appearance through such glasses be-\ncomes greatly increased without any perceptible\nchange of refracting power. That the lesser\neffect, again, is produced by alkalis, may be\neasily supposed.\n\nThose kinds of glass which were first em-\nployed after the discovery, are called flint and\ncrown glass ; the first produces the stronger,\nthe second the fainter appearance of colour.\n\nWe shall make use of both these denomina-\ntions as technical terms in our. present statement.\n\nACHROMATISM AND HTFERCHROMATISM. 121\n\nand assume that the refractive power of both is\nthe same, but that flint-glass produces the\ncoloured appearance more strongly by one-third\nthan the crown-glass. The diagram (Plate 3,\nfig. 2>) may serve in illustration.\n\nA black surface is here divided into com-*\npartments for more convenient demonstration :\nlet the spectator imagine five white squares be-\ntween the parallel lines a, h, and e, d. The\nsquare No. 1 , is presented to the naked eye un-\nmoved from its place.\n\n\\ 294.\n\nBut let the square No. 2, seen through a\ncrown-glass prism g, be supposed to be dis-\nplaced by refraction three compartments, ex-\nhibiting the coloured borders to a certain extent ;\nagain, let the square No. 3, seen through a flint\nglass prism A, in like manner be moved down-\nwards three compartments, when it will exhibit\nthe coloured borders by about a third wider\nthan No. 2.\n\nAgain, let us suppose that the square No. 4,\nhas, like No. 2, been moved downwards three\ncompartments by a prism of crown-glass, and\nthat then by an oppositely placed prism A, of\n\n>**^'\n\n■±a«\n\n122 ACHROMATISM AND HTTEBCHEOMATISM.\n\nflint-glass, it has been again raised to its former\nsituation, where it now stands.\n\nHere, it is true, the refraction is done away\nwith by the opposition of the two ; but as the\nprism A, in displacing the square by refraction\nthrough three compartments, produces coloured\nborders wider by a third than those produced by\nthe prism g, so, notwithstanding the refraction\nis neutralised, there must be an excess of\ncoloured border remaining. (The position of this\ncolour, as usual, depends on the direction of the\napparent motion (204) communicated to the\nsquare by the prism h, and, consequently^ it is\nthe reverse of the appearance in the two squares\n2 and 3, which have been moved in an opposite\ndirection.) This excess of colour we have called\nHyperchromatism, and from this the achromatic\nstate may be immediately arrived at\n\nFor assuming that it was the square No. 5\nwhich was removed three compartments from\nits first supposed place, like No. 2, by a prism\nof crown-glass g, it would only be necessary to\nreduce the angle of a prism of flint-glass A, and\nto connect it, reversed, to the prism g^ in order\nto raise the square No. 5 two degrees or com<*\npartments; by which means the Hyperchro-\n\nADVANTAGES OF SUBJECTIVE EXPERIMENTS. 123\n\nmatism of the first case would cease, the figure\nwould not quite return to its first position, and\nyet be already colourless. The prolonged lines\nof the united prisms, under No. 5, show that a\nsingle complete prism remains : again, we have\nonly to suppose the lines curved, and an object-\nglass presents itself. Such is the principle of\nthe achromatic telescopes.\n\nFor these experiments, a small prism com--\nposed of three different prisms, as prepared in\nEngland, is extremely well adapted. It is to be\nhoped our own opticians will in future enable\nevery friend of science to provide himself with\nthis necessary instrument.\n\nADVANTAGES OF SUBJECTIVE EXPERIMENTS.— TRANSITION\n\nTO THE OBJECTIVE.\n\nWe have presented the appearances of colour\nas exhibited by refraction, first, by means of\nsubjective experiments; and we have so far\narrived at a definite result, that we have been\nenabled to deduce the phenomena in question\n\n] 24 ADVANTAGES OF SUBJECTIVE EXPERIMENTS-^\n\nfrom the doctrine of semi-transparent* mediums\nand double images.\n\nIn statements which have reference to nature,\neverything depends on ocular inspection^ and\nthese experiments are the more satisfactory as\nthey may be easily and conveniently made.\nEvery amateur can procure his apparatus with-\nout much trouble or cost, and if he is a tolerable\nadept in pasteboard contrivances, he may even\nprepare a great part of his machinery himself.\nA few plain surfaces, on which black, white,\ngrey, and coloured objects may be exhibited\nalternately on a light and dark ground, are all\nthat is necessary. The spectator fixes then)\nbefore him, examines the appearances at the\nedge of the figures conveniently, and as long as\nhe pleases ; he retires to a greater distance,\nagain approaches, and accurately observes the\nprogressive states of the phenomena.\n\nBesides this, the appearances may be ob-\nserved with sufficient exactness through small\nprisms, which need not be of the purest glass.\n\nThe other desirable requisites in these glass in-\nstruments will, however, be pointed out in the\nsection which treats of the apparatus.*\n\n* This description of the apparatus was never given.\n\nOBJECTIVE EXPERIMENTS. 125\n\nA great advantage in these experiments, again,\nis^ that they can be made at any hour of the day\nin any room, whatever aspect it may have. We\nhave no need to wait for sunshine, which in\ngeneral is not very propitious to northern ob-\nservers.\n\nOBJECTIVE EXPERIMENTS.\n\nThe objective experiments, on the contrary,\nnecessarily require the sun-light which, even\nwhen it is to be had, may not always have the\nmost desirable relation with the apparatus\nplaced opposite to it. Sometimes the sun is\ntoo high, sometimes too low, and withal only a\nshort time in the meridian of the best situated\nroom. It changes its direction during the ob-\nservation,' the observer is forced to alter his own\nposition and that of his apparatus, in conse-\nquence of which the experiments in many cases\nbecome uncertain. If the sun shines through\nthe prism it exhibits all inequalities, lines,\nand bubbles in the glass, and thus the appear-\nance is rendered confused, dim, and discoloured.\n\nYet both kinds of experiments must be inves-\ntigated with equal accuracy. They appear to\n\n130 OBJECTIVE EXPERIMENTS.\n\nbe opposed to each other, and yet are alwajrs\njl^ralleL What one order of experiments exhi-\nbits the other exhibits likewise, and yet each\nhas its peculiar capabilities, by means of which\ncertain effects of nature are made known to us\nin more than one way.\n\nIn the next place there are important pheno-\nmena which may be exhibited by the union of\nsubjective and objective experiments. The\nlatter experiments again have. this advantage^\nthat we can in most cases represent them by\ndiagrams, and present to view the component\nrelations of the phenomena. In proceeding^\ntherefore, to describe the objective experiments,\nwe shall so arrange them that they may always\ncorrespond with the analogous subjective exam*\npies ; for this reason, too, we annex to the num-\nber of each paragraph the number of the former\ncorresponding one. But we set out by ob-\nserving generally that the reader must consult\nthe plates, that the scientific investigator must\nbe femiliar with the apparatus in order that the\ntwin-phenomena in one mode or the other may\nbe placed before them.\n\nXXI.\n\nREFBACTION WITHOUT THE AFFEA&ANCE OF COLOUB.\n\n306 (195, 196).\n\nThat refraction may exhibit its effects without\nproducing an appearance of colour, is not to be\ndemonstrated so perfectly in objective as in sub-\njective experiments. We have, it is true, un-\nlimited spaces which we can look at through\nthe prism, and thus convince ourselves that no\ncolour appears where there is no boundary ; but\nwe have no unlimited source of light which we\ncan cause to act through the prism. Our light\ncomes to us from circumscribed bodies ; and\nthe sun, which chiefly produces our prismatic\nappearances, is itself only a small, circum-\nscribed, luminous object.\n\nWe may, however, consider every larger open-\ning through which the sun shines, every larger\nmedium through which the sun-light is trans-\nmitted and made to deviate from its course, as\nso far unlimited that we can confine our atten-\ntion to the centre of the surface without con-\nsidering its boundaries.\n\n308 (197).\nIf we place a large water-prVstu m \\Xvfe ^\\«\\n 'o^\n\n— *- -\n\n128 CONDITIONS OF THE APPEARANCE OF COLOUR.\n\nlarge bright space is refracted upwards by it on\nthe plane intended to receive the image, and the\nmiddle of this illumined space will be colourless.\nThe same effect may be produced if we make\nthe experiment with glass prisms haying angles\nof few degrees : the appearance may be pro«\nduced even through glass prisms, whose re-\nfracting angle is sixty degrees, provided we\nplace the recipient surface near enough.\n\nXXII.\n\nCONDITIONS OF THE APPEARANCE OF COLOUR.\n\n309 (198).\n\nAlthough, then, the illumined space before\nmentioned appears indeed refracted and moved\nfrom its place, but not coloured, yet on the hori-\nzontal edges of this space we observe a coloured\nappearance. That here again the colour is\nsolely owing to the displacement of a circum-\nscribed object may require to he more fully\nproved.\n\nThe luminous body which here acts is cir-\ncumscribed : the sun, while it shines and diffuses\nlight, is still an insulated object. However\nsmall the opening in the ltd of a camera obscura\nbe made, still the whole image of the sun will\n\nCONDITIONS OF THE APPEARANCE OF COLOUR. 129\n\npenetrate it. The light which streams from all\nparts of the sun's disk, will cross itself in the\nsmallest opening, and form the angle which\ncorresponds with the sun's apparent diameter.\nOn the outside we have a cone narrowing to the\norifice ; within, this apex spreads again, produc-\ning on an opposite surface a round image, which\nstill increases in size in proportion to the dis-*\ntance of the recipient surface from the apex.\nThis image, together with all other objects of\nthe external landscape, appears reversed on the\nwhite surface in question in a dark room.\n\nHow little therefore we have here to do with\nsingle sun-rays, bundles or fasces of rays, cylin-\nders of rays, pencils, or whatever else of the kind\nmay be imagined, is strikingly evident. For the\nconvenience of certain diagrams the sun-light\nmay be assumed to arrive in parallel lines, but\nit is known that this is only a fiction ; a fiction\nquite allowable where the difference between\nthe assumption and the true appearance is un-\nimportant ; but we should take care not to suffer\nsuch a postulate to be equivalent to a fact, and\nproceed to further operations on such a fictitious\nbasis.\n\nLet the aperture in the window-shutter be\nnow enlarged at pleasure, let it be mvAe \\qw\\A\n\na^\n\n130 CONDITIONS OF THB AFPEARANCB OF COLOUR.\n\nor square, nay, let the whole shatter be opened,\nand let the sun shine into the room through the\nwhole window ; the space which the sun illu-\nmines will always be larger according to the\nangle which its diameter makes ; and thus even\nthe whole space illumined by the sun through\nthe largest window is only the image of the sun\npbis the size of the opening. We shall hereafter\nhave occasion to return to this.\n\n312 (199).\n\nIf we transmit the image of the sun through\nconvex glasses we contract it towards the focus.\nIn this case, according to the laws before ex-\nplained, a yellow border and a yellow-red edge\nmust appear when the spectrum is thrown on\nwhite paper. But as this experiment is dazzling\nand inconvenient, it may be made more agree-\nably with the image of the full moon. On con-\ntracting this orb by means of a convex glass, the\ncoloured edge appears in the greatest splendor ;\nfor the moon transmits a mitigated light in the\nfirst instance, and can thus the more readily\nproduce colour which to a certain extent accom-\npanies the subduing of light : at the same time\nthe eye of the observer is only gently and agree-\nably excited.\n\n313 (200).\n\nIf we transmit a luminous image through con-\n\nCONDITIONS OF THB APPEARANCE OF COLOUR. 131\n\ncave glasses, it is dilated. Here the image ap-\npears edged with blue.\n\nThe two opposite appearances may be pro-\nduced by a convex glass, simultaneously or in\nsuccession; simultaneously by fastening an\nopaque disk in the centre of the convex glass,\nand then transmitting the sun's image. In this\ncase the luminous image and the black disk\nwithin it are both contracted, and, consequently,\nthe opposite colours must appear. Again, we\ncan present this contrast in succession by first\ncontracting the luminous image towards the\nfocus, and then suffering it to expand again\nbeyond the focus, when it will immediately ex-\nhibit a blue edge.\n\n315 (201).\n\nHere too what was observed in the subjective\nexperiments is again to be remarked, namely,\nthat blue and yellow appear in and upon the\nwhite, and that both assume a reddish appear-\nance in proportion as they mingle with the\nblack.\n\n316 (202, 203).\n\nThese elementary phenomena occur in all\nsubsequent objective experiments, as they cow-\nstituted the groundwork of tVie s\\i\\>^^e\\Iv^e wv^^\n\nfrr-ii-r\n\n132 CONDITIONB OF THE APPEARANCE OF COLOUR.\n\nThe process too which takes place is the same ;\na light boundary is carried over a dark surface,\na dark surface is carried over a light boundary.\nThe edges must advance, and as it were push\nover each other in these experiments as in the\nformer ones.\n\n317 (204).\n\nIf we admit the sun's image through a larger\nor smaller opening into the dark room, if we\ntransmit it through a prism so placed that its\nrefracting angle, as usual, is underneath; the\nluminous image, instead of proceeding in a\nstraight line to the floor, is refracted upwards\non a vertical surface placed to receive it. This\nis the moment to take notice of the opposite\nmodes in which the subjective and objective re-\nfractions of the object appear.\n\nIf we look through a prism, held with its re-\nfracting angle underneath, at an object above\nus, the object is moved downward^; whereas a\nluminous image refracted through the same\nprism is moved upwards. This, which we here\nmerely mention as a matter of fact for the sake\nof brevity, is easily explained by the laws of re-\nfraction and elevation.\n\nCONDITIONS OF THE APPEABANCE OF COLOUR* 133\n\nThe luminoulB object being moved from its\nplace in this manner, the coloured borders ap-\npear in the order, and according to the laws\nbefore explained. The violet border is always\nforemost, and thus in objective cases proceeds\nupwards, in subjective cases downwards.\n\n320 (205).\n\nThe observer may convince himself in like\nmanner of the mode in which the appearance of\ncolour takes place in the diagonal direction\nwhen the displacement is effected by means of\ntwo prisms, as has been plainly enough shown\nin the subjective example ; for this experiment,\nhowever, prisms should be procured of few de-\ngrees, say about fifteen.\n\n321 (206, 207).\n\nThat the colouring of the image takes place\nhere too, according to the direction in which it\nmoves, will be apparent if we make a square\nopening of moderate size in a shutter, and\ncause the luminous image to pass through a\nwater-prism ; the spectrum being moved first in\nthe horizontal and vertical directions, then dia-\ngonally, the coloured edges will change their\nposition accordingly.\n\n134 COKDmOKS OF THB 4FPEABANCE OF COLOUR.\n\n322 (208).\n\nWhence it is again evident that to produce\ncolour the boundaries must be carried over each\nother, not merely move side by side.\n\nXXIII.\n\ncoNDrriONs of the increase of colour.\n\n323 (209).\n\nHere too an increased displacement of the ob-\nject produces a greater appearance of colour.\n\n324 (210).\n\nThis increased displacement occurs,\n\n1. By a more oblique direction of the im-\npinging luminous object through mediums with\nparallel surfaces.\n\n2. By changing the parallel form for one\nmore or less acute angled.\n\n3. By increased proportion of the medium,\nwhether parallel or acute angled; partly be-\ncause the object is by this means more power-\nfully displaced, partly because an effect depend-\ning on the mere mass co-operates.\n\n4. By the distance of the recipient surface\nfrom the refracting medium so that the coloured\n\nCONDITIONS OF THE INCEBA8E OF COLOUR. 135\n\nspectrum emerging from the prism may be said\nto have a longer way to travel.\n\n5. When a chemical property produces its\neffects under all these circumstances: this we\nhave already entered into more fully under the\nhead of achromatism and hyperchromatism.\n\n325 (211).\n\nThe objective experiments have this advan-\ntage that the progressive states of the pheno-\nmenon may be arrested and clearly represented\nby diagrams^ which is not the case with the\nsubjective experiments.\n\nWe can observe the luminous image after it\nhas emerged from the prism, step by step, and\nmark its increasing colour by receiving it on a\nplane at different distances, thus exhibiting\nbefore our eyes various sections of this cone,\nwith an elliptical base : again, the phenomenon\nmay at once be rendered beautifully visible\nthroughout its whole course in the following\nmanner : — Let a cloud of fine white dust be ex-\ncited along the line in which the image passes\nthrough the dark space ; the cloud is best pro-\nduced by fine, perfectly dry, hair-powder. The\nmore or less coloured appearance will now be\npainted on the white atoms, ^xvdi Y^^^^w\\fe^\\\\v\n\n1 30 CONDITIONS OF THE INCREASE OF COLOUR.\n\nits whole length and breadth to the eye of the\nspectator.\n\nBy this means we have prepared some dia-\ngrams, which will be found among the plates.\nIn these the appearance is exhibited from its\nfirst origin, and by these the spectator can\nclearly comprehend why the luminous image is\nso much more powerfully coloured through\nprisms than through parallel mediums.\n\n828 (212).\n\nAt the two opposite outlines of the image an\nopposite appearance presents itself, beginning\nfrom an acute angle ;* the appearance spreads as\nit proceeds further in space, according to this\nangle. On one side, in the direction in which\nthe luminous image is moved^ a violet border\nadvances on the dark, a narrower blue edge re-\nmains next the outline of the image. On the\nopposite side a yellow border advances into the\nlight of the image itself, and a yellow-red edge\nremains at the outline.\n\n329 (213).\n\nHere, therefore, the movement of the dark\nagainst the light, of the light against the dark,\nmay be clearly observed.\n\n♦ Plate iv. fig. I.\n\nCONDITIONS OF THE INCBSA8E OF COLOUR. 137\n\n330 (214).\n\nThe centre of a large object remains long un-\ncolouredy especially with mediums of less den-\nsity and smaller angles ; but at last the oppo-\nsite borders and edges touch each other, upon\nwhich a green appears in the centre of the lu-\nminous image.\n\n331 (215).\n\nObjective experiments have been usually\nmade with the sun's image : an objective expe-\nriment with a dark object has hitherto scarcely\nbeen thought of. We have, however, prepared\na convenient contrivance for this also. Let the\nlarge water-prism before alluded to be placed in\nthe sun, and let a round pasteboard disk be\nfastened either inside or outside. The coloured\nappearance will again take place at the outline,\nbeginning according to the usual law ; the edges\nwill appear, they will spread in the same pro-\nportion, and when they meet, red will appear in\nthe centre.* An intercepting square may be\nadded near the round disk, and placed in any\ndirection ad libitum^ and the spectator can again\nconvince himself of what has been before so\noften described.\n\n332 (216).\n\nIf we take away these dark objects frovcL \\!afc\n\nPlate iv. fig. ^.\n\n^\n\n138 00KDITI0K8 OF THS XNCRSABB OP COLOUR.\n\nprism, in which case, however, the glass is to be\ncarefully cleaned, and hold a rod or a large\npencil before the centre of the horizontal prism>\nwe shall then accomplish the complete immixture\nof the violet border and the yellow-red edge,\nand see only the three colours, the external\nblue, and yellow, and the central red.\n\nIf again we cut a long horizontal opening in\nthe middle of a piece of pasteboard, fastened on\nthe prism, and then cause the sun-light to pass\nthrough it, we shall accomplish the complete\nunion of the yellow border with the blue edge\nupon the light, and only see yellow-red, green\nand violet The details of this are further\nentered into in the description of the plates.\n\n334 (217).\n\nThe prismatic appearance is thus by no\nmeans complete and final when the luminous\nimage emerges from the prism. It is then only\nthat we perceive its elements in contrast ; for as\nit increases these contrasting elements unite,\nand are at last intimately joined. The section\nof this phenomenon arrested on a plane surface\nis difierent at every degree of distance from the\nprism ; so that the notion of an immutable series\nof colours, or of a pervading similar proportion\nbetween them, cannot be a question for a\nmoment.\n\nEXPLANATION OF THE FOBBQOINO PHENOBIBNA. 139\n\nXXIV.\n\nEXPLANATION OF THE FOREGOING PHENOMENA.\n\n335 (218).\n\nAs we have already entered into this analysis\ncircumstantially while treating of the subjective\nexperiments, as all that was of force there is\nequally valid here, it will require no long de-\ntails in addition to show that the phenomena^\nwhich are entirely parallel in the two cases, may\nalso be traced precisely to the same sources.\n\n336 (219).\n\nThat in objective experiments also we have\nto do with circumscribed images, has been al-\nready demonstrated at large. The sun may\nshine through the smallest opening, yet the\nimage of the whole disk penetrates beyond.\nThe largest prism may be placed in the open\nsun-light, yet it is still the sun's image that is\nbounded by the edges of the refracting surfaces,\nand produces the accessory images of this bound-\nary. We may fasten pasteboard, with many\nopenings cut in it, before the water-prism, yet\nwe still merely see multiplied images which,\nafter having been moved from their place by\nrefraction, exhibit coloured edges and borders,\nand in these mere accessory \\mv)L%e:8»«\n\n140 EXPLANATION OF THE FOREQOINO PHENOMENA.\n\n337 (235),\n\nIn subjective experiments we have seen that\nobjects strongly relieved from each other pro-\nduce a very lively appearance of colour, and\nthis will be the case in objective experiments in\na much more vivid and splendid degree. The\nsun's image is the most powerful brightness we\nknow ; hence its accessory image will be ener-\ngetic in proportion, and notwithstanding its\nreally secondary dimmed and darkened charac-\nter, must be still very brilliant. The colours\nthrown by the sun-light through the prism on\nany object, carry a powerful light with them,\nfor they have the highest and most intense\nsource of light, as it were, for their ground.\n\nThat we are warranted in calling even these\naccessory images semi-transparent, thus de*\nducing the appearances from the doctrine of\nthe semi-transparent mediums, will be clear to\nevery one who has followed us thus far, but par-\nticularly to those who have supplied themselves\nwith the necessary apparatus, so as to be en-\nabled at all times to witness the precision and\nvivacity with which semi-transparent mediums\nact.\n\nDECREASE OF THE APPEARANCE OF COLOUR. 141\n\nXXV.\n\nDECREASE OF THE APPEARANCE OF COLOUR.\n\n339 (243).\nIf we could afford to be concise in the descrip-\ntion of the decreasing coloured appearance in\nsubjective cases, we may here be permitted to\nproceed with still greater brevity while we refer\nto the former distinct statement. One circum-\nstance, only on account of its great importance,\nmay be here recommended to the reader's espe-\ncial attention as a leading point of our whole\nthesis.\n\n340 (244, 247).\nThe decline of the prismatic appearance\nmust be preceded by its separation, by its reso-\nlution into its elements. At a due distance from\nthe prism, the image of the sun being entirely\ncoloured, the blue and yellow at length mix\ncompletely, and we see only yellow-red, green,\nand blue-red. If we bring the recipient surface\nnearer to the refracting medium, yellow and\nblue appear again, and we see the five colours\nwith their gradations. At a still shorter dis-\ntance the yellow and blue separate from each\nother entirely, the green vanishes, and the\nimage itself appears, colourless, between the\ncoloured edges and borders. The nearer we\nbring the recipient surface lo \\\\ve ys:\\^\\s\\> ^^\n\n»<i:.-.\n\n142 OBEY OBJECTS.\n\nnarrower the edges and borders become, till at\nlast, when in contact with the prism, they are\nreduced to nothing.\n\nOBEY OBJECTS.\n\n341 (218).\n\nWe have exhibited grey objects as very im-\nportant to our inquiry in the subjective experi-\nments. They show, by the faintness of the\naccessory images, that these same images are in\nall cases derived from the principal object. If\nwe wish here, too, to carry on the objective ex-\nperiments parallel with the others, we may con-\nveniently do this by placing a more or less dull\nground glass before the opening through which\nthe sun's image enters. By this means a sub-\ndued image would be produced, which on being\nrefracted would exhibit much duller colours on\nthe recipient plane than those immediately de-\nrived from the sun's disk ; and thus, even fi*om\nthe intense sun-image, only a faint accessory\nimage would appear, proportioned to the mi-\ntigation of the light by the glass. This expe-\nriment, it is true^ will only again and again\nconfirm what is already sufficiently familiar\n\nto U8.\n\nCOLOUBXD 0BJSCT8. 143\n\nXXVII.\n\nCOLOURBD OBJECTS.\n\n342 (260).\nThere are various modes of producing coloured\nimages in objective experiments. In the first\nplace, we can fix coloured glass before the open-\nings by which means a coloured image is at once\nproduced ; secondly, we can fill the water-prism\nwith coloured fluids ; thirdly, we can cause the\ncolours, already produced in their full vivacity\nby the prism, to pass through proportionate\nsmall openings in a tin plate, and thus prepare\nsmall circumscribed colours for a second opera-\ntion. This last mode is the most difficult ; for\nowing to the continual progress of the sun, the\nimage cannot be arrested in any direction at\nwill. The second method has also its incon-\nveniences, since not all coloured liquids can\nbe prepared perfectly bright and clear. On\nthese accounts the first is to be preferred, and\ndeserves the more to be adopted because natural\nphilosophers have hitherto chosen to consider\nthe colours produced from the sun-light through\nthe prism, those produced through liquids and\nglasses, and those which are already fixed on\npaper or cloth, as exhibiting effects equally to\nbe depended on, and equally available in de-\nmonstration.\n\nAs it 18 thus merely necessary \\X\\a\\.\\)tvfc\"va^a3^\n\n144 COLOUSBD OBJECTS/\n\nshould be coloured^* 00 the large water-prism\nbefore alluded to affords us th^ best means of\neffecting this. A pasteboard screen may be\ncontrived to slide before the large surfaces of\nthe prism, through which^ in the first instance,\nthe light passes uncoloured. In this screen\nopenings of various forms may be cut, in order\nto produce different images, and consequently\ndifferent accessory images. This being done,\nwe need only fix coloured glasses before the\nopenings, in order to observe what effect refrac-\ntion produces on coloured images in an objective\nsense.\n\nA series of glasses may be prepared in a\nmode similar to that before described (284) ;\nthese should be accurately contrived to slide in\nthe grooves of the large water-prism. Let the\nsun then shine through them, and the coloured\nimages refracted upwards will appear bordered\nand edged, and will vary accordingly: for\nthese borders and edges will be exhibited quite\ndistinctly on some images, and on others will\nbe mixed with the specific colour of the glass,\nwhich they will either enhance or neutralize.\nEvery observer will be enabled to convince\nhimself here again that we have only to do with\nthe same simple phenomenon so circumstan-\niially described subjectively and objectively.\n\nACHROMATISM AND HTPERCHROMATISM. 145\n\nXXVIII.\n\nACHROMATISM AND HTPERCHROMATISM.\n\n345 (285, 290).\n\nIt is possible to make the hyperchromatic and\nachromatic experiments objectively as well as\nsubjectively. After what has been already\nstated, a short description of the method will\nsuffice, especially as we take it for granted that\nthe compound prism before mentioned is in the\nhands of the observer.\n\nLet the sun's image pass through an acute-\nangled prism of few degrees, prepared from\ncrown-glass, so that the spectrum be refracted\nupwards on an opposite surface ; the edges will\nappear coloured, according to the constant law,\nnamely, the violet and blue above and outside,\nthe yellow and yellow-red below and within the\nimage. As the refracting angle of this prism is\nundermost^ let another proportionate prism of\nflint-glass be placed against it, with its refracting\nangle uppermost. The sun's image will by this\nmeans be again moved to its place, where, owing\nto the excess of the colouring power of the\nprism of flint-glass, it will still appear a little\ncoloured, and, in consequence of the direction\nin which it has been moved, the blvxa ^\\A n\\s\\^\\.\n\n146 ACHROMATISM AND HTBERCHROMATISM.\n\nwill now appear underneath and outside, the\nyellow and yellow-red above and inside.\n\nIf the whole image be now moved a little up-\nwards by a proportionate prism of crown-glass,\nthe hyperchromatism will disappear, the sun's\nimage will be moved from its place, and yet\nwill appear colourless.\n\nWith an achromatic object-glass composed of\nthree glasses, this experiment may be made\nstep by step, if we do not mind taking out the\nglasses from their setting. The two convex\nglasses of crown-glass in contracting the sun's\nimage towards the focus, the concave glass of\nflint-glass in dilating the image beyond it, ex-\nhibit at the edges the usual colours. A convex\nglass united with a concave one, exhibits the\ncolours according to the law of the latter. If\nall three glasses are placed together, whether\nwe contract the sun's image towards the focus,\nor suffer it to dilate beyond the focus, coloured\nedges never appear, and the achromatic effect\nintended by the optician is, in this case, again\nattained.\n\nBut as the crown-glass has always a greenish\ntint, and as a tendency to this hue may be more\n\nACHROMATISM AND HTPERCHBOMATISM. 147\n\nin large and strong object-glasses,\nand under certain circumstances produce the\ncompensatory red> (which, however, in repeated\nexperiments with several instruments of this\nkind did not occur to us,) philosophers have\nresorted to the most extraordinary modes of\nexplaining such a result ; and having been com-\npelled, in support of their system, theoretically\nto prove the impossibility of achromatic tele-\nscopes, have felt a kind of satisfoction in having\nsome apparent ground for denying so great an\nimprovement. Of this, however, we can only\ntreat circumstantiaUy in our historical account\nof these discoveries.\n\nXXIX.\n\nCOMBINATION OF SUBJECTIVE AND OBJECTIVE\n\nEXPERIMENTS.\n\nHaving shown above (318) that refraction, con-\nsidered objectively and subjectively, must act in\nopposite directions, it will follow that if we com-\nbine the experiments, the effects will recipro-\ncally destroy each other.\n\nLet the sun's image be Ihto^w uy^^^^\"^ ^\"^ '^\n\n148 COMBINATION OF SUBJECTIVE\n\nvertical plane, through a horizontally-placed\nprism. If the prism is long enough to admit of\nthe spectator also looking through it, he will see\nthe image* elevated by the objective refraction\nagain depressed, and in the same place in which\nit appeared without refraction.\n\nHere a remarkable case presents itself, but\nat the same time a natural result of a general\nlaw. For since, as often before stated, the ob-\njective sun's image thrown on the vertical\nplane is not an ultimate or unchangeable state\nof the phenomenon, so in th^ above operation\nthe image is not only depressed when seen\nthrough the prism, but its edges and borders\nare entirely robbed of their hues, and the\nspectrum is reduced to a colourless circular\nform.\n\nBy employing two perfectly similar prisms\nplaced next each other, for this experiment, we\ncan transmit the sun's image through one, and\nlook through the other.\n\nIf the spectator advances nearer with the\n\nprism through which he looks, the image is\n\nagain elevated, and by degrees becomes coloured\n\naccording to the law of the first prism. If he\n\nAND OBJECTIVE EXPERIMENTS. 149\n\nagain retires till he has brought the image to the\nneutralized point, and then retires still farther\naway, the image, which had become round and\ncolourless, moves still more downwards and be-\ncomes coloured in the opposite sense, so that if\nwe look through the prism and upon the re-\nfracted spectrum at the same time, we see the\nsame image coloured according to subjective and\nobjective laws.\n\nThe modes in which this experiment may be\nvaried are obvious. If the refracting angle of\nthe prism, through which the sun's image was\nobjectively elevated, is greater than that of the\nprism through which the observer looks, he\nmust retire to a much greater distance, in order\nto depress the coloured image so low on the\nvertical plane that it shall appear colourless,\nand vice versd.\n\nIt will be easily seen that we may exhibit\nachromatic and hyperchromatic effects in a\nsimilar manner, and we leave it to the amateur\nto follow out such researches more fully. Other\ncomplicated experiments in which prisms and\nlenses are employed together, others again, in\nwhich objective and subjective experiments are\nvariously intermixed, we te«>etN^ i^\\ ^ S»Nxa^^\n\n150 TBAN8ITI0N.\n\noccasion, when it will be our object to trace such\neffects to the simple pheoomeDa with which we\nare now sufficiently familiar.\n\nXXX.\n\nTRANSITION.\n\nIn looking back on the description and analysis\nof dioptrical colours, we do not repent either\nthat we have treated them ao circumstantially,\nor that we have taken them into consideration\nbefore the other physical colours, out of the\norder we ourselves laid down. Yet, before we\nquit this branch of our inquiry, it may be as\nwell to state the reasons that have weighed\nwith us.\n\nIf some apol<^ is necessary for having\ntreated the theory of the dioptrical colours, par-\nticularly those of the second class, so diffusely,\nwe should observe, that the exposition of any\nbranch of knowledge is to be considered partly\nwith reference to the intrinsic importance of the\nsubject, and partly with reference to the par-\nticular necessities of the time in which the\n\nTRANSITION. 151\n\ninquiry is undertaken. In our own case we\nwere forced to keep botli these considerations\nconstantly in view. In the first place we\nhad to state a mass of experiments with our\nconsequent convictions ; next, it was our\nespecial aim to exhibit certain phenomena\n(known, it is true, but misunderstood^ and above\nall, exhibited in false connection,) in that na-\ntural and progressive development which is\nstrictly and truly conformable to observation;\nin order that hereafter, in our polemical or his-\ntorical investigations, we might be enabled to\nbring a complete preparatory analysis to bear\non, and elucidate, our general view. The details\nwe have entered into were on this account\nunavoidable ; they may be considered as a re-\nluctant consequence of the occasion. Hereafter,\nwhen philosophers will look upon a simple\nprinciple as simple, a combined efiect as\ncombined ; when they will acknowledge the\nfirst elementary, and the second complicated\nstates, for what they are ; then, indeed, all this\nstatement piay be abridged to a narrower form ;\na labour which, should we ourselves not be able\nto accomplish it, we bequeath to the active in-\nterest of contemporaries and posterity.\n\nWith respect to the order of the chapters, it\nshould.be remembered that natural phenomena,\n\n152 TBANSITION.\n\nwhich are even allied to each other, are not cod-\nnected in any particular sequence or constant\nseries ; their efficient causes act in a narrow\ncircle, so that it is in some sort indifferent what\nphenomenon is first or last considered ; the main\npoint is, that all should be as far as possible\npresent to us, in order that we may embrace\nthem at last from one point of view, partly ac-\ncording to their nature, partly according to\ngenerally received methods.\n\nYet, in the present particular instance, it may\nbe asserted that the dioptrical colours are justly\nplaced at the head of the physical colours ; not\nonly on account of their striking splendour and\ntheir importance in other respects, but because,\nin tracing these to their source, much was ne-\ncessarily entered into which will assist our sub-\nsequent enquiries.\n\nFor, hitherto, light has been considered as a\nkind of abstract principle, existing and acting\nindependently ; to a certain extent self-modiiied,\nand on the slightest cause, producing colours\nout of itself. To divert the votaries of physical\nscience from this mode of viewing the subject ;\nto make them attentive to the fact, that in pris-\nmatic and other appearances we have not to do\n\nTRANSITION. 153\n\nwith light as an uncircumscribed and modify-*\ning principle, but as circumscribed and modi-\nfied ; that we have to do with a luminous image ;\nwith images or circumscribed objects generally,\nwhether light or dark : this was the purpose we\nhad in view, and such is the problem to be solved.\n\nAll that takes place in dioptrical cases, —\nespecially those of the second class which are\nconnected with the phenomena of refraction, — is\nnow sufficiently familiar to us, and will serve\nas an introduction to what follows.\n\nCatoptrical appearances remind us of the\nptiysit^logical phenomena, but as we ascribe a\nmore objective character to the former, we\nthought ourselves justified in classing them\nwith the physical examples. It is of import-\nance, however, to remember that here again it\nis not light, in an abstract sense, but a luminous\nimage that we have to consider.\n\nIn proceeding onwards to the paroptrical\nclass, the reader, if duly acquainted with the\nforegoing facts, will be pleased to find himself\nonce more in the region of circumscribed forms.\nThe shadows of bodies, especially, as secondary\n\n164 CATOPTBICAL C0L0UB8.\n\nimftges, so exactly -a^aQinpiwyiDg the object,\nwill -serve greatly i to elucidate analogous ap-\n\nWe will not, ibowever, anticipate these state-\nments, but proceed as heretofore in what we\nconsider the regular course.\n\nXXXI.\n\nCATOPTRICAL COLOURS.\n\nCatoptrical colours are such as appear in con-\nsequence, of a minror-like reflectioa. We as-\nsume, in the. first place, that the light itself, ; as\nwell as the surface from which it. is reflected, is\nperfectly colourless. In this sense the appear-\nances in question come under the head of phy-\nsical colours. They arise in consequence of\nreflection, as we found the dioptrical colours of\ntbe:i»econd class appear by. means of refraction.\nWithout further general definitions, we turn our\nattention at once to particular cases, and to the\nconditions which are essential to the exhibition\nof. these phenomena.\n\nCATOFTBICAL COLOUBS. 165\n\nIf we unroll a coil of bright steel-wire, and\nafter suflering it to spring confusedly together\nagain, place it at a window in the light, we shall\nsee the prominent parts of the circles and con-\nTolutions illutnined, but neither resplendent\nnor iridescent. But if the sun shines on the\nwire, this light will be condensed into a point,\nand we perceive a small resplendent image of\nthe sun, which, when seen near, exhibits no\ncolour. On retiring a little, however, and fixing\nthe eyes on this refulgent appearance, we dis-\ncern several small mirrored suns, coloured in the\nmost varied manner; and although the impres-\nsion is that green and red predominate, yet, on\na more accurate inspection, we find that the\nother colours are also present.\n\nIf we take an eye-glass, and examine the ap-\npearance through it, we find the colours have\nvanished, as well as the radiating splendour in\nwhich they were seen, and we perceive only the\nsmall luminous points, the repeated images of\nthe sun. We thus find that the impression is\nsubjective in its nature, and that the appear-\nance is allied to those which we have adverted\nto under the name of radiating halos (100).\n\n150 CATOPTaiCAL C0L0V&8.\n\nWe can, however, exhibit this pfaenomenou\nobjectively. Let a piece of white paper be fast-\nened beneath a small aperture in the lid of a\ncamera-obacura, and when the bud shines\nthrough this aperture, let the confiisedly-ruHed\nsteel-wire be held in the light, so that it be op-\nposite to the paper. The sun-light will impinge\non and in the circles of the wire, and will not,\nas in the concentrating lens of the eye, display\nitself in a point ; but, as the paper can receive\nthe reflection of .the light in every part of its\nsurface will be seen in hair-like lines, which are\nalso iridescent.\n\nThis experiment is purely catoptrical ; for as\nwe cannot imagine that the light penetrates the\nsurface of the steel, and thus undergoes a\nchange, we are soon convinced that we have\nhere a mere reflection which, in its subjective\ncharacter, is connected with the tbeoty of faintly\nacting lights, and the after-image of dazzling\nlights, and as far as it can be considered ob-\njective, announces even in the minutest appear-\nances, a real eifect, independent of the action\nand reaction of the eye.\n\nWe have seen that to produce these eflects\n\n!.,\n\nCATOPTRICAL COLOURS. 157\n\nQOt merely light but a powerful light is neces-\n•aiy; that this powerful light again is not an\nabstract and general quality, but a circumscribed\nlight, a luminous image. We can convince our-\naelves still further of this by analogous cases.\n\nA polished surface of silver placed in the sun\nleflects a dazzling light, but in this case no\ncolour is seen. If, however, we slightly scratch\n4l6 surface, an iridescent appearance, in which\ngreen and red are conspicuous, will be exhibited\n; at a certain angle. In chased and carved\nmetals the effect is striking : yet it may be re-\nmarked throughout that, in order to its appear-\nance, some form, some alternation of light and\ndark must co-operate with the reflection ; thus\na window-bar, the stem of a tree, an accident-\nally or purposely interposed object produces a\nperceptible effect. This appearance, too, may\nbe exhibited objectively in the camera-obscura.\n\nIf we cause a polished plated surface to be so\nacted on by aqua fortis that the copper within is\ntouched, and the surface itself thus rendered\nrough, and if the sun's image .be then reflected\nfrom it, the splendour will be reverberated from\nevery minutest prominence, and the surface will\nappear iridescent. So, if we hold a sheet of\n\nIS6 CATOPraiCAL OOUHTSft.\n\nMack nnglazed paper in tiie son, and look at it\nattentively, it will be seen to glistm in its qii-\nnotest points with the most yhrid oolonfs.\n\nAll these examples are referable to the same\nconditions. In the first case the luminous\nimage is reflected from a thin line ; in the\nsecond probably from sharp edges ; in the third\nfirom very small points. In all a very powerful\nand circumscribed light is requisite. For all\nthese appearances of colour again it is necessary\nthat the eye should be at a due distance firom\nthe reflecting points.\n\nIf these observations are made with the mi-\ncroscope, the appearance will be greatly in-\ncreased in force and splendour, for we then see\nthe smallest portion of the surfaces, lit by the\nsun^ glittering in these colours of reflection,\nwhich, allied to the hues of refraction, now\nattain their highest degree of brilliancy. In\nsuch cases we may observe a vermiform iri-\ndescence on the surface of organic bodies, the\nfurther description of which will be given h^^-\nafter.\n\nLastly, the colours which are chiefly exhi-\n\nCATOPTfttCAL COLOtTM. 159\n\nbhed it! reflection are red and green, whenee\nwe may infer that the linear appearance espe^-\nciailly consists of a thin line of red, bounded by\nblue on one side and yellow on the other. If\nthese triple lines approach very near together,\nthe intermediate space must appear green; a\nphenomenon which will often occur to us as we\nproceed.\n\nWe frequently meet with these colours in\nnature. The colours of the spider's web might\nbe considered exactly of the same class with\nthose reflected from the steel wire, ex<;ept that\nthe non-translucent quality of the former is not\nso certain as in the case of steel ; on which ac-\ncount some have been inclined to class the\ncolours of the spidei^s* web with the p^henomeniok\nof refraction.\n\nIn mother-of-pearl we perceive infinitely fine\norganic fibres and lamellae in juxta-position,\nfrom which, as from the scratched silver before\nalluded to, varied colours, but especially red and\ngrben, may arise.\n\nThe changing colours of the plumage of birds\nmay also be mentioned here, although in all or-\n\n160 CATOPTRICAL COLOURS.\n\nganic instances a chemical principle and an\nadaptation of the colour to the structure may be\nassumed ; considerations to which we shall re-\nturn in treating of chemical colours.\n\nThat the appearances of objective halos also\napproximate catoptrical phenomena will be\nreadily admitted, while we again do not deny\nthat refraction as well may here come into\nthe account. For the present we restrict our-\nselves to one or two observations ; hereafter we\nmay be enabled to make a fuller application of\ngeneral principles to particular examples.\n\nWe first call to mind the yellow and red\ncircles produced on a white or grey wall by a\nlight placed near it (88). Light when reflected\nappears subdued, and a subdued light excites\nthe impression of yellow, and subsequently of\nred.\n\nLet the wall be illumined by a candle placed\nquite close to it. The farther the light is dif-\nfused the fainter it becomes ; but it is still the\neffect of the flame, the continuation of its\naction, the dilated effect of its image. We\nmight, therefore, very fairly call these circles\n\nCATOPTRIC AL COLOURS. 161\n\nreiterated images, because they constitute the\nsuccessive boundaries of the action of the light,\nand yet at the same time only present an ex-\ntended image of the flame.\n\nIf the sky is white and luminous round the\nsun owing to the atmosphere being filled with\nlight vapours; if mists or clouds pass be-\nfore the moon, the reflection of the disk mir-\nrors itself in them ; the halos we then perceive\nare single or double, smaller or greater, some-\ntimes very large, often colourless, sometimes\ncoloured.\n\nI witnessed a very beautiful halo round the\nmoon the 15th of November, 1799, when the\nbarometer stood high ; the sky was cloudy and\nvapoury. The halo was completely coloured,\nand the circles were concentric round the light\nas in subjective halos. That this halo was ob-\njective I was presently convinced by covering\nthe moon's disk, when the same circles were\nnevertheless perfectly visible.\n\nThe different extent of the halos appears to\nhave a relation with the proximity or distance\nof the vapour from the eye of the observer.\n\n162 CATOPTRIC AL COLOURS.\n\nAs window-panes lightly breathed upon in-\ncrease the brilliancy of subjective halos, and in\nsome degree give them an objective character,\nso, perhaps, with a simple contrivance in winter,\nduring a quickly freezing temperature, a more\nexact definition of this might be arrived at.\n\nHow much reason we have in~ considering\nthese circles to insist on the image and its\neffects, is apparent in the phenomenon of the\nso-called double suns. Similar double images\nalways occur in certain points of halos and\ncircles, and only present in a circumscribed\nform what takes place in a more general way in\nthe whole circle. All this will be more conve-\nniently treated in connexion with the appear-\nance of the rainbow. — Note Q.\n\nIn conclusion it is only necessary to point out\nthe affinity between the catoptrical and parop-\ntical colours.\n\nWe call those paroptical colours which ap-\npear when the light passes by the edge of an\nopaque colourless body. How nearly these are\nallied to the dioptrical colours of the second\nclass will be easily seen by those who are con-\nvinced with us that the colours of refraction\n\nGATOPTRICAL COLOURS. 163\n\ntake place only at the edges of objects. The\naffinity again between the catoptrical and par-\noptical colours will be evident in the following\nchapter.\n\nXXXII.\n\nPAROPTICAL COLOURS.\n\nThe paroptical colours have been hitherto called\nperi-optical» because a peculiar effect of light\nwas supposed to take place as it were round the\nobject, and was ascribed to a certain flexibility\nof the light to and from the object.\n\nThese colours again may be divided into sub-\njective and objective, because they appear\npartly without us, as it were, painted on sur-\nfaces, and partly within us, immediately on the\nretina. In this chapter we shall find it more to\nour purpose to take the objective cases first,\nsince the subjective are so closely connected\nwith other appearances already known to us,\nthat it is hardly possible to separate them.\n\nThe paroptical colours then are so called he-\nld 2\n\n164 ' PAROPTICAL COLOURS. .\n\ncause the light must pass by an outline or edge\nto produce them. They do not, however, always\nappear in this case ; to produce the effect very\nparticular conditions are necessary besides.\n\nIt is also to be observed that in this instance\nagain light does not act as an abstract diffusion\n(361), the sun shines towards an edge. The\nvolume of light poured from the sun-image\npasses by the edge of a substance, and occasions\nshadows. Within these shadows we shall pre-\nsently find colours appear.\n\nBut, above all, we should make the experi-\nments and observations that bear upon our pre-\nsent inquiry in the fullest light. We, there-\nfore, place the observer in the open air before\nwe conduct him to the limits of a dark room.\n\nA person walking in sun-shine in a garden, or\non any level path, may observe that his shadow\nonly appears sharply defined next the foot on\nwhich he rests ; farther from this point, espe-\ncially round the head, it melts away into the\nbright ground. For as the sun-light proceeds\nnot only from the middle of the sun, but also\nacts cross- wise from the two extremes of every\n\nPABOPTICAL COLOURS. 16$\n\ndiameter, an objectiye parallax takes place\nwhich produces a half-shadow on both sides of\nthe object.\n\nIf the person walking raises and spreads his\nhandy he distinctly sees in the shadow of each\nfinger the diverging separation of the two half-\nshadows outwards, and the diminution of the\nprincipal shadow inwards, both being efiects of \"\nthe cross action of the light.\n\nThis experiment may be repeated and varied\nbefore a smooth wall, with rods of difierent\nthicknesses, and again with balls ; we shall\nalways find that the farther the object is re-\nmoved from the surface of the wall, the more\nthe weak double shadow spreads, and the more\nthe forcible main shadow diminishes, till at last\nthe main shadow appears quite efiaced, and\neven the double shadows become so faint, that\nthey almost disappear ; at a still greater dis-\ntance they are, in fact, imperceptible.\n\nThat this is caused by the cross- action of the\nlight we may easily convince ourselves ; for the\nshadow of a pointed object plainly exhibits two\npoints. We must thus never lose sight of the\n\n166 PAROPTICAL COLOURS.\n\nfact that in this case the whole sun-image acts,\nproduces shadows, changes them to double\nshadows, and finally obliterates them.\n\nInstead of solid bodies let us now take open-\nings cut of various given sizes next each other,\nand let the sun shine through them on a plane\nsurface at some little distance ; we shall find\nthat the bright image produced by the sun on\nthe surface, is larger than the opening ; this is\nbecause one edge of the sun shines towards the\nopposite edge of the opening, while the other\nedge of the disk is excluded on that side.\nHence the bright image is more weakly lighted\ntowards the edges.\n\nIf we take square openings of any size we\nplease, we shall find that the bright image on a\nsurface nine feet from the opening, is on every\nside about an inch larger than the opening ;\nthus nearly corresponding with the angle of the\napparent diameter of the sun.\n\nThat the brightness should gradually diminish\ntowards the edges of the image is quite natural,\nfor at last only a minimum of the light can act\ncross-wise from the sun's circumference through\nthe edge of the aperture.\n\nFABOPTIGAL GOLOUBS. 167\n\nThus we here again see how much reason we\nhave in actual observation to guard against the\nassumption of parallel rays, bundles and fasces\nof rays> and the like hypothetical notions.\n\nWe might rather consider the splendour of\nthe sun» or of any light, as an infinite specular\nmultiplication of the circumscribed luminous\nimage/ whence it may be explained that all\nsquare openings through which the sun shines,\nat certain distances, according as the apertures\nare greater or smaller, must give a round image\nof light.\n\nThe above experiments may be repeated\nthrough openings of various shapes and sizes,\nand the same effect will always take place at\nproportionate distances. In all these cases, how*\never, we may still observe that in a full light\nand while the sun merely shines past an edge,\nno colour is apparent.\n\nWe therefore proceed to experiments with a\nsubdued light, which is essential to the appear-\nance of colour. Let a small opening be made in\nthe window-shutter of a dark room; let the\n\n168 Varoptical colours.\n\ncrossing sun-light which enters, be received on\na surface of white paper^ and we shall find that\nthe smaller the opening is, the dimmer the light\nimage will be. This is quite obvious, because\nthe paper does not receive light from the whole\nsun, but partially from single points of its disk.\n\nIf we look attentively at this dim image of\nthe sun, we find it still dimmer towards the out-\nlines where a yellow border is perceptible. The\ncolour is still more apparent if a vapour or a\ntransparent cloud passes before the sun, thus\nsubduing and dimming its brightness. The\nhalo on the wall, the efiect of the decreasing\nbrightness of a light placed near it, is here\nforced on our recollection. (88.)\n\nIf we examine the image more accurately, we\nperceive that this yellow border is not the only\nappearance of colour; we can see, besides, a\nbluish circle, if not even a halo-like repetition\nof the coloured border. If the room is quite\ndark, we discern that the sky next the sun also\nhas its effect : we see the blue sky, nay, even\nthe whole landscape, on the paper, and are thus\nagain convinced that as far as regards the\nsun, we have here only to do with a luminous\nimage.\n\nPAROPTICAL C0L0UB8. 169\n\nIf we take a somewhat larger square opening,\nso large that the image of the sun shining\nthrough it does not immediately become round,\nwe may distinctly observe the half-shadows of\nevery edge or side, the junction of these in the\ncorners, and their colours ; just as in the above-\nmentioned appearance with the round opening.\n\nWe have now subdued a parallactic light\nby causing it to shine through small apertures,\nbut we have not taken from it its parallactic\ncharacter; so that it can produce double shadows\nof bodies, although with diminished power.\nThese double shadows which we have hitherto\nbeen describing, follow each other in light and\ndark, coloured and colourless circles, and pro-\nduce repeated, nay, almost innumerable halos.\nThese effects have been often represented in\ndrawings and engravings. By placing needles,\nhairs, and other small bodies, in the subdued\nlight, the numerous halo-like double shadows\nmay be increased ; thus observed, they have\nbeen ascribed to an alternating flexile action\nof the light, and the same assumption has been\nemployed to explain the obliteration of the\ncentral shadow, and the appearance of a light\nin the place of the dark.\n\n170 FABOFTICJU. COLODBS.\n\nFor ourseWes, we maintain that these again\nare parallactic double shadows, which appear\nedged with coloured borders and halos.\n\nAfter having seen and investigated the fore-\ngoing phenomena, we can proceed to the ex-\nperiments with knife-blades,* exhibiting eflfects\nwhich may be referred to the contact and paral-\nlactic mutual intersection of the half-shadows\nand halos already familiar to us.\n\nLastly, the observer may follow out the ex-\nperiments with hairs, needles, and wires, in the\nhalf-light produced as before described by the\nsun, as well as in that derived from the blue\nsky, and indicated on the white paper. He will\nthus make himself still better acquainted with\nthe true nature of this phenomenon.\n\nBut since in these experiments everything\ndepends on our being persuaded of the paral-\nlactic action of the light, we can make this\nmore evident by means of two sources of light,\nthe two shadows from which intersect each\nother, and may be altogether separated. By\nday this may be contrived with two small\n* See Newton'i Optica, book iii.\n\nPAROPTICAL C0L0UB8. 171\n\nopenings in a window-shutter; by night, with\ntwo candles. There are even accidental effects\nin interiors, on opening and closing shutters, by\nmeans of which we can better observe these ap-\npearances than with the most careful apparatus.\nBut still, all and each of these may be reduced\nto experiment by preparing a box which the\nobserver can look into from above, and gradually\ndiminishing the openings after having caused a\ndouble light to shine in. In this case, as might\nbe expected, the coloured shadow, considered\nunder the physiological colours, appears very\neasily.\n\nIt is necessary to remember, generally, what\nhas been before stated with regard to the nature\nof double shadows, half-lights, and the like.\nExperiments also should especially be made\nwith different shades of grey placed next each\nother, where every stripe will appear light by a\ndarker, and dark by a lighter stripe next it. If\nat night, with three or more lights, we produce\nshadows which cross each other successively,\nwe can observe this phenomenon very distinctly,\nand we shall be convinced that the physiological\ncase before more fully treated, here comes into\nthe account (38).\n\nTo what extent the appearances that accom-\n\n172 PABOPTICAL COLOURS.\n\npany the paroptical colours, may be deriired\nfrom the doctrine of subdued lights, from half-\nshadows, and from the physiological disposition\nof the retina, or whether we shall be forced to\ntake refuge in certain intrinsic qualities of light,\nas has hitherto been done, time may teach.\nSuffice it here to have pointed out the con-\nditions under which the paroptical colours ap-\npear, and we may hope that our allusion to\ntheir connexion with the facts before adduced\nby us will not remain unnoticed by the ob-\nservers of nature.\n\nThe affinity of the paroptical colours with the\ndioptrical of the second class will also be readily\nseen and followed up by every reflecting inves-\ntigator. Here, as in those instances, we have\nto do with edges or boundaries; here, as in\nthose instances, with a light, which appears at\nthe outline. How natural, therefore, it is to\nconclude that the paroptical effects may be\nheightened, strengthened, and enriched by the\ndioptrical. Since, however, the luminous image\nactually shines through the medium, we can\nhere only have to do with objective cases of re-\nfraction : it is these which are strictly allied to\nthe paroptical cases. The subjective cases of\nrefraction, where we see objects through the\nmedium, are quite distinct from the paroptical.\n\nPABOPTICAL COLOURS. 1 73\n\nWe have already recommended them on ac-\ncount of their clearness and simplicity.\n\nThe connexion between the paroptical colours\nand the catoptrical may be already inferred\nfrom what has been said : for as the catoptrical\ncolours only appear on scratches, points, steel-\nwire, and delicate threads, so it is nearly the\nsame case as if the light shone past an edge.\nThe light must always be reflected from an\nedge in order to produce colour. Here again,\nas before pointed out, the partial action of the\nluminous image and the subduing of the light\nare both to be taken into the account.\n\nWe add but few observations on the subjective\nparoptical colours, because these may be classed\npartly with the physiological colours, partly\nwith the dioptrical of the second order. The\ngreater part hardly seem to belong here, but,\nwhen attentively considered, they still difiuse a\nsatisfactory light over the whole doctrine^ and\nestablish its connexion.\n\nIf we hold a ruler before the eyes so that the\nflame of a light just appears above it, we see\nthe ruler as it were indented and notched at the\n\n174 PAROPTICAL COLOURS.\n\nplace where the light appears. This seems de-\nducible from the expansive povrer of light acting\non the retina (18).\n\nThe same phenomenon on a large scale is ex-\nhibited at sun-rise ; for when the orb appears\ndistinctly, but not too powerfully, so that we can\nstill look at it, it always makes a sharp indent-\nation in the horizon.\n\nIf, when the sky is grey, we approach a win*\ndow, so that the dark cross of the window-bars\nbe relieved on the sky ; if after fixing the eyes\non the horizontal bar we bend the head a little\nforward ; on half closing the eyes as we look up,\nwe shall presently perceive a bright yellow-red\nborder under the bar, and a bright light-blue\none above it. The duller and more monotonous\nthe grey of the sky, the more dusky the room,\nand, consequently, the more previously unex-\ncited the eye, the livelier the appearance will\nbe ; but it may be seen by an attentive observer\neven in bright daylight.\n\nIf we move the head backwards while half\nclosing the eyes^ so that the horizontal bar be\nseen below, the phenomenon will appear re-\n\nPAROPTIGAL COLOURS. 1 75\n\n▼ersed. The upper edge will appear yellow,\nthe under edge blue.\n\nSuch observations are best made in a dark\nroom. If white paper is spread before the\nopening where the solar microscope is com-\nmonly fastened, the lower edge of the circle\nwill appear blue, the upper yellow, even while\nthe eyes are quite open, or only by half-closing\nthem so far that a halo no longer appears round\nthe white. If the head is moved backwards the\ncolours are reversed.\n\nThese phenomena seem to prove that the hu-\nmours of the eye are in fact only really achro-\nmatic in the centre where vision takes place,\nbut that towards the circumference, and in un-\nusual motions of the eyes, as in looking hori-\nzontally when the head is bent backwards or\nforwards, a chromatic tendency remains, espe-\ncially when distinctly relieved objects are thus\nlooked at. Hence such phenomena may be\nconsidered as allied to the dioptrical colours of\nthe second class.\n\nSimilar colours appear if we look on black\nand white objects, through a pin-hole in a card.\n\n176 PAROPTICAL COLOURS.\n\nInstead of a white object we may take the mi-\nnute light aperture in the tin pliate of a camera\nobscura, as prepared for paroptical experi-\nments.\n\nIf we look through a tube, the farther end of\nwhich is contracted or variously indented, the\nsame colours appear.\n\nThe following phenomena appear to me to be\nmore nearly allied to the paroptical appear-\nances. If we hold up a needle near the eye,\nthe point appears double. A particularly re-\nmarkable effect again is produced if we look\ntowards a grey sky through the blades of knives\nprepared for paroptical experiments. We seem\nto look through a gauze ; a multitude of threads\nappear to the eye ; these are in fact only the\nreiterated images of the sharp edges, each of\nwhich is successively modified by the next, or\nperhaps modified in a parallactic sense by the\noppositely acting one, the whole mass being\nthus changed to a thread-like appearance.\n\nLastly, it is to be remarked that if we look\nthrough the blades towards a minute light in\n\nPAROPTICAL COLOURS. 177\n\nthe window-Bhutter, coloured stripes and halos\nappear on the retina as on the paper.\n\nThe present chapter may be here terminated,\nthe less reluctantly, as a friend has undertaken\nto investigate this subject by further experi-\nments. In our recapitulation, in the descrip-\ntion of the plates and apparatus, we hope here^\nafter to give an account of his observations.*\n\nXXXIIl.\n\nEPOPTICAL COLOURS.\n\nWe have hitherto had to do with colours which\nappear with vivacity, but which immediately\nvanish again when certain conditions cease.\nWe have now to become acquainted with others,\nwhich it is true are still to be considered as\ntransient, but which, under certain circum-\nstances, become so fixed that, even after the\nconditions which first occasioned their appear-\nance cease, they still remain, and thus con-\n\n• The observations here alluded to never appeared.\n\nN\n\n178 EPOPTICAL COLOURS.\n\nstitute the link between the physical and the\nchemical colours.\n\nThey appear from various causes on the sur-\nface of a colourless body, originally, without\ncommunication, die or immersion Oa^^) ; and\nwe now proceed to trace them, from their faint-\nest indication to their most permanent state,\nthrough the different conditions of their appear-\nance, which for easier survey we here at once\nsummarily state.\n\nFirst condition. — ^The contact of two smooth\nsurfaces of hard transparent bodies.\n\nFirst case : if masses or plates of glass, or if\nlenses are pressed against each other.\n\nSecond case : if a crack takes place in a\nsolid mass of glass, chrystal, or ice.\n\nThird case : if lamellae of transparent stones\nbecome separated.\n\nSecond condition. — If a surface of glass or a\npolished stone is breathed upon.\n\nThird condition. — ^The combination of the\ntwo last ; first, breathing on the glass, then\nplacing another plate of glass upon it, thus ex-\nciting the colours by pressure ; then removing\nthe upper glairs, upon which the colours begin\nto fade and vanish with the breath.\n\nEPOPTICAL COLOURS. 179\n\nFourth condition. — Bubbles of various liquids,\nsoap, chocolate, beer, wine, fine glass bubbles.\n\nFifth condition. — Very fine pellicles and la-\nmellse, produced by the decomposition -of mine-\nrals and metals. The pellicles of lime> the sur-\nface of stagnant water, especially if impregnated\nwith iron, and again pellicles of oil on water,\nespecially of varnish on aqua fortis.\n\nSixth condition. — If metals are heated ; the\noperation of imparting tints to steel and other\nmetals.\n\nSeventh condition. — If the surface of glass is\nbeginning to decompose.\n\nFirst condition, first case. If two convex\nglasses, or a convex and plane glass, or, best of\nall, a convex and concave glass come in contact,\nconcentric coloured circles appear. The pheno-\nmenon exhibits itself immediately on the slight-\nest pressure, and may then be gradually carried\nthrough various successive states. We will de-\nscribe the complete appearance at once, as we\nshall then be better enabled to follow the differ-\nent states through which it passes.\n\nThe centre is colourless ; where the glasses\nare, so to speak, united in one by the strongest\npressure, a dark grey point appears with a silver\n\n180 EPOPTICAL COLOURS.\n\nwhite space round it : then follow^ in decreasing\ndistances, various insulated rings, all consisting\nof three colours, which are in immediate con-\ntact with each other. Each of these rings, of\nwhich perhaps three or four might be counted,\nis yellow on the inner side, blue on the outer,\nand red in the centre. Between two rings there\nappears a silver white interval. The rings\nwhich are farthest from the centre are always\nnearer together : they are composed of red and\ngreen without a perceptible white space be-\ntween them.\n\nWe will now observe the appearances in their\ngradual formation, beginning from the slightest\npressure.\n\nOn the slightest pressure the centre itself ap-\npears of a green colour. Then follow as far as\nthe concentric circles extend, red and green\nrings. They are wide, accordingly, and no trace\nof a silver white space is to be seen between\nthem. The green is produced by the blue of an\nimperfectly developed circle, mixing with the\nyellow of the first circle. All the remaining\ncircles are, in this slight contact, broad ; their\nyellow and blue edges mix together, thus pro-\nducing a beautiful green. The red, however, of\n\nEPOPTICAL COLOURS. 181\n\neach circle, remains pure and untouched ; hence\nthe whole series is composed of, these two\ncolours.\n\nA somewhat stronger pressure separates the\nfirst circle by a slight interval from the imper-\nfectly developed one : it is thus detached,\nand may be said to appear in a complete state.\nThe centre is now a blue point ; for the yellow\nof the first circle is now separated from this\ncentral point by a silver white space. From the\ncentre of the blue a red appears, which is thus,\nin all cases, bounded on the outside by its blue\nedge. The second and third rings from the\ncentre are quite detached. Where deviations\nfrom this order present themselves, the observer\nwill be enabled to account for them, from what\nhas been or remains to be stated.\n\nOn a stronger pressure the centre becomes\nyellow ; this yellow is surrounded by a red and\nblue edge : at last, the yellow also retires from\nthe centre ; the innermost circle is formed and\nis bounded with yellow. The whole centre itself\nnow appears silver white, till at last, on the\nstrongest pressure, the dark point appears, and\nthe phenomenon, as described at first, is com^\nplete.\n\n182 EPOPTICAX COLOURS.\n\nThe relative size of the concentric circles and\ntheir intervals depends on the form of the\nglasses which are pressed together.\n\nWe remarked above, that the coloured centre\nis, in fact, an undeveloped circle. It is, how-\never, often found, on the slightest pressure, that\nseveral undeveloped circles exist there, as it\nwete, in the germ; these can be successively\ndeveloped before the eye of the observer.\n\nThe regularity of these rings is owing to the\nform of the convex glasses, and the diameter of\nthe coloured appearance depends on the greater\nor lesser section of a circle on which a lens is\npolished. We easily conclude from this, that\nby pressing plane glasses together, irregular\nappearances only will be produced ; the colours,\nin fact, undulate like watered silks, and spread\nfrom the point of pressure in all directions. Yet,\nthe phenomenon as thus exhibited is much more\nsplendid than in the former instance, and cannot\nfail to strike every spectator. If we make the\nexperiment in this mode, we shall distinctly see,\nas in the other case, that, on a slight pressure,\nthe green and red waves appear ; on a stronger,\nstripes of blue, red, and yellow, become de«\n\nEPOPTJCAL COLOURS. 183\n\ntached. At first, the outer sides of these stripes\ntouch ; on increased pressure they are separated\nby a silver white space.\n\nBefore we proceed to a further description of\nthis phenomenon, we may point out the most\nconvenient mode of exhibiting it. Place 9, large\nconvex glass on a table near the window ; upon\nthis glass lay a plate of well-polished mirror-\nglass, about the size of a playing-card, and the\nmere weight of the plate will press sufficiently\nto produce one or other of the phenomena above\ndescribed. So, also, by the difierent weight of\nplates of glass, by other accidental circum-\nstances, for instance, by slipping the plate on\nthe side of the convex glass where the pressure\ncannot be so strong as in the centre, all the\ngradations above described can be produced in\nsuccession.\n\nIn order to observe the phenomenon it is\nnecessary to look obliquely on the surface where\nit appears. But, above all, it is to be remarked\nthat by stooping still more, and looking at the\nappearance under a more acute angle, the\ncircles not only grow larger but other circles are\ndeveloped from the centre, of which no trace is\nto be discovered when we look perpendicularly,\neven through the strongest magnifiers.\n\n184 ' EPOPTICAL COLOURS.\n\nIn order to exhibit the phenomenon in its\ngreatest beauty, the utmost attention should be\npaid to the cleanness of the glasses. If the ex-\nperiment is made with plate-glass adapted for\nmirrors, the glass should be handled with gloves.\nThe inner surfaces, which must come in contact\nwith the utmost nicety, may be most conve-\nniently cleaned before the experiment, and the\nouter surfaces should be kept clean while the\npressure is increased.\n\nFrom what has been said it will be seen that\nan exact contact of two smooth surfaces is\nnecessary. Polished glasses are best adapted\nfor the purpose. Plates of glass exhibit the\nmost brilliant colours when they fit closely\ntogether, and for this reason the phenomenon\nwill increase in beauty if exhibited under an\nair-pump, by exhausting the air.\n\nThe appearance of the coloured rings may be\nproduced in the greatest perfection by placing a\nconvex and concave glass together which have\nbeen ground on similar segments of circles. I\nhave never seen the efiect more brilliant than\nwith the object-glass of an achromatic telescope,\n\nEPOPTICAL COLOURS. 185\n\nId which the crown-glass and flint-glass were\nnecessarily in the closest contact,\n\nA remarkable appearance takes place when\ndissimilar surfaces are pressed together; for\nexample, a polished crystal and a plate of\nglass. The appearance does not at all exhibit\nitself in large flowing waves, as in the combina-\ntion of glass with glass, but it is small and\nangular, and, as it were, disjointed: thus it\nappears that the surface of the polished crystal,\nwhich consists of infinitely small sections of\nlamellae, does not come so uninterruptedly in\ncontact with the glass as another glass-plate\nwould.\n\nThe appearance of colour vanishes on the\nstrongest pressure, which so intimately unites\nthe two surfaces that they appear to make but\none substance. It is this which occasions the\ndark centre, because the pressed lens no longer\nreflects any light from this point,' for the very\nsame point, when seen against the light, is per-\nfectly clear and transparent. On relaxing the\npressure, the colours, in like manner, gradually\ndiminish, and disappear entirely when the sur-\nfaces are separated.\n\n186 EPOPTICAL COLOURS.\n\nThese same appearances occur in two similar\ncases. If entirely transparent masses become\npartially separated, the surfaces of their parts\nbeing still sufficiently in contact, we see the\nsame circles and waves more or less. They may\nbe produced in great beauty by plunging a hot\nmass of glass in water ; the different fissures and\ncracks enabling us to observe the colours in\nvarious forms. Nature often exhibits the same\nphenomena in split rock crystals.\n\nThis appearance, again, frequently displays\nitself in the mineral world in those kinds of\nstone which by nature have a tendency to ex-\nfoliate. These original lamellae are, it is true,\nso intimately united, that stones of this kind\nappear altogether transparent and colourless,\nyet, the internal layers become separated, from\nvarious accidental causes, without altogether\ndestroying the contact: thus the appearance,\nwhich is now familiar to us by the foregoing\ndescription, often occurs in nature, particularly\nin calcareous spars; the specularis, adularia,\nand other minerals of similar structure. Hence\nit shows an ignorance of the proximate causes\nof an appearance so often accidentally produced,\nto consider it so important in mineralogy, and\nto attach especial value to the specimens ex-\nhibiting it.\n\nEPOPTICAL COLOURS. 187\n\nWe have yet to speak of the very remarkable\ninversion of this appearance, as related by men\nof science. If, namely, instead of looking at\nthe colours by a reflected lights we examine\nthem by a transmitted light, the opposite colours\nare said to appear, and in a mode corresponding\nwith that which we have before described as\nphysiological ; the colours evoking each other.\nInstead of blue, we should thus see red-yellow ;\ninstead of red, green, &c«, and vice versd. We\nreserve experiments in detail^ the rather as we\nhave ourselves still some doubts on this point.\n\nIf we were now called upon to give some ge-\nneral explanation of these epoptical colours, as\nthey appear under the first condition, and to\nshow their connexion with the previously de-\ntailed physical phenomena, we might proceed to\ndo so as follows : —\n\nThe glasses employed for the experiments are\nto be regarded as the utmost possible practical\napproach to transparence. By the intimate\ncontact, however, occasioned by the pressure\napplied to them, their surfaces, we are per-\nsuaded, immediately become in a very slight\ndegree dimmed. Within this semi- transparence\n\n188 EPOPTICAL COLOURS.\n\nthe colours immediately appear, and every circle\ncomprehends the whole scale ; for when the two\noppositeSy yellow and blue, are united by their\nred extremities, pure red appears : the green,\non the other hand, as in prismatic experiments,\nwhen yellow and blue touch.\n\nWe have already repeatedly found that where\ncolour exists at all, the whole scale is soon\ncalled into existence ; a similar principle may be\nsaid to lurk in the nature of every physical\nphenomenon ; it already follows, from the idea\nof polar opposition, from which an elementary\nunity or completeness results.\n\nThe fact that a colour exhibited by trans-\nmitted light is different from that displayed by\nreflected light, reminds us of those dioptrical\ncolours of the first class which we found were\nproduced precisely in the same way through\nsemi-opacity. That here, too, a diminution of\ntransparency exists there can scarcely be a\ndoubt ; for the adhesion of the perfectly smooth\nplates of glass (an adhesion so strong that they\nremain hanging to each other) produces a de-\ngree of union which deprives each of the two\nsurfaces, in some degree, of its smoothness and\ntransparence. The fullest proof may, however.\n\nEPOPTICAL COLOURS. ' 189\n\nbe found in the fact that in the centre, where\nthe lens is most strongly pressed on the other\nglass, and where a perfect union is accom-\nplished, a complete transparence takes place,\nin which we no longer perceive any colour. All\nthis may be hereafter confirmed in a recapitula-\ntion of the whole.\n\nSecond condition. — If after breathing on a\nplate of glass, the breath is merely wiped away\nwith the finger, and if we then again imme-\ndiately breathe on the glass, we see very vivid\ncolours gliding through each other; these, as\nthe moisture evaporates, change their place,\nand at last vanish altogether. If this operation\nis repeated, the colours are more vivid and\nbeautiful, and remain longer than they did the\nfirst time.\n\nQuickly as this appearance passes, and con-\nfused as it appears to be, I have yet remarked\nthe following effects : — At first all the principal\ncolours appear with their combinations ; on\nbreathing more strongly, the appearance may\nbe perceived in some order. In this succession\nit may be remarked, that when the breath in\nevaporating becomes contracted from all sides\n\n190 EPOPTICAL COLOURS.\n\ntowards the centre, the blue colour vanishes\nlast\n\nThe phenomenon appears most readily between\nthe minute lines, which the action of passing\nthe fingers leaves on the clear surface ; a some-\nwhat rough state of the surface of the glass is\notherwise requisite. On some glass the appear-\nance may be produced by merely breathing ; in\nother cases the wiping with the fingers is neces-\nsary : I have even met with polished mirror-\nglasses, one side of which immediately showed\nthe colours vividly; the other not. To judge\nfrom some remaining pieces, the former was ori-\nginally the front of the glass, the latter the side\nwhich was covered with quicksilver.\n\n^ 458.\n\nThese experiments may be best made in cold\nweather, because the glass may be more quickly\nand distinctly breathed upon, and the breath\nevaporates more suddenly. In severe frost the\nphenomenon may be observed on a large scale\nwhile travelling in a carriage ; the glasses being\nwell cleaned, and all closed. The breath of the\npersons within is very gently difiused over the\nglass, and immediately produces the most vivid\nplay of colours. How far they may present a\nregular succession I have not been able to re-\n\nEPOPTICAL COLOURS. 191\n\nmark ; but they appear particularly vivid when\nthey have a dark object as a background. This\nalternation of colours does not, however, last\nlong; for as soon as the breath gathers in\ndrops, or freezes to points of ice, the appear*\nance is at once at an end.\n\nThird condition. — ^The two foregoing experi-\nments of the pressure and breathing may be\nunited ; namely, by breathing on a plate of glass,\nand immediately after pressing the other upon it^\nThe colours then appear as in the case of two\nglasses unbreathed upon, with this difference,\nthat the moisture occasions here and there an\ninterruption of the undulations. On pushing\none glass away from the other the moisture ap«\npears iridescent as it evaporates.\n\nIt might, however, be asserted that this com-\nbined experiment exhibits no more than each\nsingle experiment; for it appears the colours\nexcited by pressure disappear in proportion as\nthe glasses are less in contact, and the moisture\nthen evaporates with its own colours.\n\nFourth condition . — Iridescent appearances\nare observable in almost all bubbles ; soap-\n\n192 EPOPTICAL COLOURS.\n\nbubbles are the most commonly known, and the\neffect in question is thus exhibited in the easiest\nmode ; but it may be observed in wine, beer, in\npure spirit, and again, especially, in the froth of\nchocolate*\n\nAs in the above cases we required an infi-\nnitely narrow space between two surfaces which\nare in contact, so we can consider the pellicle of\nthe soap-bubble as an infinitely thin lamina be-\ntween two elastic bodies ; for the appearance in\nfact takes place between the air within, which\ndistends the bubble, and the atmospheric air.\n\nThe bubble when first produced is colourless ;\nthen coloured stripes, like those in marble\npaper, begin to appear : these at length spread\nover the whole surface, or rather are driven\nround it as it is distended.\n\nIn a single bubble, suffered to hang from the\nstraw or tube, the appearance of colour is diffi-\ncult to observe, for the quick rotation prevents\nany accurate observation, and all the colours\nseem to mix together ; yet we can perceive that\nthe colours begin at the orifice of the tube. The\nsolution itself may, however, be blown into care-\n\nEP0FTICAI4 COLOURS, 193\n\nfully, so that only one bubble shall appear. This\nremains white (colourless) if not much agitated ;\nbut if the solution is not too watery, circles ap-\npear round the perpendicular axis of the bubble;\nthese being near each other, are commonly com-\nposed alternately of green and red. Lastly,\nseveral bubbles may be produced together by\nthe same means ; in this case the colours appear\non the sides where two bubbles have pressed\neach other flat.\n\nThe bubbles of chocolate-froth may perhaps\nbe even more conveniently observed than those\nof soap; though smaller, they remain longer.\nIn these, owing to the heat, an impulse, a move-\nment, is produced and sustained, which appears\nnecessary to the development and succession\nof the appearances.\n\nIf the bubble is small, or shut. in between\nothers, coloured lines chase each other over the\nsurface, resembling marbled paper ; all the co-\nlours of the scale are seen to pass through each\nother ; the pure, the augmented, the combined,\nall distinctly clear and beautiful. In small\nbubbles the appearance lasts for a considerable\ntime.\n\no\n\n194 EPOFTICAL COLOUBS/\n\nIf the bubble is larger, or if it becomes by\ndegrees detached, owing to the bursting of others\nnear, we perceive that this impulsion and at-\ntraction of the colours has, as it were, an end in\nview ; for on the highest point of the bubble we\nsee a small circle appear, which is yellow in the\ncentre ; the other remaining coloured lines move\nconstantly round this with a vermicular action.\n\nIn a short time the circle enlarges and sinks\ndownwards on all sides; in the centre the\nyellow remains; below and on the outside it\nbecomes red, and soon blue ; below this again ap-\npears a new circle of the same series of colours :\nif they approximate sufficiently, a green is pro-\nduced by the union of the border-colours.\n\nWhen I could count three such leading cir-\ncles, the centre was colourless, and this space\nbecame by degrees larger as the circles sank\nlower, till at last the bubble burst.\n\nFifth condition. — Very delicate pellicles may\nbe formed in various ways : on these films we\ndiscover a very lively play of colours, either in\nthe usual order, or more confusedly passing\nthrough each other. The water in which lime\n\nBPOPTICAL COLOURS. 195\n\nhas been slaked soon skims over with a coloured\npellicle: the same happens on the surface of\nstagnant water, especially if impregnated with\niron. The lamellae of the fine tartar which\nadheres to bottles, especially in red French\nwine, exhibit the most brilliant colours, on\nbeing exposed to the light, if carefully detached.\nDrops of oil on water, brandy, and other fluids,\nproduce also similar circles and brilliant effects :\nbut the most beautiful experiment that can be\nmade is the following : — Let aqua fortis, not too\nstrong, be poured into a flat saucer, and then\nwith a brush drop on it some of the varnish\nused by engravers to cover certain portions\nduring the process of biting their plates. After\nquick commotion there presently appears a film\nwhich spreads itself out in circles, and imme-\ndiately produces the most vivid appearances of\ncolour.\n\nSixth condition. — When metals are heated,\ncolours rapidly succeeding each other appear on\nthe surface : these colours can, however, be ar-\nrested at will.\n\nIf a piece of polished steel is heated, it will,\nat a certain degree of warmth, be overspread\nwith yellow. If taken suddenly away from the\nfire, this yellow remains.\n\n' o2\n\n196 EPOPTICAL COLOURS.\n\nAs the steel becomes hotter, the yellow ap-\npears darker, intenser, and presently passes into\nred. This is difficult to arrest, for it hastens\nvery quickly to bright blue.\n\nThis beautiful blue is to be arrested if the\nsteel is suddenly taken out of the heat and bu-\nried in ashes. The blue steel works are pro-\nduced in this way. If, again, the steel is held\nlonger over the fire, it soon becomes a light blue,\nand so it remains.\n\nThese colours pass like a breath over the\nplate of steel; each seems to fly before the\nother, but, in reality, each successive hue is\nconstantly developed from the preceding one.\n\nIf we hold a penknife in the flame of a light,\na coloured stripe will appear across the blade.\nThe portion of the stripe which was nearest to\nthe flame is light blue; this melts into blue-\nred ; the red is in the centre ; then follow yellow-\nred and yellow.\n\nThis phenomenon is deducible from the pre-\n\nEPOPTICAL COLOURS. 197\n\nceding ones ; for the portion of the blade next\nthe handle is less heated than the end which is\nin the flanie, and thus all the colours which in\nother cases exhibited themselves in succession,\nmust here appear at once, and may thus be\npermanently preserved.\n\nRobert Boyle gives this succession of colours\nas follows : — \" A florido flavo ad flavum saturum\net rubescentem (quem artifices sanguineum vo-\ncant) inde ad languidum, postea ad saturiorem\ncyaneum.\" This would be quite correct if the\nwords \" languidus\" and \"saturior\" were to change\nplaces. How far the observation is correct, that\nthe different colours have a relation to the de-\ngree of temper which the metal afterwards\nacquires, we leave to others to decide. The\ncolours are here only indications of the different\ndegrees of heat. — Note R.\n\nWhen lead is calcined, the surface is first\ngreyish. This greyish powder, with greater\nheat, becomes yellow, and then orange. Silver,\ntoo, exhibits colours when heated ; the fracture\nof silver in the process of refining belongs to\nthe same class of examples. When metallic\nglasses melt, colours in like manner appear on\nthe surface.\n\n198 EPOPTICAL COLOURS.\n\nSeventh condition. — When the surface of glass\nbecomes decomposed. The accidental opacity\n(blind werden) of glass has been already no-\nticed : the term (blindwerden) is employed to\ndenote that the surface of the glass is so affected\nas to appear dim to us.\n\nWhite glass becomes *' blind\" soonest ; cast,\nand afterwards polished glass is also liable to\nbe so affected ; the bluish less> the green least.\n\nOf the two sides of a plate of glass one is\ncalled the mirror side ; it is that which in the\noven lies uppermost, on which one may observe\nroundish elevations: it is smoother than the\nother, which is undermost in the oven> and on\nwhich scratches may be sometimes observed.\nOn this account the tnirror side is placed facing\nthe interior of rooms, because it is less affected\nby the moisture adhering to it from within, than\nthe other would be, and the glass is thus less\nliable to become \" blind.\"\n\nThis half-opacity or dimness of the glass as-\nsumes by degrees an appearance of colour\nwhich may become very vivid, and in which\n\nEPOPTIGAL COLOUBB. 109\n\nperhaps a certain succesBion^ or otherwise regu-\nlar order, might be discovered\n\nHaving thus traced the physical colours from\ntheir simplest effects to the present instances,\nwhere these fleeting appearances are found to\nbe fixed in bodies, we are, in fact, arrived at the\npoint where the chemical colours begin ; n^y,\nwe have in some sort already passed those limits ;\na circumstance which may excite a favourable\nprejudice for the consistency of our statement.\nBy way of conclusion to this part of our inquiry,\nwe subjoin a general observation, which may\nnot be without its bearing on the common con-\nnecting principle of the phenomena that have\nbeen adduced.\n\n#\n\nThe colouring of steel and the appearances\nanalogous to it, might perhaps be easily deduced\nfrom the doctrine of the semi-opaque mediums.\nPolished steel reflects light powerfully : we may\nconsider the colour produced by the heat as a\nslight degree of dimness : hence a bright yellow\nmust immediately appear ; this, as the dimness\nincreases, must still appear deeper, more con-\ndensed, and redder, and at last pure and ruby-\nred. The colour has now reached the extreme\npoint of depth, and if we suppose the same de-\n\n200 EPOPTICAL COLOURS.\n\ngree of semi-opacity still to continue, the dim-\nness would now spread itself over a dark ground,\nfirst producing a violet, then a dark-blue> and at\nlast a light-blue, and thus complete the series of\nthe appearances.\n\nWe will not assert that this mode of explana-\ntion will suffice in all cases; our object is rather\nto point out the road by which the all-compre-\nhensive formula, the very key of the enigma,\nmay be at last discovered. — Note S.\n\nPART III.\n\nCHEMICAL COLOURS.\n\nWe give this denomination to colours which we\ncan produce, and more or less fix, in certain\nbodies; which we can render more intense,\nwhich we can again take away and communicate\nto other bodies, and to which, therefore, we\nascribe a certain permanency : duration is their\nprevailing characteristic.\n\nIn this view the chemical colours were for*\nmerly distinguished with various epithets ; they\nwere called colores proprii, corporei, materiales,\nveriy permanentes, fijci.\n\nIn the preceding chapter we observed how\nthe fluctuating and transient nature of the phy-\nsical colours becomes gradually fixed, thus\nforming the natural transition to our present\nsubject.\n\nColour becomes fixed in bodies more or less\npermanently ; superficially, or thoroughly.\n\nAll bodies are susceptible of colour ; it can\n\n202 CHEMICAL CONTRAST.\n\neither be excited, rendered intense, and gra-\ndually fixed in them, or at least communicated\nto them«\n\nXXXIV.\n\nCHEMICAL CONTRAST.\n\nIn the examination of coloured appearances we\nhad occasion everywhere to take notice of a\nprinciple of contrast : so again, in approaching\nthe precincts of chemistry, we find a chemical\ncontrast of a remarkable nature* We speak\nhere, with reference to our present purpose,\nonly of that which is comprehended under the\ngeneral names of acid and alkali.\n\nWe characterised the chromatic contrast, in\nconformity with all other physical contrasts as\na more and less ; ascribing the plus to the yellow\nside, the minus to the blue; and we now find\nthat these two divisions correspond with the\nchemical contrasts. The yellow and yellow-red\naffect the acids, the blue and blue-red the\nalkalis ; thus the phenomena of chemical co-\nlours, although still necessarily mixed up with\n\nCHEMICAL C0KTBA8T. 203\n\nOther considerations, admit of being traced with\nsufficient simplicity.\n\nThe principal phenomena in chemical colours\nare produced by the oxydation of metals, and it\nwill be seen how important this consideration is\nat the outset* Other facts which come into the\naccount, and which are worthy of attention, will\nbe examined under separate heads ; in doing\nthis we, however, expressly state that we only\npropose to offer some preparatory suggestions to\nthe chemist in a very general way, without\nentering into the nicer chemical problems and\nquestions, or presuming to decide on them. Our\nobject is only to give a sketch of the mode in\nwhich, according to our conviction, the chemical\ntheory of colours may be connected with general\nphysics.\n\nXXXV.\n\nWHITE.\n\nIn treating of the dioptrical colours of the first\nclass (155) we have already in some degree anti-\ncipated this subject. Transparent substances\n\n200 CH£MICAI» CONTRAST.\n\ntion^ by vinegar, by mild acid fermentatianft ;\nfor example, a decoction of rice, &c.\n\nAgain, it may be inferred that a de-oxydation\nmay produce black. This occurs in the prepa-\nration of ink, which becomes yellow by the\nsolution of iron in strong sulphuric acid, but\nwhen partly de-oxydised by the infusion of gall-\nnuts, appears black.\n\nXXX VII.\n\nFIRST RXCITATION OF COLOUR.\n\nIn the division of physical colours, where semi-\ntransparent mediums were considered, we saw\ncolours antecedently to white and black. In\nthe present case we assume a white and black\nalready produced and fixed ; and the question\nis, how colour can be excited in them ?\n\nHere, too, we can say, white that becomes\ndarkened or dimmed inclines to yellow ; black,\nas it becomes lighter, inclines to blue. — Note U .\n\nFIRST BKOITATION OP COLOUR. 207\n\nYellow appeal's on the active (plus) side, im-\nmediately in the light, the bright, the white.\nAll white surfaces easily assume a yellow tinge ;\npaper, linen, wool, silk, wax : transparent fluids\nagain, which have a tendency to combustion,\neasily become yellow; in other words they\neasily pass into a very slight state of semi- trans-\nparence.\n\nSo again the excitement on the passive side,\nthe tendency to obscure, dark, black, is imme-\ndiately accompanied with blue, or rather with a\nreddish-blue. Iron dissolved in sulphuric acid,\nand much diluted with water, if held to the\nlight in a glass, exhibits a beautiful violet colour\nas soon as a few drops only of the infusion of\ngall-nuts are added. This colour presents the\npeculiar hues of the dark topaz, the orphninon\nof a burnt-red, as the ancients expressed it.\n\nWhether any colour can be excited in the\npure earths by the chemical operations of na-\nture and art, without the admixture of metallic\noxydes, is an important question, generally, in-\ndeed, answered in the negative. It is perhaps\nconnected with the question — to what extent\n\n208 FIRST EXCITATION OF COLOUR.\n\nchanges may be produced in the earths through\noxydation ?\n\nUndoubtedly the negation of the above ques-\ntion is confirmed by the circumstance that\nwherever mineral colours are found, some trace\nof metal^ especially of iron, shows itself; we are\nthus naturally led to consider how easily iron\nbecomes oxydised, how easily the oxyde of iron\nassumes dilBerent colours, how infinitely divisi-\nble it is, and how quickly it communicates its\ncolour. It were to be wished, notwithstanding,\nthat new experiments could be made in regard\nto the above point, so as either to confirm or\nremove any doubt.\n\nHowever this may be, the susceptibility of\nthe earths with regard to colours already existing\nis very great ; aluminous earth is thus particu-\nlarly distinguished.\n\nIn proceeding to consider the metals, which\nin the inorganic world have the almost exclu-\nsive prerogative of appearing coloured, we\nfind that, in their pure, independent, natural\nstate, they are already distinguished from the\n\n/ FIRST EXCITATION OF COLOURS. 209\n\n/\n\nf\n\npure earths by a tendency to some one colour or\nother.\n\nWhile silver approximates most to pure white,\n— nay, really represents pure white, heightened\nby metallic splendor, — steel, tin, lead, and so\nforth, incline towards pale blue-grey ; gold, on\nthe other hand, deepens to pure yellow, copper\napproaches a red hue, which, under certain\ncircumstances, increases almost to bright' red,\nbut which again returns to a yellow golden\ncolour when combined with zinc.\n\nBut if metals in their pure state have so\nspecific a determination towards this or that\nexhibition of colour, they are, through the effect\nof oxydation, in some degree reduced to a com-\nmon character ; for the elementary colours now\ncome forth in their purity, and although this or\nthat metal appears to have a particular tend-\nency to this or that colour, we find some that\ncan go through the whole circle of hues, others,\nthat are capable of exhibiting more than one\ncolour; tin, however, is distinguished by its\ncomparative inaptitude to become coloured.\nWe propose to give a table hereafter, showing\nhow far the different metals can be more or less\nmade to exhibit the different colours.\n\n210 FIRST EXCITATION OF COLOURS.\n\nWhen the clean, smooth surface of a pure\nmetal, on being heated, becomes overspread with\na mantling colour, which passes through a series\nof appearances as the heat increases, this, we are\npersuaded, indicates the aptitude of the metal\nto pass through the whole range of colours. We\nfind this phenomenon most beautifully exhibited\nin polished steel ; but silver, copper, brass, lead,\nand tin, easily present similar appearances. A\nsuperficial oxydation is probably here taking\nplace, as may be inferred from the effects of the\noperation when continued, especially in the\nmore easily oxydizable metals.\n\nThe same conclusion may be drawn from the\nfact that iron is more easily oxydizable by acid\nliquids when it is red hot, for in this case the\ntwo effects concur with each other. We observe,\nagain, that steel, accordingly as it is hardened\nin different stages of its colorification, may ex-\nhibit a difference of elasticity: this is quite\nnatural, for the various appearances of colour\nindicate various degrees of heat.*\n\nIf we look beyond this superficial mantling.\n\n* See par. 478.\n\nFIRST EXCITATION OF COLOURS. 21 1\n\nthis pellicle of colour, we observe that as metals\nare oxydized throughout their masses, white or\nblack appears with the first degree of heat, as\nmay be seen in white lead, iron, and quicksilver.\n\nIf we examine further, and look for the actual\nexhibition of colour, we find it most frequently\non the plus side. The mantling, so often men-\ntioned, of smooth metallic surfaces begins with\nyellow. Iron passes presently into yellow ochre,\nlead from white lead to massicot, quicksilver\nfrom sBthiops to yellow turbith. The solutions'\nof gold and platinum in acids are yellow.\n\nThe exhibitions on the minus side are less fre-\nquent. Coiner slightly oxydized appears blue.\nIn the preparation of Prussian-blue, alkalis are\nemployed.\n\nGenerally, however, these appearances of co-\nlour are of so mutable a nature that chemists\nlook upon them as deceptive tests, at least in\nthe nicer gradations. For ourselves, as we can\nonly treat of these matters in a general way, we\nmerely observe that the appearances of colour\nin metals may be classed according to their\n\np2\n\n212 AUGMENTATION OF COLOUR.\n\norigin^ manifold appearance, and cessation, as\nvarious results of oxydation, hyper-oxydation,\nab-oxydation, and de-oxydation.*\n\nXXXVIII.\n\nAUGMENTATION OF COLOUB-f\n\nThe augmentation of colour exhibits itself as a\ncondensation, a fulness, a darkening of the hue.\nWe have before seen, in treating of colourless\nmediums, that by increasing the degree of opa-\ncity in the medium, we can deepen a bright\nobject from the lightest yellow to the in tensest\nruby-red. Blue, on the other hand, increases\nto the most beautiful violet, if we rarefy and\ndiminish a semi-opaque medium, itself lighted,\nbut through which we see darkness (150, 161).\n\nIf the colour is positive, a similar colour ap-\npears in the intenser state. Thus if we fill a\nwhite porcelain cup with a pure yellow liquor,\nthe fluid will appear to become gradually redder\n\n* As these tenns are afterwards referred to (par. 525), it was\nnecessary to preserve them.\n\nt Steigerung, literally gradual ascent. See the note to par. 523.\n\nAUGMENTATION OF COLOUR. 213\n\ntowards the bottom, and at last appears orange.\nIf we pour a pure blue solution into another\ncup, the upper portion will exhibit a sky-blue,\nthat towards the bottom, a beautiful violet. If\nthe cup is placed in the sun, the shadowed side,\neren of the upper portion, is already violet. If\nwe throw a shadow with the hand, or any\nother substance, over the illumined portion, the\nshadow in like manner appears reddish.\n\nThis is one of the most important appearances\nconnected with the doctrine of colours, for we\nhere manifestly find that a difference of quan-\ntity produces a corresponding qualified impres-\nsion on our senses. In speaking of the last\nclass of epoptical colours (452, 485), we stated\nour conjecture that the colouring of steel might\nperhaps be traced to the doctrine of the semi-\ntransparent mediums, and we would here again\nrecall this to the reader's recollection.\n\nAll chemical augmentation of folour, again,\nis the immediate consequence of continued ex-\ncitation. The augmentation advances constantly\nand unremittingly, and it is to be observed that\nthe increase of intenseness is most common on\nthe plug side. Yellow iron ochre increases, as\nwell by fire as by other operations, to a very\n\n214 AUGMENTATION OF COLOUR.\n\nStrong red: massicot is increased to red lead,\nturbith to vermilion, which last attains a Teiy\nhigh degree of the yellow* red. An intimate\nsaturation of the metal by the acid, and its 6e*\npitration to infinity, take place together with the\nabove effects.\n\nThe augmentation on the minus side is less\nfrequent; but we observe that the more pure\nand condensed the Prussian-blue or cobalt glass\nis prepared, the more readily it assumes a red-\ndish hue and inclines to the violet.\n\nThe French have a happy expression for the\nless perceptible tendency of yellow and blue\ntowards red : they say the colour has \" un ceil\nde rouge,\" which we might perhaps express by\na reddish glance (einen rothlichen blick) .\n\nXXXIX.\n\nCULMINATION*\n\nThis is the consequence of still progressing aug*\nmentation. Red, in which neither yellow nor\n\n* Culmination^ the original word. It might have been ren-\n\nCULMINATION. 215\n\nUue is to be detected, here constitutes the\nacme.\n\nIf we wish to select a striking example of a\nculmination on the plus side, we again find it\nin the coloured steely which attains the bright\nred acme» and can be arrested at this point.\n\nWere we here to employ the terminology be-\nfore proposed, we should say that the first oxy-\ndation produces yellow, the hyper-oxydation\nyellow-red ; that here a kind of maximum exists,\nand that then an ab-oxydation, and lastly a de-\noxydation takes place.\n\nHigh degrees of oxydation produce a bright\nred« Gold in solution, precipitated by a solution\nof tin, appears bright red : oxyde of arsenic, in\ncombination with sulphur, produces a ruby\ncolour.\n\nHow far, however, a kind of sub-oxydation\nmay co-operate in some culminations, is matter\nfor inquiry ; for an influence of alkalis on the\n\ndered maximum of colour^ but aB the author suppOBes an ascent\nthrough yellow and blue to red, his meaning is better expressed\nby his own term.\n\n216 CULMINATION.\n\nyellow-red also appears to produce the culmina*\ntion ; the colour reaching the acme by being\nforced towards the minus side.\n\nThe Dutch prepare a colour known by the\nname of vermilion, from the best Hungarian\ncinnabar, which exhibits the brightest yellow-\nred. This vermilion is still only a cinnabar,\nwhich, however, approximates the pure red, and\nit may be conjectured that alkalis are used to\nbring it nearer to the culminating point.\n\nVegetable juices, treated in this way, offer\nvery striking examples of the above effects.\nThe colouring-matter of turmeric, annotto, dyer's\nsaffron,* and other vegetables, being extracted\nwith spirits of wine, exhibits tints of yellow,\nyellow-red, and hyacinth-red ; these, by the ad-\nmixture of alkalis, pass to the culminating point,\nand even beyond it to blue-red.\n\nNo instance of a culmination on the minus\nside has come to my knowledge in the mineral\nand vegetable kingdoms. In the animal king-\ndom the juice of the murex is remarkable ; of\nits augmentation and culmination on the minus\nside, we shall hereafter have occasion to speak.\n\n* Curcuma, Bixa Orellana, Carthamus Tinctorius.\n\nXL.\n\nFLUCTUATION.\n\nThe mutability of colour is so great, that even\nthose pigments, which may have been considered\nto be defined and arrested, still admit of slight\nvariations on one side or the other. This muta-\nbility is most remarkable near the culminating\npoint, and is effected in a very striking manner\nby the alternate employment of acids and alkalis.\n\nTo express this appearance in dyeing, the\nFrench make use of the word ** virer,\" to turn\nfrom one side to the other; they thus very\nadroitly convey an idea which others attempt to\nexpress by terms indicating the component\nhues.\n\nThe effect produced with litmus is one of the\nmost known and striking of this kind. This\ncolouring substance is rendered red-blue by\nmeanfi of alkalis. The red-blue is very readily\nchanged to red-yellow by means of acids, and\nagain returns to its first state by again employ-\ning alkalis. The question whether a culmi-\nnating point is to be discovered and arrested by\n\n218 FLUCTUATION.\n\nnice experiments, is left to those who are prac-\ntised in these operations. Dyeing, especially\nscarlet-dyeing, might afford a variety of ex-\namples of this fluctuation.\n\nXLI.\n\nPA88AGB THROUGH THB WHOLE 8CALB.\n\nThe first excitation and gradual increase of\ncolour take place more on the phs than on the\nminus side. So, also, in passing through the\nwhole scale, colour exhibits itself most on the\nplus side.\n\nA passage of this kind, regular and evident to\nthe senses, from yellow through red to blue, is\napparent in the colouring of steel.\n\n«\n\nThe metals may be arrested at various points\nof the colorific circle by various degrees and\nkinds of oxydation.\n\nAs they also appear green> a question arises\nwhether chemists know any instance in the\n\nPASSAGE THBOUGH THE WHOLE SCALE. 219\n\nmineral kingdom of a constant transition from\nyellow, through green, to blue, and* vice versd.\nOxyde of iron, melted with glass, produces first\na green, and with a more powerful heat, a blue\ncolour.\n\nWe may here observe of green generally, that\nit appears, especially in an atomic sense, and\ncertainly in a pure state, when we mix blue and\nyellow : but, again, an impure and dirty yellow\nsoon gives us the impression of green ; yellow\nand black already produce green ; this, however,\nis owing to the affinity between black and blue.\nAn imperfect yellow, such as that of sulphur,\ngives us the impression of a greenish hue : thus,\nagain, an imperfect blue appears green. The\ngreen of wine bottles arises, it appears, from an\nimperfect union of the oxyde of iron with the\nglass. If we produce a more complete union\nby greater heat, a beautiful blue-glass is the\nresult.\n\nFrom all this it appears that a certain chasm\nexists in nature between yellow and blue, the\nopposite characters of which, it is true, may be\ndone away atomically by due immixture, and,\nthus combined, to green ; but the true recon-\nciliation between yellow and blue, it seems,\nonly takes place by means of red.\n\n220 PASSAGE THROUGH THE WHOLE SCALE.\n\nThe process, however, which appears un-\nattainable in inorganic substances, we shall find\nto be possible when we turn our attention to\norganic productions ; for in these, the passage\nthrough the whole circle from yellow, through\ngreen and blue, to red, really takes place.\n\nXLII.\n\nINVERSION.\n\nAgain, an immediate inversion of change to\nthe totally opposite hue, is a very remarkable\nappearance which sometimes occurs ; at present,\nwe are merely enabled to adduce what follows.\n\nThe mineral chameleon, a name which has\nbeen given to an oxyde of manganese, may be\nconsidered, in its perfectly dry state, as a green\npowder. If we strew it in water, the green\ncolour displays itself very beautifully in the first\nmoment of solution, but it changes presently to\nthe bright red opposite to green, M'ithout any\napparent intermediate state.\n\nINVEBSION. 221\n\nThe same occurs with the sympathetic ink,\nwhich may be considered a reddish liquid, but\nwhich, when dried by warmth, appears as a\ngreen colour on paper.\n\nIn fact, this phenomenon appears to be owing\nto the conflict between a dry and moist state, as\nhas been already observed, if we are not mis-\ntaken, by the chemists. We may look to the\nimprovements of time to point out what may\nfurther be deduced from these phenomena, and\nto show what other facts they may be connected\nwith.\n\nXLIII.\n\nFIXATION.\n\nMutable as we have hitherto found colour to\nbe, even as a substance, yet under certain cir-\ncumstances it may at last be fixed.\n\nThere are bodies capable of being entirely\nconverted into colouring matter : here it may be\nsaid that the colour fixes itself in its own sub-\n\n223 FIXATION.\n\nstance, stops at a certain point, and is there de*\nfined. Such colouring substances are found\nthroughout nature ; the vegetable world affords\na great quantity of examples, among which\nsome are particularly distinguished, and may be\nconsidered as the representatives of the rest;\nsuch as, on the active side, madder, on the\npassive side, indigo.\n\nIn order to make these materials available in\nuse, it is necessary that the colouring quality in\nthem should be intimately condensed, and the\ntinging substance refined, practically speaking,\nto an infinite divisibility. This is accomplished\nin various ways, and particularly by the well-\nknown means of fermentation and decomposition.\n\nThese colouring substances now attach them-\nselves again to other bodies. Thus, in the\nmineral kingdom they adhere to earths and\nmetallic oxydes; they units in melting with\nglasses ; and in this case, as the light is trans-\nmitted through them, they appear in the greatest\nbeauty, while an eternal' duration may be as-\ncribed to them.\n\nThey fasten on vegetable and animal bodies\nwith more or less power, and remain more or less\n\nFIXATION. 223\n\npermanently ; partly owing to their nature, — as\nyellow, for instance, is more evanescent than\nblue, — or owing to the nature of the substance on\nwhich they appear. They last less in vegetable\nthan in animal substances, and even within this\nlatter kingdom there are again varieties. Hemp\nor cotton threads, silk or wool, exhibit very\ndifferent relations to colouring substances.\n\nHere comes into the account the important\noperation of employing mordants, which may\nbe considered as the intermediate agents be-\ntween the colour and the recipient substance ;\nvarious works on dyeing speak of this circum-\nstantially. Suffice it to have alluded to pro-\ncesses by 'means of which the colour retains a\npermanency only to be destroyed with the sub-\nstance, and which may even increase in bright-\nness and beauty by use.\n\nXLIV.\n\nINTERMIXTURE, REAL.\n\nEvery intermixture pre-supposes a specific\nstate of colour ; and thus when we speak of in-\ntermixture, we here understand it in an atomic\n\n224 INTERMIXTURE, REAL.\n\nsense. We must first have before us certain\nbodies arrested at any given point of the colorific\ncircle, before we can produce gradations by ttieir\nunion.\n\nYellow, blue, and red, may be assumed as\npure elementary colours, already existing ; from\nthese, violet, orange, and green, are the simplest\ncombined results.\n\nSome persons have taken much pains to de*\nfine these intermixtures more accurately, by\nrelations of number, measure, and weight, but\nnothing very profitable has been thus accom-\nplished.\n\nPainting consists, strictly speaking, in the\nintermixture of such specific colouring bodies\nand their infinite possible combinations — com-\nbinations which can only be appreciated by the\nnicest, most practised eye, and only accom-\nplished under its influence.\n\nThe intimate combination of these ingredients\nis efiected, in the first instance, through the most\nperfect comminution of the material by means\nof grinding, washing, &c., as well as by vehicles\n\nINTERMIXTURE, REAL. 225\n\nor liquid mediums which hold together the pul-\nverized substance, and combine organically,\nas it were, the unorganic ; such are the oils,\nresins, &c. — Note V.\n\nIf all the colours are mixed together they re-\ntain their general character as o-xisp^v, and as\nthey are no longer seen next each other, no\ncompleteness, no harmon}^ is experienced ; the\nresult is grey, which, like apparent colour,\nalways appears somewhat darker than white,\nand somewhat lighter than black.\n\nThis grey may be produced in various ways.\nBy mixing yellow and blue to an emerald\ngreen, and then adding pure red, till all three\nneutralize each other ; or, by placing the primi-\ntive and intermediate colours next each other\nin a certain proportion, and afterwards mixing\nthem.\n\nIf\n\nThat ail the colours mixed together produce\nwhite, is an absurdity which people have credu-\nlously been accustomed to repeat for a century,\nin opposition to the evidence of their senses.\n\nColours when mixed together retain their\n\nQ\n\n226 INTERMIXTURE, REAL.\n\noriginal darkness. The darker the colours^ the\ndarker will be the grey resulting from their\nunion, till at last this grey approaches black.\nThe lighter the colours the lighter will be the\ngrey^ which at last approaches white4\n\nXLV.\n\nINTERMlXTURi; APPARENT.\n\nThe inter mixture, which is only apparent,\nnaturally invites our attention in connexion with\nthe foregoing ; it is in many respects important,\nand, indeed, the intermixture which we have\ndistinguished as real, might be considered as\nmerely apparent. For the elements of which\nthe combined colour consists are only too small\nto be considered as distinct parts. Yellow and\nblue powders mingled together appear green to\nthe naked eye, but through a magnifying glass\nwe can still perceive yellow and blue distinct\nirom each other. Thus yellow and blue stripes\nseen at a distance, present a green mass; the\nsame observation is applicable with regard to\nthe intermi3(ture of other specific colours.\n\nIn the description of our apparatus we shall\n\nIltTERHntTURB, APPARBKT. ]f37\n\nhare occasion to mention the wheel by means of\nwhich the apparent intermixture is produced\nby rapid movement. Various colours are ar-\nranged near each other round the edge of a\ndisk, which is made to revolve with velocity,\nand thus by having several such disks ready,\nevery possible intermixture can be presented to\nthe eye, as well as the mixture of all colours to\ngrey, darker or lighter, according to the depth\nof the tints as above explained.\n\nPhysiological colours admit, in like manner,\nof being mixed with others. If, for example,\nwe produce the blue shadow (65) on a light\nyellow paper, the surface will appear green.\nThe same happens with regard to the other\ncolours if the necessary prepcuutions are at-\ntended to.\n\nIf, when the eye is impressed with risionafy\nimages that last for a while, we look on coloured\nsurfaces, an intermixture also takes place ; the\nspectrum is determined to a new colour which\nis composed of the two.\n\nPhjrsical colours also admit of combination.\nHere might be adduced the experiments in\nQ 2\n\n228 INTERMIXTURE, APPARENT.\n\nwhich many-coloured images are seen through\nthe prism, as we have before shown in detail\n(258, 284).\n\nThose who have prosecuted these inquiries\nhave, however, paid most attention to the ap-\npearances which take place when the prismatic\ncolours are thrown on coloured surfaces.\n\nWhat is seen under these circumstances is\nquite simple. In the first place it must be re-\nmembered that the prismatic colours are much\nmore vivid than the colours of the surface on\nwhich they are thrown. Secondly, we have\nto consider that the prismatic colours may be\neither homogeneous or heterogeneous, with the\nrecipient surface. In the former case the sur-\nface deepens and enhances them, and is itself\nenhanced in return, as a coloured stone is\ndisplayed by a similarly coloured foil. In the\nopposite case each vitiates, disturbs, and des*\ntroys the other.\n\nThese experiments may be repeated with\ncoloured glasses, by causing the sun-light to\nshine through them on coloured surfaces. In\nevery instance similar results will appear.\n\n'«F\n\nINTERMIXTURE, APPARENT. 229\n\nThe same effect takes place when we look on\ncoloured objects through coloured glasses ; the\ncolours being thus according to the same con-\nditions enhanced, subdued, or neutralized.\n\nIf the prismatic colours are suffered to pass\nthrough coloured glasses, the appearances that\ntake place are perfectly analogous ; in these\ncases more or less force, more or less light and\ndark, the clearness and cleanness of the glass\nare all to be allowed for, as they produce many\ndelicate varieties of effect : these will not escape\nthe notice of every accurate observer who takes\nsufficient interest in the inquiry to go through\nthe experiments.\n\nIt is scarcely necessary to mention that\nseveral coloured glasses, as well as oiled or\ntransparent papers, placed over each other,\nmay be made to produce and exhibit every kind\nof intermixture at pleasure.\n\nLastly, the operation of glazing in painting\nbelongs to this kind of intermixture ; by this\nmeans a much more refined union may be pro-\nduced than that arising from the mechanical,\natomic mixture which is commonly employed.\n\nXLVI.\n\nCOMMUNICATION, ACTUAL;\n\nHaying now provided the colouring materials,\nas before shown, a further question arises how\nto communicate these to colourless substances :\nthe answer is of the greatest importance from\nthe connexion of the object with the ordinary\nwants of men^ with useful purposes^ and with\ncommercial and technical interests.\n\nHere, again, the dark quality of every colour\nagain comes into the account. From a yellow\nthat is very near to white« through orange, and\nthe hue of minium to pure red and carmine,\nthrough all gradations of violet to the deepest\nblue which is almost identified with black,\ncolour still increases in darkness. Blue once\ndefined, admits of being diluted, made light,\nunited with yellow, and then, as green, it ap-\nproaches the light side of the scale : but this is\nby no means according to its own nature.\n\nIn the physiological colours we have already\nseen that they are less than the light, inasmuch\n\nCOliMUNICATION, ACTUAL. 231\n\nas they are a repetition of an impression of\nlight, nay, at last they leave this impression\nquite as a dark. In physical experiments the\nemployment of semi-transparent mediums, the\neffect of semi-trdnsparent accessory images,\ntaught us that in such cases we have to do with\na subdued light, with a transition to darkness.\n\nIn treating of the chemical origin of pigments\nwe found that the same effect was produced on\nthe very first excitement. The yellow tinge\nwhich mantles over the steel, already darkens\nthe shining surface. In changing white lead to\nmassicot it is evident that the yellow is darker\nthan white.\n\nThis process is in the highest degree delicate {\nthe growing intenseness, as it still increases,\ntinges the substance more and more intimately\nand powerfully, and thus indicates the extreme\nfineness, and the infinite divisibility of the\ncoloured atoms.\n\nThe colours which approach the dark side,\nand consequently, blue in particular, can be\nmade to approximate to black ; in fact, a very\nperfect Prussian blue, or an indigo acted on by\nvitriolic acid appears almost as a black.\n\n232 COMMUNICATION, ACTUAL.\n\nA remarkable appearance may be here ad-\nverted to ; pigments, in their deepest and most\ncondensed state, especially those produced from\nthe vegetable kingdom, such as the indigo just\nmentioned, or madder carried to its intensest\nhue, no longer show their own colour ; on the\ncontrary, a decided metallic shine is seen on\ntheir surface, in which the physiological com-\npensatory colour appears.\n\nAll good indigo exhibits a copper-colour in its\nfracture, a circumstance attended to, as a known\ncharacteristic, in trade. Again, the indigo which\nhas been acted on by sulphuric acid, if thickly\nlaid on, or suflFered to dry so that neither white\npaper nor the porcelain can appear through,\nexhibits a colour approaching to orange.\n\nThe bright red Spanish rouge, probably pre-\npared from madder, exhibits on its surface a\nperfectly green, metallic shine. If this colour,\nor the blue before mentioned, is washed with a\npencil on porcelain or paper, it is seen in its\nreal state owing to the bright ground shining\nthrough.\n\nColoured liquids appear black when no light\n\nCOMMUNICATION, ACTUAL. 233\n\nis transmitted through them, as we may easily\nsee in cubic tin vessels with glass bottoms. In\nthese every transparent-coloured infusion will\nappear black and colourless if we place a black\nsurface under them.\n\nIf we contrive that the image of a flame be\nreflected from the bottom, the image will appear\ncoloured. If we lift up the vessel and suffer the\ntransmitted light to fall on white paper under it,\nthe colour of the liquid appears on the paper.\nEvery light ground seen through such a coloured\nmedium exhibits the colour of the medium.\n\nThus every colour, in order to be seen, must\nhave a light within or behind it. Hence the\nlighter and brighter the grounds are, the more\nbrilliant the colours appear. If we pass lac-\nvamish over a shining white metal surface, as\nthe so-called foils are prepared, the splendor of\nthe' colour is displayed by this internally re-\nflected light as powerfully as in any prismatic\nexperiment ; nay, the force of the physical co-\nlours is owing principally to the circumstance\n\nlat light is always acting with and behind\nth^\n\nLichtenberg, who of necessity followed the\n\n234 COMBfUNICATION, ACTVAJL.\n\nr^eived Uieory« owing to the time and circoiiD-\nstances in which he lived, was yet too good ao.\nobserver, and too acute not to explain and das*\nsify, after his fashion, what was evident to his\nsenses. He says, in the preface to Delaval, ** It\nappears to me also, on other grounds, probable,\nthat our organ, in order to be impressed by a\ncolour, must at the same time be impressed by\nall light (white)-\"\n\nTo procure white as a ground is the chief\nbusiness of the dyer. Every colour may be\neasily communicated to colourless earths, espe-\ncially to alum : but the dyer has especially to\ndo with animal and vegetable products as the\nground of his operations.\n\nEverything living tends to colour — to local,\nspecific colour, to effect, to opacity — pervading\nthe minutest atoms. Everything in which life\nis extinct approximates to white (494), to the\nabstract, the general state, to clearness,* to\ntransparence.\n\nHow this is put in practice in technical opera*\ntions remains to be adverted to in the chapter\non the privation of colour. With regard to the\n\n* VerkUurung, literally clarification.\n\nCOMMUNICATION; AFFABSNT. 2S6\n\ncommunication of colour, we have e(E^>ecially to\nbear in mind that animals and vegetables^ in a\nliving state, produce colours, and hence their\nsubstances, if deprived of colours, can the more\nreadily re-assume them.\n\nXLVII.\n\nCOMMUNICATION, APPARENT.\n\nThe communication of colours, real as well as\napparent, corresponds, as may easily be seen,\nwith their intermixture : we need not, therefore,\nrepeat what has been already sufficiently en-\ntered into.\n\nYet we may here point out more circumstan-^\ntially the importance of an apparent communi-\ncation which takes place by means of reflection.\nThis phenomenon is well known, but still it is\npregnant with inferences, and is of the greatest\nimportance both to the investigator of nature\nand to the painter.\n\nLet a surface coloured with any one of the\npositive colours be placed in the sun^ and let its\n\n236 COMMUM ICATION, APPARENT.\n\nreflection be thrown on other colourless objects.\nThis reflection is a kind of subdued light, a\nhalf-light, a half-shadow, which, in a subdued\nstate, reflects the colours in question.\n\nIf this reflection acts on light surfaces, it is\nso far overpowered that we can scarcely per-\nceive the colour which accompanies it ; but if it\nacts on shadowed portions, a sort of magical\nunion takes place with the (rxispo). Shadow is\nthe proper element of colour, and in this case\na subdued colour approaches it, lighting up,\ntinging, and enlivening it. And thus arises an\nappearance^ as powerful as agreeable, which\nmay render the most pleasing service to the\npainter who knows how to make use of it.\nThese are the types of the so-called reflexes,\nwhich were only noticed late in the history of\nart, and which have been too seldom employed\nin their full variety.\n\nThe schoolmen called these colours cohres na-\ntionales and intentionales, and the history of the\ndoctrine of colours will generally show that the\nold inquirers already observed the phenomena\nwell enough, and knew how to distinguish them\nproperly, although the whole method of treating\nsuch subjects is very diflerent from ours.\n\nXLVIII.\n\nEXTBACTION.\n\nColour may be extracted from substances,\nwhether they possess it naturally or by com-\nmunication, in various ways. We have thus the\npower to remove it intentionally for a useful\npurpose, but, on the other hand, it often files\ncontrary to our wish.\n\nNot only are the elementary earths in their\nnatural state white, but vegetable and animal\nsubstances can be reduced to a white state with-\nout disturbing their texture. A pure white is\nvery desirable for various uses, as in the instance\nof our preferring to use linen and cotton stufl^\nuncoloured. In like manner some silk stufis,\npaper, and other substances, are the more agree-\na.ble the whiter they can be. Again, the chief\nbasis of all dyeing consists in white grounds.\nFor these reasons manufacturers, aided by acci-\ndent and contrivance, have devoted themselves\nassiduously to discover means of extracting\ncolour: infinite experiments have been made\nin connexion with this object, and many im-t\nportant facts have been arrived at.\n\n238 EXTRACTION.\n\nIt is in accomplishing this entire extraction of\ncolour that the operation of bleaching consists,\nwhich is very generally practised empirically or\nmethodically. We will here shortly state the\nleading principles.\n\nLight is considered as one of the first means\nof extracting colour from substances, and not\n6nly the sun-light, but the mere powerless day-\nlight : for as both lights — the direct light of the\nsun, as well as the derived light of the sky —\nkindle Bologna phosphorus, so both act on co-\nloured surfaces. Whether the light attacks the\ncolour allied to it^ and, as it were, kindles and\nconsumes it, thus reducing the definite quality\nto a general state, or whether some other opera-\ntion, unknown to us, takes place, it is clear that\nlight exercises a great power on coloured sur-\nfaces, and bleaches them more or less. Here,\nhowever, the different colours exhibit a different\ndegree of durability ; yellow, especially if pre-\npared from certain materials, is, in this case,\nthe first to fly.\n\nNot only light, but air, and especially water,\nact strongly in destroying colour. It has been\neven asserted that thread, well soaked and\n\nBXTRACTION. 239\n\nspread oh the grass at night, bleaches better\nthan that which is exposed, after soaking, to the\nsun-light. Thus, in this case, water proves to\nbe a solving and conducting agent, removing the\naccidental quality, and restoring the substance\nto a general or colourless state.\n\nThe extraction of colour is also effected by\nre-*agents. Spirits of wine has a peculiar tend-\nency to attract the juice which tinges plants^\nftnd becomes coloured with it often in a very\npermanent manner. Sulphuric acid is very effi*\nqient in removing colour, especially from wool\nand silk, and every one is acquainted with the\nuse of sulphur vapours in bleaching.\n\nThe strongest acids have been recommended\nmore recently as more expeditious agents in\nbleaching.\n\nThe alkaline re-agents produce the same\neffects by contrary means — ^lixiviums alone, oils\nand fat combined with lixiviums to soap, and\nso forth.\n\nBefore we dismiss this subject, we observe\n\n240 EXTRACTION.\n\nthat it may be well worth while to make certain\ndelicate experiments as to how far light and air\nexhibit their action in the removal of colour. It\nmight be possible to expose coloured substances\nto the light under glass bells, without air^ or\nfilled with common or particular kinds of air.\nThe colours might be those of known fugacity,\nand it might be observed whether any of the\nvolatilized colour attached itself to the glass or\nwas otherwise perceptible as a deposit or preci*\npitate ; whether, again, in such a case, this ap-\npearance would be perfectly like that which had\ngradually ceased to be visible, or whether it had\nsuffered any change. Skilful experimentalists\nmight devise various contrivances with a view\nto such researches.\n\nHaving thus first considered the operations of\nnature as subservient to our purposes, we add a\nfew observations on the modes in which they\nact against us.\n\nThe art of painting is so circumstanced that\nthe most beautiful results of mind and labour are\naltered and destroyed in various ways by time*\nHence great pains have been always taken to\nfind durable pigments, and so to unite them\nwith each other and with their ground, that their\n\nEXTRACTION. 24 1\n\npermanency might be further insured. The\ntechnical history of the schools of painting\naffords sufficient information on this point.\n\n. We may here, too, mention a minor art, to\nwhich, in relation to dyeing, we are much in-\ndebted, namely, the weaving of tapestry. As\nthe manufacturers were enabled to imitate the\nmost delicate shades of pictures, and hence\noften brought the most variously coloured ma-\nterials together, it was soon observed that the\ncolours were not all equally durable, but that\nsome faded from the tapestry more quickly than\nothers. Hence the most diligent efforts were\nmade to ensure an equal permanency to all the\ncolours and their gradations. This object was\nespecially promoted in France, under Colbert,\nwhose regulations to this effect constitute an\nepoch in the history of dyeing. The gay dye\nwhich only aimed at a transient beauty, was\npractised by a particular guild. On the other\nhand, great pains were taken to define the\ntechnical processes which promised durability.\nAnd thus, after considering the artificial ex-\ntraction, the evanescence, and the perishable\nnature of brilliant appearances of colour, we\nare again returned to the desideratum of per-\nmanency.\n\nn\n\nXLIX.\n\nNOMENCLATURE.\n\nAfter what has been adduced respecting the\norigin, the increase, and the affinity of colours,\nwe may be better enabled to judge what nomen-\nclature would be desirable in future, and what\nmight be retained of that hitherto in use.\n\nThe nomenclature of colours, like all other\nmodes of designation, but especially those em-\nployed to distinguish the objects of sense, pro-\nceeded in the first instance from particular to\ngeneral, and from general back again to par-\nticular terms. The name of the species became\na generic name to which the individual was\nagain referred.\n\nThis method might have been followed in\nconsequence of the mutability and uncertainty\nof ancient modes of expression, especially since,\nin the early ages, more reliance may be sup-\nposed to have been placed on the vivid impres-\nsions of sense. The qualities of objects were\ndescribed indistinctly, because they were im-\npressed clearly on every imagination.\n\nNOMENCLATURB. 243\n\nThe pure chromatic circle was limited, it is\ntrae ; but, specific as it was» it appears to have\nbeen applied to innumerable objects, while it\nwas circumscribed by qualifying characteristics.\nIf we take a glance at the copiousness of the\nGreek and Roman terms, we shall perceive how\nmutable the words were, and how easily each\nwas adapted to almost every point in the colo-\nrific circle. — Note W.\n\nIn modern ages terms for many new grada-\ntions were introduced in consequence of the\nvarious operations of dyeing. Even the colours\nof fashion and their designations, represented ah\nendless series of specific hues. We shall, on occa-\nsion, em ploy the chromatic terminology of modern\nlanguages^ whence it will appear that the Bim\nhas gradually been to introduce more exact de-\nfinitions^ and to individualise and arrest a fixed\nand specific state by language equally distinct.\n\nWith regard to the German terminology, it\nhas the advantage of possessing four mono-\nsyllabic names no longer to be traced to their\norigin, viz., yellow (Gelb), blue, red, green.\nThey represent the most general idea of colour\nto the imagination, without reference to any very\nspecific modification.\n\nR 2\n\n244 NOMENCLATURE.\n\nIf we were to add two other qualifying terms\nto each of these four, as thus — red-yellow, and\nyellow-red, red-blue and blue-red, yellow-green\nand green-yellow, blue-green and green-blue,*\nwe should express the gradations of the chro->>\nmatic circle with sufficient distinctness ; and if\nwe were to add the designations of light and\ndark, and again define, in some measure, the\ndegree of purity or its opposite by the mono-\nsyllables black, white, grey, brown, we should\nhave a tolerably sufficient range of expressions\nto describe the ordinary appearances presented\nto us, without troubling ourselves whether they\nwere produced dynamically or atomically.\n\nThe specific and proper terms in use might,\nhowever, still be conveniently employed, and we\nhave thus made use of the words orange and\nviolet. We have in like manner employed the\nword ^^ purpur' to designate a pure central red,\nbecause the secretion of the murex or *^ purpura^\nis to be carried to the highest point of culmina-\ntion by the action of the sun-light on fine linen\nsaturated with the juice.\n\n* This description is suffered to remain because it accounts for\nthe terminology employed throughout. — T.\n\nL.\n\nMINERALS.\n\nThe colours of minerals are all of a chemical\nnature, and thus the modes in which they are\nproduced may be explained in a general way by\nwhat has been said on the subject of chemical\ncolours.\n\n614,\n\nAmong the external characteristics of mine-\nrals, the description of their colours occupies\nthe first place ; and great pains have been taken,\nin the spirit of modern times, to define and arrest\nevery such appearance exactly : by this means,\nhowever, new difficulties, it appears to us, have\nbeen created, which occasion no little incon-\nvenience in practice.\n\nIt is true, this precision, when we reflect how\nit arose, carries with it its own excuse. The\npainter has at all times been privileged in the\nuse of colours. The few specific hues, in them-\nselves, admitted of no change ; but from these,\ninnumerable gradations were artificially pro-\nduced which imitated the surface of natural\nobjects. It was, therefore, not to be wondered\n\n246 MINERALS.\n\nat that these gradations should also be adopted\nas criterions, and that the artist should be in-\nvited to produce tinted patterns with which the\nobjects of nature might be compared, and\naccording to which they were to receive their\ndesignations.\n\nBut, after all, the terminology of colours which\nhas been introduced in mineralogy, is open to\nmany objections. The terms, for instance, have\nnot been borrowed from the mineral kingdom,\nas was possible enough in most cases, but\nfrom all kinds of visible objects. Too many\nspecific terms have been adopted ; and in seek-\ning to establish new definitions by combining\nthese> the nomenclators have not reflected that\nthey thus altogether efiace the image from the\nimagination, and the idea from the understand*\ning. Lastly, these individual designations of\ncolours, employed to a certain extent as ele-\nmentary definitions, are not arranged in the best\nmanner as regards their respective derivation\nfrom each other : hence, the scholar must learn\nevery single designation, and impress an almost\nlifeless but positive language on his memory.\nThe fiirther consideration of this would be too\nforeign to our present subject*\n\n* These remarks have reference to the German mineralogical\nterminology. — ^T.\n\nLI.\n\nPLANTS.\n\nThe colours of organic bodies in general may be\nconsidered as a higher kind of chemical opera-\ntion, for which reason the ancients employed\nthe word concoction, ^H^^s^ to designate the\nprocess. All the elementary colours, as well as\nthe combined and secondary hues, appear on\nthe surface of organic productions, while on the\nother hand, the interior^ if not colourless, ap-\npears, strictly speaking, negative when brought\nto the light. As we propose to communicate\nour views respecting organic nature, to a certain\nextent, in another place, we only insert here\nwhat has been before connected with the doc-\ntrine of colours, while it may serve as an intro-\nduction to the further consideration of the views\nalluded to : and first, of plants.\n\nSeeds, bulbs, roots, and what is generally shut\nout from the light, or immediately surrounded\nby the earth, appear, for the most part, white.\n\nPlants reared from seed, in darkness, are\nwhite, or approaching to yellow. Light, on the\n\n248 PLANTS.\n\nother hand, in acting on their colours, acts at\nthe same time on their form.\n\nPlants which grow in darkness make, it is\ntrue, long shoots from joint to joint : but the\nstems between two joints are thus longer than\nthey should be; no side stems are produced,\nand the metamorphosis of the plant does not\ntake place.\n\nLight, on the other hand, places it at once in\nan active state ; the plant appears green, and\nthe course of the metamorphosis proceeds unin-\nterruptedly to the period of reproduction.\n\nWe know that the leaves of the stem are only\npreparations and pre-significations of the in-\nstruments of florification and fructification, and\naccordingly we can already see colours in the\nleaves of the stem which, as it were, announce\nthe flower from afar, as is the case in the ama-\nranthus.\n\nThere are white flowers whose petals have\nwrought or refined themselves to the greatest\npurity ; there are coloured ones, in which thg\n\nPLANTS. 249\n\nelementary hues may be said to fluctuate to and\nfro. There are some which, in tending to the\nhigher state, have only partially emancipated\nthemselves from the green of the plant.\n\nFlowers of the same genus, and even of the\nsame kind, are found of all colours. Roses, and\nparticularly mallows, for example, vary through\na great portion of the colorific circle from white\nto yellow, then through red-yellow to bright\nred, and from thence to the darkest hue it can\nexhibit as it approaches blue.\n\nOthers already begin from a higher degree\nin the scale, as, for example, the poppy, which\nis yellow-red in the first instance, and which\nafterwards approaches a violet hue.\n\nYet the same colours in species, varieties, and\neven in families and classes, if not constant, are\nstill predominant, especially the yellow colour :\nblue is throughout rarer.\n\nA process somewhat similar takes place in\nthe juicy capsule of the fruit, for it increases in\ncolour from the green, through the yellowish\n\n250 PLANTS.\n\nand yellow, up to the highest red, the colour of\nthe rmd thus indicating the degree of ripeness.\nSome are coloured all round, some only on the\nsunny side, in which last case the augmentation\nof the yellow into red,— the gradations crowd-\ning in and upon each other, — may be veiy well\nobserved.\n\nMany fruits, too, are coloured internally;\npure red juices, especially, are common.\n\nThe colour which is found superficially in the\nflower and penetratingly in the fruit, spreads\nitself through all the remaining parts, colouring\nthe roots and the juices of the stem, and this\nwith a very rich and powerful hue.\n\nSo, again, the colour of the wood passes from\nyellow through the different degrees of red up\nto pure red and on to brown. Blue woods are\nunknown to me ; and thus in this degree of or-\nganisation the active side exhibits itself power-\nfully, although both principles appear balanced\nin the general green of the plant.\n\nWe have seen above that the germ pushing\n\nPLANTS. 251\n\nfrom the earth is generally white and yellowish,\nbut that by means of the action of light and air\nit acquires a green colour. The same happens\nwith young leaves of trees, as may be seen, for\nexample, in the birch, the young leaves of which\nare yellowish, and if boiled, yield a beautiful\nyellow juice : afterwards they become greener,\nwhile the leaves of other trees become gradually\nblue-green.\n\nThus a yellow ingredient appears to belong\nmore essentially to leaves than a blue one ; for\nthis last vanishes in the autumn, and the yellow\nof the leaf appears changed to a brown colour.\nStill more remarkable, however, are the parti-\ncular cases where leaves in autumn again be-\ncome pure yellow, and others increase to the\nbrightest red.\n\nOther plants, again, may, by artificial treat-\nment be entirely converted to a colouring\nmatter, which is as fine, active, and infinitely\ndivisible as any other. Indigo and madder,\nwith which so much is effected, are examples :\nlichens are also used for dyes.\n\nTo this fact another stands immediately op-\n\n252 WORMS, INSECTS, FISHES.\n\nposed; we can, namely, extract the colouring\npart of plants, and, as it were, exhibit it apart,\nwhile the organisation does not on this account\nappear to suffer at all. The colours of flowers\nmay be extracted by spirits of wine, and tinge\nit ; the petals meanwhile becoming white.\n\nThere are various modes of acting on flowers\nand their juices by re-agents. This has been\ndone by Boyle in many experiments. Roses\nare bleached by sulphur, and may be restored\nto their first state by other acids; roses are\nturned green by the smoke of tobacco.\n\nLII.\n\nWORMS, INSECTS, FISHES.\n\nWith regard to creatures belonging to the lower\ndegrees of organisation, we may first observe\nthat worms, which live in the earth and remain\nin darkness and cold moisture, are imperfectly\nnegatively coloured ; worms bred in warm mois-\nture and darkness are colourless; light seems\nexpressly necessary to the definite exhibition of\ncolour.\n\nWORMS, INSECTS, FISHES. 253\n\nCreatures which live in water, which, although\na very dense medium, suffers sufficient light\nto pass through it, appear more or less coloured.\nZoophytes, which appear to animate the purest\ncalcareous earth, are mostly white ; yet we find\ncorals deepened into the most beautiful yellow-\nred : in other cells of worms this colour increases\nnearly to bright red.\n\nThe shells of the crustaceous tribe are beauti-\nfully designed and coloured, yet it is to be re-\nmarked that neither land-snails nor the shells\nof Crustacea of fresh water, are adorned with\nsuch bright colours as those of the sea.\n\nIn examining shells, particularly such as are\nspiral, we find that a series of animal organs,\nsimilar to each other, must have moved in-\ncreasingly forward, and in turning on an axis\nproduced the shell in a series of chambers, divi-\nsions, tubes, and prominences, according to a\nplan for ever growing larger. We remark, how-\never, tliat a tinging juice must have accompanied\nthe development of these organs, a juice which\nmarked the surface of the shell, probably through\nthe immediate co-operation of the sea-water,\nwith coloured lines, points, spots, and shadings :\n\n254 WORMS, INSECTS, FI8HX8.\n\nthis must have taken place at regular intervals,\nand thus left the indications of increasing growth\nlastingly on the exterior ; meanwhile the inte-\nrior is generally found white or only faintly co-\nloured.\n\nThat such a juice is to be found in shell -fish\nis, besides, sufficiently proved by experience; for\nthe creatures furnish it in its liquid and colour-\ning state: the juice of the ink-fish is an ex-\nample. But a much stronger is exhibited in the\nred juice found in many shell -fish, which\nwas so famous in ancient times, and has been\nemployed with advantage by the moderns.\nThere is, it appears, in the entrails of many of\nthe crustaceous tribe a certain vessel which is\nfilled with a red juice; this contains a very\nstrong and durable colouring substance, so much\nso that the entire creature may be crushed and\nboiled, and yet out of this broth a sufficiently\nstrong tinging liquid may be extracted. But\nthe little vessel filled with colour may be sepa-\nrated fi*om the animal, by which means of course\na concentrated juice is gained.\n\nThis juice has the property that when ex-\nposed to light and air it appears first yellowish,\nthen greenish ; it then passes to blue, then to a\n\nWORMS, INSECTS, FISHES. 255\n\nviolet, gradually growing redder ; and lastly, by\nthe action of the sun, and especially if trans-\nferred to cambric, it assumes a pure bright red\ncolour.\n\nThus we should here have an augmentation,\neven to culmination, on the minus side, which\nwe cannot easily meet with in inorganic cases ;\nindeed, we might almost call this example a\npassage through the whole scale, and we are\npersuaded that by due experiments the entire\nrevolution of the circle might really be effected,\nfor there is no doubt that by acids duly em-\nployed, the pure red may be pushed beyond the\nculminating point towards scarlet.\n\nThis juice appears on the one hand to be con-\nnected with the phenomena of reproduction,\neggs being found, the embryos of future shell-\nfish, which contain a similar colouring principle.\nOn the other hand, in animals ranking higher\nin the scale of being, the secretion appears to\nbear some relation to the development of the\nblood. The blood exhibits similar properties in\nregard to colour ; in its thinnest state it appears\nyellow; thickened, as it is found in the veins,\nit appears red ; while the arterial blood exhibits\na brighter red, probably owing to the oxydation\n\n250 WORMS, INSECTS, FISHES.\n\nwhich takes place by means of breathing. The\nvenous blood approaches more to violet, and by\nthis mutability denotes the tendency to that\naugmentation and progression which are now\nfamiliar to us.\n\nBefore we quit the element whence we de-\nrived the foregoing examples, we may add a few\nobservations on fishes, whose scaly surface is\ncoloured either altogether in stripes, or in spots,\nand still oftener exhibits a certain iridescent\nappearance, indicating the affinity of the scales\nwith the coats of shell-fish, mother-of-pearl, and\neven the pearl itself. At the same time it\nshould not be forgotten that warmer climates,\nthe influence of which extends to the watery\nregions, produce, embellish, and enhance these\ncolours in fishes in a still greater degree.\n\nIn Otaheite, Forster observed fishes with\nbeautifully iridescent surfaces, and this effect\nwas especially apparent at the moment when\nthe fish died. We may here call to mind the\nhues of the chameleon, and other similar ap-\npearances ; for when similar facts are presented\ntogether, we are better enabled to trace them.\n\nLastly » although not strictly in the same\n\nr-^\n\nWORMS, INSECTS, FISHES. 257\n\nclass, the iridescent appearance of certain mo-\nluscae may be mentioned, as well as the phos-\nphorescence which, in some marine creatures^\nit is said becomes iridescent just before it\nvanishes.\n\n•\n\nWe now turn our attention to those creatures\nwhich belong to light, air and dry warmth, and\nit is here that we tirst find ourselves in the\nliving region of colours. Here, in exquisitely\norganised parts, the elementary colours present\nthemselves in their greatest purity and beauty.\nThey indicate, however, that the creatures they\nadorn, are still low in the scale of organis-\nation, precisely because these colours can thus\nappear, as it were, unwrought. Here,, too,\nheat seems to contribute much to their develop-\nment.\n\nWe find insects which may be considered\naltogether as concentrated colouring matter;\namong these, the cochineals especially are cele-\nbrated ; with regard to these we observe that\ntheir mode of settling on vegetables, and even\nnestling in them, at the same time produces\nthose excrescences which are so useful as mor-\ndants in fixing colours.\n\ns\n\n258 WORMS, IN8BCTS, FISHES.\n\nBut the power of colour, accompanied by\nregular organisation, exhibits itself in the most\nstriking manner in those insects which require\na perfect metamorphosis for their development\n— in scarabaei, and especially in butterflies.\n\nThese last, which might be called true pro-\nductions of light and air, often exhibit the most\nbeautiful colours, even in their chrysalis state,\nindicating the future colours of the butterfly ; a\nconsideration which, if pursued further hereafter,\nmust undoubtedly afibrd a satisfactory insight\ninto many a secret of organised being.\n\nIf, again, we examine the wings of the but-\nterfly more accurately, and in its net-like web\ndiscover the rudiments of an arm, and observe\nfurther the mode in which this, as it were, flat-\ntened arm is covered with tender plumage and\nconstituted an organ of flying ; we believe we\nrecognise a law according to which the great\nvariety of tints is regulated. This will be a\nsubject for further investigation hereafter.\n\nThat, again, heat generally has an influence\n\nBIRDS. 259\n\non the size of the creature, on the accomplish*\nment of the form, and on the greater beauty of\nthe colours, hardly needs to be remarked.\n\nLIII.\n\nBIRDS.\n\nThe more we approach the higher organisations,\nthe more it becomes necessary to limit ourselves\nto a few passing observations ; for all the natural\nconditions of such organised beings are the re-\nsult of so many premises, that, without having\nat least hinted at these, our remarks would only\nappear daring, and at the same time insufficient.\n\nWe find in plants, that the consummate\nflower and fruit are, as it were, rooted in the\nstem, and that they are nourished by more per-\nfect juices than the original roots first afforded ;\nwe remark, too, that parasitical plants which\nderive their support from organised structures,\nexhibit themselves especially endowed as to\ntheir energies and qualities. We might in some\nsense compare the feathers of birds with plants\nof this description ; the feathers spring up as a\nlast structural result from the surface of a body\n\ns2\n\n260 BIRDS.\n\nwhich has yet much in reserve for the comple-\ntion of the external economy, and thus are very\nrichly endowed organs.\n\nThe quills not only grow proportionally to a\nconsiderable size, but are throughout branched,\nby which means they properly become feathers,\nand many of these feathered branches are again\nsubdivided ; thus, again, recalling the structure\nof plants.\n\nThe feathers are very different in shape and\nsize, but each still remains the same organ,\nforming and transforming itself according to\nthe constitution of the part of the body from\nwhich it springs.\n\nWith the form, the colour also becomes\nchanged, and a certain law regulates the general\norder of hues as well as that particular dis-\ntribution by which a single feather becomes\nparty coloured. It is from this that all com-\nbination of variegated plumage arises^ and\nwhence, at last, the eyes in the peacock's tail\nare produced. It is a result similar to that which\nwe have already unfolded in treating of the\nmetamorphosis of plants, and which we shall\ntake an early opportunity to prove.\n\nBIRDS. 261\n\nAlthough time and circumstances compel us\nhere to pass by this organic law, yet we are\nbound to refer to the chemical operations which\ncommonly exhibit themselves in the tinting of\nfeathers in a mode now sufficiently known to us.\n\nPlumage is of all colours, yet, on the whole,\nyellow deepening to red is commoner than blue.\n\nThe operation of light on the feathers and\ntheir colours, is to be remarked in all cases.\nThus, for example, the feathers on the breast of\ncertain parrots, are strictly yellow ; the scale-\nlike anterior portion, which is acted on by the\nlight, is deepened from yellow to red. The\nbreast of such a bird appears bright-red, but if\nwe blow into the feathers the yellow appears.\n\nThe exposed portion of the feathers is in all\ncases very different from that which, in a\nquiet state, is covered ; it is only the exposed\nportion, for instance, in ravens, which exhibits\nthe iridescent appearance ; the covered portion\ndoes not : from which indication, the feathers of\nthe tail when ruffled together, may be at once\nplaced in the natural order again.\n\nLIV.\n\nMAMMALIA AND HUMAN BEINGS.\n\nHere the elementary colours begin to leave us\naltogether. We are arrived at the highest de-\ngree of the scale, and shall not dwell on its\ncharacteristics long.\n\nAn animal of this class is distinguished\namong the examples of organised being. Every\nthing that exhibits itself about him is living.\nOf the internal structure we do not speak, but\nconfine ourselves briefly to the surface. The\nhairs are already distinguished from feathers,\ninasmuch as they belong more to the skin, in-\nasmuch as they are simple, thread-like, not\nbranched. They are however, like feathers,\nshorter, longer, softer, and firmer, colourless\nor coloured, and all this in conformity to laws\nwhich might be defined.\n\nWhite and black, yellow, yellow-red and\nbrown, alternate in various modifications, but\nthey never appear in such a state as to remind\nus of the elementary hues. On the contrary.\n\nMAMMALIA AND HUMAN BEINGS. 203\n\nthey are all broken colours subdued by organic\nconcoction, and thus denote, more or less, the\nperfection of life in the being they belong to.\n\nOne of the most important considerations con-\nnected with morphology, so far as it relates to\nsurfaces, is this, that even in quadrupeds the\nspots of the skin have a relation with the parts\nunderneath them. Capriciously as nature here\nappears, on a hasty examination, to operate, she\nnevertheless consistently observes a secret law.\nThe development and application of this, it is\ntrue, are reserved only for accurate and careful\ninvestigation and sincere co-operation.\n\nIf in some animals portions appear variegated\nwith positive colours, this of itself shows how\nfar such creatures are removed from a perfect\noi^nisation ; for, it may be said, the nobler a\ncreature is, the more all the mere material of\nwhich he is composed, is disguised by being\nwrought together ; the more essentially his sur-\nface corresponds with the internal organisation,\nthe less can it exhibit the elementary colours.\nWhere all tends to make up a perfect whole,\nany detached specific developments cannot talce\n\nplace.\n\nOf man we have little to say, for he is en-\n\n\\\n\n264 MAMMALIA AND HUMAN BEINGS.\n\ntirely distinct from the general physiological\nresults of which we now treat. So much in this\ncase is in affinity with the internal structure,\nthat the surface can only be sparingly endowed,\n\nWhen we consider that brutes are rather en-\ncumbered than advantageously provided with\nintercutaneous muscles ; when we see that\nmuch that is superfluous tends to the surface,\nas, for instance, large ears and tails^ as well as\nhair, manes, tufts ; we see that nature, in such\ncases, had much to give away and to lavish.\n\nOn the contrary, the general surface of the\nhuman form is smooth and clean, and thus in\nthe most perfect examples the beautiful forms\nare apparent ; for it may be remarked in pass-\ning, that a superfluity of hair on the chest, arms,\nand lower limbs, rather indicates weakness than\nstrength. Poets only have sometimes been in-\nduced, probably by the example of the ferine\nnature, so strong in other respects, to extol\nsimilar attributes in their rough heroes.\n\nBut we have here chiefly to speak of colour,\nand observe that the colour of the human skin,\nin all its varieties, is never an elementary co-\n\nKr\n\nMAMMALIA AND HUMAN BEINGS. 265\n\nlour, but presents^ by means of organic concoc*\ntion, a highly complicated result. — Note X.\n\nThat the colour of the skin and hair has rela-\ntion with the differences of character, is beyond\nquestion ; and we are led to conjecture that the\ncircumstance of one or other organic system\npredominating^ produces the varieties we see.\nA similar hypothesis may be applied to natrbns,\nin which case it might perhaps be observed, that\ncertain colours correspond with certain confirm-\nations, which has always been observed of the\nnegro physiognomy.\n\nLastly, we might here consider the problem-\natical question, whether all human forms and\nhues are not equally beautiful, and whether\ncustom and self-conceit are not the causes why\none is preferred to another ? We venture, how-\never, after what has been adduced, to assert that\nthe white man, that is, he whose surface varies\nfrom white to reddish, yellowish, brownish, in\nshort, whose surface appears most neutral in\nhue and least inclines to any particular or\npositive colour, is the most beautiful. On the\nsame principle a similar point of perfection in\nhuman conformation may be defined hereafter,\nwhen the question relates to form. We do not\n\n286 PHYSICAL AND CHEMICAL EFFECTS OF\n\nimagine that this long-disputed question is to be\nthus, once for all, settled, for there are persons\nenough who have reason to leave this significancy\nof the exterior in doubt ; but we thus express a\nconclusion^ derived from observation and reflec-\ntion, such as might suggest itself to a mind\naiming at a satisfactory decision. We subjoin\na few observations connected with the elemen-\ntary chemical doctrine of colours. — Note Y.\n\nLV.\n\nPHYSICAL AND CHEMICAL EFFECTS OF THE TRANSMIS-\nSION OF LIGHT THEOUGH COLOURED MEDIUMS.\n\nThe physical and chemical effects of colourless\nlight are known, so that it is unnecessary here\nto describe them at length. Ck>lourless light\nexhibits itself under various conditions as ex-\nciting warmth, as imparting a luminous quality\nto certain bodies, as promoting oxydation and\nde-oxydation. In the modes and degrees of\nthese effects many varieties take place, but no\ndifference is found indicating a principle of\ncontrast such as we find in the transmission of\ncoloured light. We proceed briefly to advert to\nthis.\n\nLIGHT THROUGH COLOURED MEDIUMS. 267\n\nLet the temperature of a dark room be ob-\nserved by means of a very sensible air-thermo-\nmeter; if the bulb is then brought to the direct\nsun light as it shines into, the room, nothing is\nmore natural than that the fluid should indicate\na much higher degree of warmth. If upon this\nwe interpose coloured glasses, it follows again\nquite naturally that the degree of warmth must\nbe lowered ; first, because the operation of the\ndirect light is already somewhat impeded by\nthe glass, and again, more especially, because a\ncoloured glass, as a dark medium, admits less\nlight through it.\n\nBut here a difference in the excitation of j\nwarmth exhibits itself to the attentive observer, \\\naccording to the colour of the glass. The yel-\nlow and the yellow-red glasses produce a higher\ntemperature than the blue and blue-red, the\ndifference being considerable.\n\nThis experiment may be made with the pris*\nmatic spectrum. The temperature of the room\nbeing first remarked on the thermometer, the\nblue coloured light is made to fall on the bulb,\nwhen a somewhat higher degree of warmth is\nexhibited, which still increases as the other co*\n\n268 PHYSICAL AND CHEMICAL EFFECTS OF\n\nlours are gradually brought to act on the mer-\ncury. If the experiment is made with the water-\nprism, so that the white light can be retained in\nthe centre, this, refracted indeed, but not yet co-\nloured light, is the warmest ; the other colours,\nstand in relation to each other as before.\n\nAs we here merely describe, without under-\ntaking to deduce or explain this phenomenon,\nwe only remark in passing, that the pure light is\nby no means abruptly and entirely at an end\nwith the red division in the spectrum, but that\na refracted light is still to be observed deviating\nfrom its course and, as it were, insinuating itself\nbeyond the prismatic image, so that on closer\nexamination it will hardly be found necessary\nto take refuge in invisible rays and their refrac-\ntion.\n\nThe communication of light by means of co-\nloured mediums exhibits the same difference.\nThe light communicates itself to Bologna phos-\nphorus through blue and violet glasses, but by\nno means through yellow and yellow-red glasses.\nIt has been even remarked that the phosphori\nwhich have been rendered himinous under violet\nand blue glasses, become sooner extinguished\nwhen afterwards placed under yellow and yel-\nlow-red glasses than those which have been\n\nLIGHT THROUGH COLOURED MEDIUMS. 269.\n\nsuffered to remain in a dark room without any\nfurther influence.\n\nThese experiments, like the foregoing, may\nalso be made by means of the prismatic spec-\ntrum, when the same results take place.\n\nTo ascertain the effect of coloured light on\noxydation and de-oxydation, the following means\nmay be employed : — Let moist, perfectly white\nmuriate of silver* be spread on a strip of paper;\nplace it in the light, so that it may become to a\ncertain degree grey, and then cut it in three\nportions. Of these, one may be preserved in a\nbook, as a specimen of this state ; let another\nbe placed under a yellow-red, and the third\nunder a blue-red glaas. The last will become a\ndarker grey, and exhibit a de-oxydation ; the\nother, under the yellow-red glass, will, on the\ncontrary, become a lighter grey, and thus ap-\nproach nearer to the original state of more per-\nfect oxydation. The change in both may.be\nascertained by a comparison with the unaltered\nspecimen.\n\nAn excellent apparjatus has been contrived to\n\n* Now generally called chloride of silver: the term in the\noriginal is Homailber. — T.\n\n270 CHEiaCAL EFFECT IN\n\nperform these experimente with the prismatic\nimage. The results are analogous to those al-\nready mentioned, and we shall hereafter give\nthe particulars, making use of the labours of an\naccurate observer, who has been for some time\ncarefully prosecuting these experiments*\n\nLVI.\n\nCHEMICAL EFFECT IN DIOPTRICAL ACHROMATISM.\n\nWe first invite our readers to turn to what has\nbeen before observed on this subject (285, 298),\nto avoid unnecessary repetition here. .\n\nWe can thus give a glass the property of\nproducing much wider coloured edges without\nrefracting more strongly than before^ that is,\nwithout displacing the object much more per-\nceptibly.\n\nThis property is communicated to the glass\nby means of metallic oxydes. Minium, melted\nand thoroughly united with a pure glass, pro-\n\n* The individual alluded to was Seebeck : the result of his ex\nperiments was published in the second volume. — T.\n\nDIOPTRICAL ACHB0HATI8M. 27 1\n\nduces this effect, and thus flint-glass (291) is\nprepared with oxyde of lead. Experiments of\nthis kind have been carried farther, and the so-\ncalled butter of antimony^ which, according to\na new preparation, may be exhibited as a pure\nfluid, has been made use of in hollow lenses\nand prisms, producing a very strong appearance\nof colour with a very moderate refraction, and\npresenting the effect which we have called hy-\nperchromatism in a very vivid manner.\n\nIn common glass, the alkaline nature ob-\nviously preponderates, since it is chiefly com-\nposed of sand and alkaline salts ; hence a series\nof experiments, exhibiting the relation of per-\nfectly alkaline fluids to perfect acids, might lead\nto useful results.\n\nFor, could the maximum and minimum be\nfound, it would be a question whether a refract-\ning medium could not be discovered, in which\nthe increasing and diminishing appearance of\ncolour, (an effect almost independent of refrac-\ntion,) could not be done away with altogether,\nwhile the displacement of the object would be\nunaltered.\n\nHow desirable, therefore, it would be with\n\n27S GENEBAL BEFLECTIONS.\n\nr^;ard to this last point, as well as for the el\ncidatioQ of the whole of this third division\nour work, and, indeed, for the elucidation of t\ndoctrine of colours generally, that those who e\noccupied in chemical researches, with new vie\never opening to them, should take this subjf\nin hand, pursuing into more delicate combio\ntions what we have only roughly hinted at, aj\nprosecuting their inquiries with reference\nscience as a whole.\n\n'\"^\n\nPART IV.\n\nGENERAL CHARACTERISTICS.\n\nWe have hitherto, in a manner forcibly, kept\nphenomena asunder, which, partly from their\nnature, partly in accordance with our mental\nhabits, have, as it were, constantly sought to be\nreunited. We have exhibited them in three\ndivisions. We have considered colours, first, as\ntransient, the result of an action and re-action\nin the eye itself; next, as passing efiects of\ncolourless, light-transmitting, transparent, or\nopaque mediums on light; especially on the\nluminous image ; lastly, we arrived at the point\nwhere we could securely pronounce them as\npermanent, and actually inherent in bodies.\n\nIn following this order we have as far as pos-\nsible endeavoured to define, to separate, and to\nclass the appearances. But now that we need\nno longer be apprehensive of mixing or con-*\nfounding them, we may proceed, first, to state\nthe general nature of these appearances con-\nsidered abstractedly, as an independent circle\nof facts, and, in the next place, to show how\nthis particular circle is connected with other\nclasses of analogous phenomena in nature.\n\nT\n\nTHE FACILITY WITH WHICH COLOUR APPEARS.\n\nWe have observed that colour under many\nconditions appears very easily. The suscep-\ntibility of the eye with regard to light, the\nconstant re-action of the retina against it, pro-\nduce instantaneously a slight iridescence.\nEvery subdued light may be considered as\ncoloured, nay, we ought to call any light coloured^\ninasmuch as it is seen. Colourless light, colour-\nless surfaces, are, in some sort, abstract ideas ;\nin actual experience we can hardly be said to \\)e\naware of them. — Note Z.\n\nIf light impinges on a colourless body, is re-\nflected from it or passes through it, colour im-\nmediately appears ; but it is necessary here to\nremember what has been so often urged by us,\nnamely, that the leading conditions of refrac-\ntion, reflection, &c., are not of themselves suffi-\ncient to produce the appearance. Sometimes,\nit is true^ light acts with these merely as light,\nbut oftener as a defined, circumscribed appear-\nance, as a luminous image. The semi-opacity\nof the medium is often a necessary condition ;\nwhile half, and double shadows, are required\nfor many coloured appearances. In all cases,\nhowever, colour appears instantaneously. We\nfind, again, that by means of pressure, breathing\nheat {432, 471), by various kinds of motion and\n\nTHE FORCE OP COLOtlB. 275\n\nalteration on smooth clean sarfaces (461), as\nwell as on colourless fluids (470), colour is im-\nmediately produced.\n\nThe slightest change has only to take place\nin the component parts of bodies, whether by\nimmixture with other particles or other such\neffects, and colour either makes its appearance\nor becomes changed.\n\nTHE FOECE OF COLOUR.\n\nThe physical colours, and especially those of\nthe prism, were formerly called \" colores em-\nphatici,\" on account of their extraordinary\nbeauty and force. Strictly speaking, however,\na high degree of effect may be ascribed to all\nappearances of colour, assuming that they are\nexhibited under the purest and most perfect\nconditions.\n\nThe dark nature of colour, its iull rich quality,\nis what produces the grave, and at the same\ntime fascinating impression we sometimes ex-\nperience, and as colour is to be considered a\ncondition of light, so it cannot dispense with\nlight as the co-operating cause of its appear-\nance, as its basis or ground ; as a power thus\ndisplaying and manifesting colour.\n\nT 2\n\nTHE DEFINITE NATURE OF COLOUR.\n\nThe existence and the relatively definite cha-\nracter of colour are one and the same thing.\nLight displays itself and the face of nature, as\nit were, with a general indifference, informiug\nus as to surrounding objects perhaps devoid of\ninterest or importance ; but colour is at all times\nspecific, characteristic, significant.\n\nConsidered in a general point of view, colour\nis determined towards one of two sides. It thus\npresents a contrast which we call a polarity,\nand which we may fitly designate by the ex-\npressions plus and minus.\n\nPlus. Minus.\n\nYellow. Blue.\n\nAction . Negation .*\n\nLight. Shadow.\n\nBrightness. Darkness.\n\nForce. Weakness.\n\nWarmth. Coldness.\n\nProximity. Distance.\n\nRepulsion Attraction.\n\nAffinity with acids Affinity with alkalis.\n\n* Wirkung, Beraubung; the last would be more literally ren-\n\ndered privation. The author has already frequently made use of\n\nm^ the tenns active and passive as equivalent to pltLS and mtnttr. — ^T.\n\nCOMBINATION OF THE TWO PRINCIPLES.\n\nIf these specific, contrasted principles are\ncombined, the respective qualities do not there-\nfore destroy each other: for if in this intermix-\nture the ingredients are so perfectly balanced that\nneither is to be distinctly recognised, the union\nagain acquires a specific character ; it appears\nas a quality by itself in which we no longer\nthink of combination. This union we call green.\n\nThus, if two opposite phenomena springing\nfrom the same source do not destroy each other\nwhen combined, but in their union present a\nthird appreciable and pleasing appearance, this\nresult at once indicates their harmonious rela-\ntion. The more perfect result yet remains to be\nadverted to.\n\nAUGMENTATION TO BED.\n\nBlue and yellow do not admit of increased\nintensity without presently exhibiting a new\nappearance in addition to their own. Each\ncolour, in its lightest state, is a dark ; if con-\ndensed it must become darker, but this effect no\nsooner takes place than the hue assumes an\nappearance which we designate by the word\nreddish.\n\n278 AUGMENTATION TO EED.\n\nThis appearance still increases, so that when\nthe highest degree of intensity is attained it\npredominates over the original hue. A powerful\nimpression of light leaves the sensation of red\non the retina. In the prismatic yellow-red\nwhich springs directly from the yellow, we\nhardly recognise the yellow.\n\nThis deepening takes place again by means of\ncolourless semi-transparent mediums, and here\nwe see the effect in its utmost purity and ex-\ntent. Transparent fluids, coloured with any\ngiven hues, in a series of glass- vessels, exhibit\nit very strikingly. The augmentation is unre-\nmittingly rapid and constant; it is universal,\nand obtains in physiological as well as in phy-\nsical and chemical colours.\n\nJUNCTION OF THE TWO AUGMENTED EXTREMES.\n\nAs the extremes of the simple contrast pro-\nduce a beautiful and agreeable appearance by\ntheir union, so the deepened extremes on being\nunited, will present a still more fascinating\ncolour ; indeed, it might naturally be expected\nthat we should here find the acme of the wiiole\nphenomenon.\n\nCOKPLBTEHBSS THE RESULT OF TAKIETY. 279\n\nAnd such is the fact, for p^ire red appears ; a\ncolour to which, from its excellence, we have\nappropriated the term \" purpur.\"\"\n\nThere are Tarious modes in which pure red\nmay appear. By bringing together the violet\nedge and yellow-red border in prismatic experi-\nments, by continued augmentation in chemical\noperations, and by the oi^anic contrast in phy-\n.siological effects.\n\nAs a pigment it cannot be produced by inter-\nmixture or union, but only by arresting the hue\nin substances cfaemically acted on, at the high\nculminating point. Hence the painter is jus-\ntified in assuming that there are three primitive\ncolours from which he combines all the others.\nThe natural philosopher, on the other hand,\nassumes only two elementary colours, from which\nhe, in like manner, developed and combines the\nrest.\n\nCOUPLBTENBSS THE EE80LT OF TABIBTY IN OOLOUK.\n\nThe various appearances of colour arrested in\n\n* Wherever this vord occun incidentally it is translated fnire\nred, the English word purple being generally employed to denote\na colour similar to violet. — T.\n\n382 PEKMAN»^OE OF COLOUE.\n\nto the rapid excitation and definition of colour,\nimmixture!', augmentation, combination, separa-\ntion, not forgetting the law of compensatory\nharmony, all takes place with the greatest\nrapidity and facility ; but with equal quickness\ncolour again alt(^ether disappears.\n\nThe physiological appearances are in no wise\nto be arrested ; the physical last only as long as\nthe external condition lasts ; even the chemical\ncolours have great mutability, they may be\nmade to pass and repass horn one side to the\nother by means of opposite re-agents, and may\neven be annihilated altogether.\n\nPERMANENCE OF COLOUR.\n\nThe chemical colours aiford evidence of very\ngreat duration. Colours fixed in glass by\nfusion, and by nature in gems, defy all time and\nre-action.\n\nThe art of dyeing again fixes colour very\npowerfully. The hues of pigments which might\notherwise be easily rendered mutable by re-\nagents, may be communicated to substances in\nthe greatest permanency by means of mordants.\n\nPART V.\n\nRELATION TO OTHER PURSUITS— RELATION TO\n\nFHILOSOPHY.\n\nThe inyestigator of nature cannot be required\nto be a philosopher, but it is expected that he\nshould so far have attained the habit of philo-\nsophizing, as to distinguish himself essentially\nfrom the world, in order to associate himself\nwith it again in a higher sense. He should\nform to himself a method in accordance with\nobservation, but he should take heed not to re-\nduce observation to mere notion, to substitute\nwords for this notion, and to use and deal with\nthese words as if they were things. He should\nbe acquainted with the labours of philosophers*\nin order to follow up the phenomena which have\nbeen the subject of his observation, into the\nphilosophic region.\n\nIt cannot be required that the philosopher\nshould be a naturalist, and yet his co-operation\nin physical researches is as necessary as it is\ndesirable. He needs not an acquaintance with\ndetails for this, but only a clear view of those\nconclusions where insulated facts meet.\n\n286 BBLATION TO IfATHBMATICS.\n\ntion, as well as in the polemical and historical\nportions of his work ; for he will have to return\nto the consideration of this point hereafter, on\nan occasion where it will be necessary to speak\nwith less reserre.\n\nRELATION TO MATHEMATICS.\n\nIt may be expected that the investigator of\nnature, who proposes to treat the science of\nnatural philosophy in its entire range, should\nbe a mathematician. In the middle ages, ma-\nthematics was the chief organ by means of\nwhich men hoped to master the secrets of nature,\nand even now, geometry in certain departments\nof physics, is justly considered of first import-\nance.\n\nThe author can boast of no attainments of\nthis kind, and on this account confines himself\nto departments of science which are indepen-\ndent of geometry; departments which in mo-\ndem times have been opened up far and wide.\n\nIt will be universally allowed that mathemar\ntics, one of the noblest auxiliaries which can\nbe employed by man, has, in one point of view,\nbeen of the greatest use to the physical sciences;\nbut that, by a false application of its methods,\n\naSULTlON TO MATUBMATICS. 287\n\nit 1ul8, in ma^y respects, been prejudicial to-\nthem, is also not to be deoied; we find it here\nand there reluctantly admitted.\n\nThe theory of colours, in particular, has suf-\nfered much, and its progress has been incalcu-\nlably retarded by having been mixed up with^\noptics generally, a science which cannot dis-\npense jvith matheraatica ; whereas the theory of\ncolours, in strictness, may be investigated quite\nindependently of optics.\n\nBut besides this there was an additional evil.\nA great mathematician was powessed with an\nentirely false notion on the physical origin of\ncolours ; yet, owing to his great authority as a\ngeometer, the mistakes which he committed as\nan experimentalist long became sanctioned id\nthe eyes of a world ever fettered in prejudices.\n\nThe author of the present iaquiry has endea-\nvoured throughout to keep the theory of colours\ndistinct from the mathematics, although there\nare evidently certain points where the assistance,\nof geometry would be desirable. Had not the\nunprejudiced mathematicians, with whom he\nhas had, or still has, the good fortune to be ac-\n\n288 RELATION TO MATHEMATICS.\n\nquainted, been prevented by other occupations\nfrom making common cause with him, his work\nwould not have wanted some merit in this re-\nspect. But this very want may be in the end ad-\nvantageous, since it may now become the object\nof the enlightened mathematician to ascertain\nwhere the doctrine of colours is in need of his\naid, and how he can contribute the means at\nhis command with a view to the complete eluci-\ndation of this branch of physics.\n\nIn general it were to be wished that the Ger-\nmans, who render such good service to science,\nwhile they adopt all that is good from other\nnations, could by degrees accustom themselves\nto work in concert. We live, it must be con-\nfessed, in an age, the habits of which are directly\nopposed to such a wish. Every one seeks, not\nonly to be original in his views, but to be inde-\npendent of the labours of others, or at least to\npersuade himself that he is so, even in the course\nof his life and occupation. It is very often re-\nmarked that men who undoubtedly have accom-\nplished much, quote themselves only, their own\nwritings, journals, and compendiums ; whereas\nit would be far more advantageous for the indi-\nvidual, and for the world, if many were devoted\nto a common pursuit. The conduct of our\nneighbours the French is, in this respect, worthy\n\nTECHNICAL OPERATIONS OF THE DTER. 289\n\nof imitation; we have a pleasing instance in\nCuvier's preface to his \"Tableau E16mentaire\nde THistoire Naturelle des Animaux.\"\n\nHe who has observed science and its pro-\ngress with an unprejudiced eye, might even ask\nwhether it is desirable that so many occupa-\ntions and aims, though allied to each other,\nshould be united in one person, and whether it\nwould not be more suitable for the limited\npowers of the human mind to distinguish, for\nexample, the investigator and inventor, from\nhim who employs and applies the result of ex-\nperiment ? Astronomers, who devote themselves\nto the observation of the heavens and the disco-\nvery or enumeration of stars, have in modern\ntimes formed, to a certain extent, a distinct\nclass from those who calculate the orbits, con-\nsider the universe in its connexion, and more\naccurately define its laws. The history of the\ndoctrine of colours will often lead us back to\nthese considerations.\n\nRELATION TO THE TECHNICAL OPERATIONS OF\n\nTHE DTER.\n\nIf in our labours we have gone out of the\nprovince of the mathematician, we have, on the\nother hand, endeavoured to meet the practical\n\n290 TECHNICAL OPERATIONS OF THE DTSR.\n\nviews of the dyer; and although the chapter\nwhich treats of colour in a chemical point of\nview is not the most complete and circumstan-\ntialy yet in that portion, as well as in our general\nobservations respecting colour, the dyer will find\nhis views assisted far more than by the theory\nhitherto in vogue, which failed to afford him\nany assistance.\n\nIt is curious, in this view, to take a glance\nat the works containing directions on the art of\ndyeing. As the Catholic, on entering his tem-\nple, sprinkles himself with holy water, and after\nbending the knee, proceeds perhaps to converse\nwith his friends on his afiairs, without any espe*\ncial devotion; so all the treatises on dyeing\nbegin with a respectful allusion to the accre*\ndited theory, without afterwards exhiljiting a\nsingle trace of any principle deduced from this\ntheory, or showing that it has thrown light on\nany part of the art, or that it offers any useful\nhints in furtherance of practical metho(te.\n\nOn the other hand, there are men who, after\nhaving become thoroughly and experimentally\nacquainted with the nature of dyes, have not\nbeen able to reconcile their observations with\nthe received theory ; who have, in short, disco*\n\nEELATION TO PHYSIOLOGY AND PATHOLOGY. 291\n\nTered its weak points, and sought for a general\nview more consonant to nature and experience.\nWhen we come to the names of Castel and\nGiilich, in our historical review, we shall have\noccasion to enter into this more fully, and an\nopportunity will then present itself to show that\nan assiduous experience in taking advantage of\nevery accident may, in fact, be said almost to\nexhaust the knowledge of the province to which\nit is confined. The high and complete result is\nthen submitted to the theorist, who, if he ex-\namines facts with accuracy, and reasons with\ncandour, will find such materials eminently\nuseful as a basis for his conclusions. — Note A A.\n\nRELATION TO PHYSIOLOGY AND PATHOLOGY.\n\nIf the phenomena adduced in the chapter\nwhere colours were considered in a physiological\nand pathological view are for the most part\ngenerally known, still some new views, mixed\nup with them, will not be unacceptable to the\nphysiologist. We especially hope to have given\nhim cause to be satisfied by classing certain\nphenomena which stood alone, under analogous\nfacts, and thus, in some measure, to have pre-\npared the way for his further investigations.\n\nThe appendix on pathological colours, again,\n\nu 2\n\n292 RELATION TO NATURAL HISTORY.\n\nis admitted to be scanty and unconnected. We\nreflect, however, that Germany can boast of\nmen who are not only highly experienced in\nthis department, but are likewise so distin-\nguished for general cultivation, that it can cost\nthem but little to revise this portion, to com-\nplete what has been sketched, and at the same\ntime to connect it with the higher facts of\noi^anisation.\n\nRELATION TO NATURAL HISTORY.\n\nIf we may at all hope that natural history\nwill gradually be modified by the principle of\ndeducing the ordinary appearances of nature\nfrom higher phenomena, the author believes he\nmay have given some hints and introductory\nviews bearing on this object also. As colour,\nin its infinite variety, exhibits itself on the sur-\nface of living beings, it becomes an important\npart of the outward indications, by means of\nwhich we can discover what passes underneath.\n\nIn one point of view it is certainly not to be\ntoo much relied on, on account of its indefinite\nand mutable nature; yet even this mutability,\ninasmuch as it exhibits itself as a constant qua-\n}^^y» ^g£^in becomes a criterion of a mutable\nvitality ; and the author wishes nothing more\n\nRELATION TO GENERAL PHTSICS; 293\n\nthan that time may be granted him to develop\nthe results of his observations on this subject\nmore fully; here they would not be in their\nplace.\n\nRELATION TO GENERAL PHYSICS.\n\nThe state in which general physics now is,\nappearS; again, particularly favourable to our\nlabours ; for natural philosophy, owing to inde-\nfatigable and variously directed research, has\ngradually attained such eminence, that it ap-\npears not impossible to refer a boundless empi-\nricism to one centre.\n\nWithout referring to subjects which are too\nfar removed from our own province, we observe\nthat the formulae under which the elementary\nappearances of nature are expressed, altogether\ntend in this direction ; and it is easy to see that\nthrough this correspondence of expression, a\ncorrespondence in meaning will necessarily be\nsoon arrived at.\n\nTrue observers of nature, however they may\ndiffer in opinion in other respects, will agree\nthat all which presents itself as appearance, all\nthat we meet with as phenomenon, must either\n\nfi04 RELATION TO GENERAL FHT8IC8.\n\nindicate an original division which is capable\nof union, or an original unity which admits of\ndiyision, and that the phenomenon will present\nitself accordingly. To divide the united, to\nunite the divided, is the life of nature ; this is\nthe eternal systole and diastole, the eternal col-\nlapsion and expansion, the inspiration and\nexpiration of the world in which we live and\nmove.\n\nIt is hardly necessary to observe that what we\nhere express as number and restrict to dualism\nis to be understood in a higher sense; the ap-\npearance of a third, a fourth order of facts pro-\ngressively developing themselves is to be simi-\nlarly understood; but actual observation should,\nabove all, be the basis of all these expressions.\n\nIron is known to us as a peculiar substance,\ndiiferent from other substances : in its ordinary\nstate we look upon it as a mere material remark-\nable only on account of its fitness for various\nuses and applications. How little, however, is\nnecessary to do away with the comparative insig-\nnificancy of this substance. A two-fold power is\ncalled forth,* which, while it tends again to a\n\n* Eine Entzweyiing geht vor; literally, a dwision iak^s place.\nAccording to some, the two magnetic powers are prevlouely in\nthe bar, and are then separated at the endB.^— T.\n\nBBUTION TO GEHEBAL PBTBICS- 295\n\nState of union, and, as it were, seeks itself, ac-\nquires a kind of magical relation with its like,\nand propagates this double property, which is\nin fact but a principle of reunion, throughout\nall bodies of the same kind. We here first ob-\nserve the mere substance, iron ; we see the divi-\nsion that takes place in it propagate itself and\ndisappear, and ^ain easily become re-excited.\nThis, according to oiir mode of thinking, is a\nprimordial phenomenon in immediate relation\nwith its idea, and which acknowledges nothing\nearthly beyond it\n\nElectricity is again peculiarly characterised.\nAs a mere quality we are unacquainted with it;\nfor us it is a nothing, a zero, a mere point, which,\nhowever, dwells in all apparent existences, and\nat the same time is the point of origin whence,\non the slightest stimulus, a double appearance\npresents itself, an appearance which only mani-\nfests itself to vanish. The conditions under\nwhich this manifestation is excited are infinitely\nvaried, according to the nature of particular\nbodies. From the rudest mechanical friction of\nvery difierent substances with one another, to\nthe mere contiguity of two entirely similar bo-\ndies, the phenomenon is present and stirring,\nnay, striking and powerful, and so decided and\nspecific, that when we employ the terms or for-\n\n296 RELATION TO GENERAL PHYSICS.\n\nmulae polarity, plus and minus, for north and\nsouth, for glass and resin, we do so justifiably\nand in conformity with nature.\n\nThis phenomenon, although it especially af-\nfects the surface, is yet by no means superficial.\nIt influences the tendency or determination of\nmaterial qualities, and connects itself in imme-\ndiate co-operation with the important double\nphenomenon which takes place so universally\nin chemistry, — oxydation, and de-oxydation.\n\nTo introduce and include the appearances of\ncolour in this series, this circle of phenomena\nwas the object of our labours. What we have\nnot succeeded in others will accomplish. We\nfound a primordial vast contrast between light\nand darkness, which may be more generally\nexpressed by light and its absence. We looked\nfor the intermediate state, and sought by means\nof it to compose the visible world of light,\nshade, and colour. In the prosecution of this\nwe employed various terms applicable to the\ndevelopment of the phenomena, terms which\nwe adopted from the theories of magnetism, of\nelectricity, and of chemistry. It was necessary,\nhowever, to extend this terminology, since we\nfound ourselves in an abstract region, and had\nto express more complicated relations.\n\nBBLATION TO OENEBAL FHTSICB. . 207\n\nIf electricity and galTaDism, Id their general\ncharacter, are distinguished as superior to the\nmore limited exhibition of magnetic phenomena,\nit may be said that colour, although coming\nunder similar laws, is still superior ; for since\nit addresses itself to the noble sense of vision,\nits perfections are more generally displayed.\nCompare the varied effects which result from\nthe augmentation of yellow and blue to red,\nfrom the combination of these two higher ex-\ntremes to pure red, and the union of the two\ninferior extremes to green. What a far more\nvaried scheme is apparent here than that in\nwhich magnetism and electricity are compre-\nhended. These last phenomena may be said\nto be inferior again on another account; for\nthough they penetrate and give life to the uni-\nverse, they cannot address themselves to man\nin a higher sense in order to his employing\nthem eesthetically. The general, simple, phy-\nsical law must first be elevated and diversified\nitself in order to be available for elevated uses.\n\n'746.\nIf the reader, in this spirit, recalls what has\nbeen stated by us throughout, generally and in\ndetail, with regard to colour, he will himself\npursue and unfold what has been here only\nlightly hinted at. He will augur well for\n\n396 RELATION TO TH£ THEORY QW MUBIC.\n\nscience, technical processes, and art, if it should\nprove possible to rescue the attractive subject\nof the doctrine of colours from the atomic re-\nstriction and isolation in which it has been\nbanished, in order to restore it to the general\ndynamic flow of life and action which the pre*\nsent age loves to recognise in nature. These\nconsiderations will press upon us more strongly\nwhen, in the historical portion, we shall have to\nspeak of many an enterprising and intelligent\nman who failed to possess his contemporaries\nwith his convictions.\n\nRELATION TO THE THEORY OF MUSIC.\n\nBefore we proceed to the moral associations\nof colour, and the aesthetic influences arising\nfrom them, we have here to say a few words on\nits relation to melody. That a certain relation\nexists between the two, has been always felt ;\nthis is proved by the frequent comparisons we\nmeet with, sometimes as passing allusions,\nsometimes as circumstantial parallels. The\nerror which writers have fajlen into in trying to\nestablish this analogy we would thus define :\n\nColour and sound do not admit of being di-\nrectly compared together in any way, but both\nare referable to a higher formula, both are de^\n\nRELATION TO THE THEOBY OF MUSIC. 290\n\nrivable, although each for itself, from this higher\nlaw. They are like two rivefs which have their\nsource in one and the same mountain, but sul>«\nsequently pursue their way under totally dif-\nferent conditions in two totally different regions,\nso that throughout the whole course of both no\ntwo points can be compared. Both are general,\nelementary effects acting according to the gene-\nral law of separation and tendency to union, of\nundulation and oscillation, yet acting thus in\nwholly different provinces, in different modes,\non different elementary mediums, for different\nsenses*— *Note B B.\n\nCould some investigator rightly adopt the\nmethod in which we have connected the doc-\ntrine of colours with natural philosophy gene-\nrally, and happily supply what has escaped or\nbeen missed by us, the theory of sound, we are\npersuaded, might be perfectly connected with\ngeneral physics ; at present it stands, as it were,\nisolated within the circle of science.\n\nIt is true it would be an undertaking of the\ngreatest difficulty to do away with the positive\ncharacter which we are now accustomed to at-\ntribute to music — a character resulting from the\nachievements of practical skill, from accidental.\n\n300 CONCLUDING OBSERVATIONS ON TBBMINOLOGT.\n\nmathematical > cesthetical influences — and to\nsubstitute for all this a merely physical inquiry\ntending to resolve the science into its first ele-\nments. Yet considering the point at which\nscience and art are now arrived^ considering the\nmany excellent preparatory investigations that\nhave been made relative to this subject^ we may\nperhaps still see it accomplished.\n\nCONCLUDING OBSERVATIONS ON TERMINOLOGY.\n\nWe never sufficiently reflect that a language,\nstrictly speaking, can only be symbolical and\nfigurative, that it can never express things di-\nrectly, but only, as it were, reflectedly. This\nis especially the case in speaking of qualities\nwhich are only imperfectly presented to obser-\nvation, which might rather be called powers\nthan objects, and which are ever in movement\nthroughout nature. They are not to be arrested,\nand yet we find it necessary to describe them ;\nhence we look for all kinds of formulae in order,\nfiguratively at least, to define them.\n\nMetaphysical formulae have breadth ks well\nas depth, but on this very account they require\na corresponding import; the danger here is\nvagueness. Mathematical expressions may in\nmany cases be very conveniently and happily\n\nCONGLUDINO OBSBBTATIONB ON TERinNOLOOT. 301\n\nemployed, but there is always an ioflexibility\nio them, and we presently feel their inadequacy;\nfor even in elementary cases we are very soon\nconscious of an iDcommensurable idea; they\nare, besides, only intelligible to those who are\nespecially conTersant in the sciences to which\nsuch formulae are appropriated. The terms of\nthe science of mechanics are more addressed\nto the ordinary mind, but they are ordinary in\nother senses, and always hare something unpo-\nlished; they destroy the inward life to offer\nfrom without an insufficient substitute for it.\nThe formulae of the corpuscular theories are\nnearly allied to the last ; through them the mu-\ntable becomes rigid, description and expression\nuncouth : while, again, moral terms, which un-\ndoubtedly can express nicer relations, have the\neffect of mere symbols in the end, and are in\ndanger of being lost in a play of wit.\n\nIf, however, a writer could use all these\nmodes of description and expression with per-\nfect command, and thus give forth the result of\nhis observations on the phenomena of nature\nin a diversified language; if he could preserve\nhimself from predilections, still embodying a\nlively meaning in as animated an expression,\nwe might look for much instruction communi-\ncated in the most agreeable of forms.\n\n302 CONCLUDING OB8ERYATION8 ON TEBMINOLOOY.\n\nYet, how difficult it is to ayoid substituting\nthe sign for the thing ; how difficult to keep the\nessential quality still living before us, and not to\nkill it with the word. With all this, we are ex-\nposed in modem times to a still greater danger\nby adopting expressions and terminologies from\nall branches of knowledge and science to em-\nbody our views of simple nature. Astronomy,\ncosmology, geology, natural history, nay religion\nand mysticism, are called in in aid ; and how\noften do we not find a general idea and an ele-\nmentary state rather hidden and obscured than\nelucidated and brought nearer to us by the em-\nployment of terms, the application of which is\nstrictly specific and secondary. We are quite\naware of the necessity which led to the intro-\nduction and general adoption of such a language,\nwe also know that it has become in a certain\nsense indispensable ; but it is only a moderate,\nunpretending recourse to it, with an internal\nconviction of its fitness, that can recommend it.\n\nAfter all, the most desirable principle would\nbe that writers should borrow the expressions\nemployed to describe the details of a given pro-\nvince of investigation from the province itself;\ntreating the simplest phenomenon as an ele-\n\nCONCLUDING OBSERYATIOKS ON TERMINOLOGY. 303\n\nmentary formula, and deriving and developing\nthe more complicated designations from this.\n\nThe necessity and suitableness of such a con-\nventional language where the elementary sign\nexpresses the appearance itself, has been duly\nappreciated by extending, for instance, the ap-\nplication of the term polarity, which is borrowed\nfrom the magnet to electricity, &c. The phu\nand minus which may be substituted for this,\nhave found as suitable an application to many\nphenomena ; even the musician, probably with-\nout troubling himself about these other depart*\nments, has been naturally led to express the\nleading difference in the modes of melody by\nmajor and minor.\n\nFor ourselves we have l<Mig wished to intro^\nduce the term polarity into the doctrine of\ncolours ; with what right and in what sense, the\npresent work may show. Perhaps we may here-\nafter find room to connect the elementary phe-\nnomena together according to our mode, by $,\nsimilar use of symbolical terms, terms which\nmust at all times convey the directly corres-\nponding idea; we shall thus render more ex-\nplicit what has been here only alluded to gene*\nrally, and perhaps too vaguely expressed.\n\nPART VI.\n\nEFFECT OF COLOUR WITH REFERENCE TO MORAL\n\nASSOCLATIONS.\n\nSince colour occupies so important a place in\nthe series of elementary phenomena, filling as it\ndoes the limited circle assigned to it with fullest\nvariety, we shall not be surprised to find that\nits efiects are at all times decided and significant,\nand that they are immediately associated with\nthe emotions of the mind. We shall not be\nsurprised to find that these appearances pre-\nsented singly, are specific, that in combination\nthey may produce an harmonious, characteristic,\noften even an inharmonious efiect on the eye,\nby means of which they act on the mind ; pro-\nducing this impression in their most general ele-\nmentary character, without relation to the nature\nor form of the object on whose surface they are\napparent. Hence, colour considered as an ele-\nment of art, may be made subservient to the\nhighest aesthetical ends. — Note C C.\n\nPeople experience a great delight in colour,\ngenerally. The eye requires it as much as it\nrequires light. We have only to remember the\n\nBBFBBENCE TO MORAL ASSOCIATIONS. 305\n\n/refreshing sensation we experience, if on a\ncloudy day the sun illumines a single portion of\nthe scene before us and displays its colours.\nThat healing powers were ascribed to coloured\ngems, may have arisen from the experience of\nthis indefinable pleasure.\n\nThe colours which we see on objects are not\nqualities entirely strange to the eye ; the organ\nis not thus merely habituated to the impres-\nsion ; no, it is always predisposed to produce\ncolour of itself, and experiences a sensation of\ndelight if something analogous to its own nature\nis offered to it from without ; if its susceptibility\nis distinctly determined towards a given state.\n\nFrom some of our earlier observations we can\nconclude, that general impressions produced by\nsingle colours cannot be changed, that they act\nspecifically, and mast produce definite, specific\nstates in the living organ.\n\nThey likewise produce a corresponding in-\nfluence on the mind. Experience teaches us\nthat particular colours excite particular states\nof feeling. It is related of a witty Frenchman,\n'* II pr^tendoit que son ton de conversation avec\n\n306 REFERENCE TO MORAL ASSOCIATIONS.\n\nMadame 6toit chang6 depuis qu'elle* avoi\nchang6 en cramoisi le meuble de boq cabinet\nqui 6toit bleu.\"\n\nIn order to experience these influences com\npletely, the eye should be entirely surroundec\nwith one colour ; we should be in a room of one\ncolour, or look through a coloured glass. W(\nare then identified with the hue, it attunes the\neye and mind in mere unison with itself.\n\nThe colours on the pltM side are yellow, red-\nyellow (orange), yellow-red (minium, cinnabar).\nThe feelings they excite are quick, lively, as-\npiring.\n\nYELLOW.\n\nThis is the colour nearest the light. It ap-\npears on the slightest mitigation of light, whe^\nther by semi-transparent mediums or faint\nreflection from white surfaces. In prismatic\nexperiments it extends itself alone and widely\nin the light space, and while the two poles re-\nmain separated from each'other, before it mixes\nwith blue to produce green it is to be seen in its\nutmost purity and beauty. How the chemical\nyellow developes itself in and upon the white,\nhas been circumstantially described in its proper\nplace.\n\nYELLOW. 307\n\nIn its highest purity it always carries with it\nthe nature of brightness, and has a serene, gay,\nsoftly exciting character.\n\n767,\n\nIn this state, applied to dress, hangings, car-\npeting, &c., it is agreeable. Gold in its per-\nfectly unmixed state, especially when the effect\nof polish is superadded, gives us a new and high\nidea of this colour; in like manner, a strong\nyellow, as it appears on satin, has a magnificent\nand noble efiect.\n\nWe find from experience, again, that yellow ex^\ncites a warm and agreeable impression. Hence\nin painting it belongs to the illumined and em-\nphatic side.\n\nThis impression of warmth may be experi-\nenced in a very lively manner if we look at a\nlandscape through a yellow glass, particularly\non a grey winter's day. The eye is gladdened,\nthe heart expanded and cheered, a glow seems\nat once to breathe towards us.\n\nIf, however, this colour in its pure and bright\n\nx2\n\n308 YELLOW.\n\nstate is agreeable and gladdening, and in it\nutmost power is serene and noble» it is, on th\nother hand, extremely liable to contaminatior\nand produces a very disagreeable effect if it i\nsullied, or in some degree tends to the minu\nside. Thus, the colour of sulphur, which incline\nto green, has a something unpleasant in it.\n\nWhen a yellow colour is communicated to dul\nand coarse surfaces, such as common clo£h, fell\nor the like, on which it does not appear witi\nfull energy, the disagreeable effect alluded to i\napparent. By a slight and scarcely perceptibl\nchange, the beautiful impression of fire and gol<\nis transformed into one not undeserving th\nepithet foul ; and the colour of honour and jo;\nreversed to that of ignominy and aversion. T\nthis Impression the yellow hats of bankrupt\nand the yellow circles on the mantles of Jews\nmay have owed their origin.\n\nRED-YELLOW.\n\nAs no colour can be considered as stationary\nso we can very easily augment yellow into red\ndish by condensing or darkening it. The colon\nincreases in energy, and appears in red-yellow\nmore powerful and splendid.\n\nRED-TELLOW. 309\n\nAll that we have said of yellow is applicable\nhere in a higher degree. The red-yellow gives\nan impression of warmth and gladness, since it\nrepresents the hue of the intenser glow of fir^\nand of the milder radiance of the setting sun.\nHence it is agreeable around us, and again, as\nclothing, in greater or less degrees is cheerful\nand magnificent. A slight tendency to red im-\nmediately gives a new character to yellow, and\nwhile .the English and Germans content them-\nselves with bright pale yellow colours in leather,\nthe French, as Castel has remarked, prefer a\nyellow enhanced to red ; indeed, in general,\neverything in colour is agreeable to them which\nbelongs to the active side.\n\nYELLOW-RED.\n\nAs pure yellow passes very easily to red-\nyellow, so the deepening of this last to yellow-\nred is not to be arrested. The agreeable,\ncheerful sensation which red-yellow excites, in-\ncreases to an intolerably powerful impression in\nbright yellow-red.\n\nThe active side is here in its highest energy,\nand it is not to be wondered at that impetuous,\nrobust, uneducated men, should be especially\n\n310 YELLOW-RED.\n\npleased with this colour. Among savage natiom\nthe inclination for it has been universally re-\nmarked, and when children, left to themselves\nbegin to use tints, they never spare vermilioo\nand minium.\n\nIn looking steadfastly at a perfectly yellow-\nred surface, the colour seems actually to pene-\ntrate the organ. It produces an extreme ex-\ncitement, and still acts thus when somewhat\ndarkened. A yellow-red cloth disturbs and\nenrages animals. I have known men of educa-\ntion to whom its effect was intolerable if they\nchanced to see a person dressed in a scarlet\ncloak on a grey, cloudy day.\n\nThe colours on the mintis side are blue, red-\nblue, and blue-red. They produce a restless,\nsusceptible, anxious impression.\n\nBLUE.\n\nAs yellow is always accompanied with light,\nso it may be said that blue still brings a prin-\nciple of darkness with it.\n\n779,\nThis colour has a peculiar and almost inde-\n\nBLUE. 311\n\nscribable effect on the eye. As a hue it is power-\nful, but it is on the negative side, and in its\nhighest purity is, as it were, a stimulating\nnegation. Its appearance, then, is a kind of\ncontradiction between excitement and repose.\n\nAs the upper sky and distant mountains\nappear blue, so a blue surface seems to retire\nfrom us.\n\nBut as we readily follow an agreeable object\nthat flies from us, so we love to contemplate\nblue, not because it advances to us, but because\nit draws us after it.\n\nBlue gives us an impression of cold, and thus,\nagain, reminds us of shade. We have before\nspoken of its affinity with black.\n\nRooms which are hung with pure blue, appear\nin some degree larger, but at the same time\nempty and cold.\n\nThe appearance of objects seen through a\nblue glass is gloomy and melancholy.\n\n312 BED-BLUE.\n\nWhen blue partakes in some degree of the\nphs side, the effect is not disagreeable. Sea-\ngreen is rather a pleasing colour.\n\nRED-BLUE.\n\nWe found yellow very soon tending to the in-\ntense state> and we observe the same progres-\nsion in blue.\n\nBlue deepens very mildly into red, and thus\nacquires a somewhat active character, although\nit is on the passive side. Its exciting power is,\nhowever, of a very different kind from that of\nthe red-yellow. It may be said to disturb rather\nthan enliven.\n\nAs augmentation itself is not to be arrested,\nso we feel an inclination to follow the progress\nof the colour, not^ however, as in the case of the\nred-yellow, to see it still increase in the active\nsense, but to find a point to rest in.\n\nIn a very attenuated state, this colour is\nknown to us under the name of lilac ; but even\nin this degree it has a something lively without\ngladness.\n\nBLnE-RED.\n\nThis unquiet feeling increases as the hue pro-\ngresses, and it may be safely assumed, that a\ncarpet of a perfectly pure deep blue-red would\nbe intolerable. On this account, when it is used\nfor dress, ribbons, or other ornaments, it is em-\nployed in a very attenuated and light state, and\nthus displays its character as above defined, in\na peculiarly attractive manner.\n\nAs the higher dignitaries of the church have\nappropriated this unquiet colour to themselves,\nwe may venture to say that it unceasingly as-\npires to the cardinal's red through the restless\ndegrees of a still impatient progression.\n\nWe are here to foi^t everything that borders\non yellow or blue. We are to imagine an ab-\nsolutely pure red, like fine carmine suffered to\ndry on white porcelaiu. We have called this\ncolour \"purpur\" by way of distinction, although\nwe are quite aware that the purple of the an-\ncients inclined more to blue.\n\nWhoever is acquainted with the prismatic\n\n314 BED.\n\norigin of red, will not think it paradoxical if w^\nassert that this colour partly actu^ partly po\ntentid, includes all the other colours.\n\nWe have remarked a constant progress o:\naugmentation in yellow and blue, and seen wha\nimpressions were produced by the various states\nhence it may naturally be inferred that now, ii\nthe junction of the deepened extremes^ a feeling\nof satisfaction must succeed ; and thus, in phy\nsical phenomena, this highest of all appearances\nof colour arises from the junction of two con-\ntrasted extremes which have gradually preparec\nthemselves for a union.\n\nAs a pigment, on the other hand, it present\nitself to us already formed, and is most perfeci\nas a hue in cochineal ; a substance which, how-\never, by chemical action may be made to tenc\nto the plies or the minus side, and may be con-\nsidered to have attained the central point in the\nbest carmine.\n\nThe effect of this colour is as peculiar as ib\nnature. It conveys an impression of gravity\nand dignity, and at the same time of grace ancj\nattractiveness. The first in its dark deep state\n\nBED. 315\n\nthe latter in its light attenuated tint ; and thus\nthe dignity of age and the amiableness of youth\nmay adorn itself with degrees of the same hue.\n\nHistory relates many instances of the jealousy\nof sovereigns with regard to the quality of red.\nSurrounding accompaniments of this colour\nhave always a grave and magnificent efiect.\n\nThe red glass exhibits a bright landscape in\nso dreadful a hue as to inspire sentiments of awe.\n\nKermes and cochineal, the two materials\nchiefly employed in dyeing to produce this\ncolour, incline more or less to the plus or minus\nstate, and may be made to pass and repass the\nculminating point by the action of acids and\nalkalis: it is to be observed that the French\narrest their operations on the active side, as is\nproved by the French scarlet, which inclines to\nyellow. The Italians, on the other hand, remain\non the passive side, for their scarlet has a tinge\nof blue.\n\nBy means of a similar alkaline treatment, the\nso-called crimson is produced ; a colour which\nthe French must be particularly prejudiced\n\n316 GREEN.\n\nagainst, since they employ the expressions —\n'^Sot en cramoisiy m6chant en cramoisi/' to\nmark the extreme of the silly and the repre^\nhensible.\n\nGBEEN.\n\nIf yellow and blue, which we consider as the\nmost fundamental and simple colours, are united\nas they first appear^ in the first state of their\naction, the colour which we call green is the\nresult.\n\nThe eye experiences a distinctly grateful im-\npression from this colour. If the two elementary\ncolours are mixed in perfect equality so that\nneither predominates, the eye and the mind re-\npose on the result of this junction as upon a\nsimple colour. The beholder has neither the\nwish nor the power to imagine a state beyond\nit. Hence for rooms to live in constantly, the\ngreen colour is most generally selected.\n\nCOMPLETENESS AND HARMONY.\n\nWe have hitherto assumed, for the sake of\nclearer explanation, that the eye can be com-\npelled to assimilate or identify itself with a\nsingle colour ; but this can only be possible for\nan •instant.\n\nCOMPLETENEBS AND HASHONT. 317\n\nFor when we find ourselves surrounded by a\ngiven colour which excites its corresponding\nsensation on the eye, and compels us by its pre-\nsence to remain in a state identical with it, this\nstate is soon found to be forced, and the organ\nunwillingly remains in it.\n\nWhen the eye sees a colour it is immediately\nexcited, and it is its nature, spontaneously and\nof necessity, at once to produce another, which\nwith the original colour comprehends the whole\nchromatic scale. A single colour excites, by a\nspecific sensation, the tendency to universality.\n\nTo experience this completeness, to satisfy\nitself, the eye seeks for a colourless space next\nevery hue in order to produce the complemental\nhue upon it.\n\nIn this resides the fundamental law of all\nharmony of colours, of which every one may\nconvince himself by making himself accurately\nacquainted with the experiments which we have\ndescribed in the chapter on the physiological\ncolours.\n\n318 C0MPLETENE8B AND HABMONT.\n\nIf, again, the entire scale is presented to th\neye externally, the impression is gladdening\nsince the result of its own operation is pre\nsented to it in reality. We turn our attentio;\ntherefore, in the first place, to this harmoniou\njuxtaposition.\n\nAs a very simple means of comprehendinj\nthe principle of this, the reader has only t\nimagine a moveable diametrical index in th<\ncolorific circle.* The index, as it revolves rouni\nthe whole circle, indicates at its two extreme\nthe complemental colours, which, after all, ma;\nbe reduced to three contrasts.\n\nYellow demands Red-blue,\nBlue „ Red-yellow,\n\nRed ,, Green,\n\nand contrariwise.\n\nIn proportion as one end of the supposed in\ndex deviates from the central intensity of thi\ncolours, arranged as they are in the natura\norder, so the opposite end changes its place ii\nthe contrasted gradation, and by such a simpl\n\n* Plate 1, fig. 3.\n\nCOMPLETENESS AND HAHHONT. 319\n\ncontrivance the complemental colours may be\nindicated at any given point. A chromatic\ncircle might be made for this purpose, not con-\nfined, like our own, to the leading colours, but\nexhibiting them with their transitions in an un<\nbroken series. This would not be without its\nuse, for we are here considering a very import-\nant point which deserves all our attention.*\n\nWe before stated that the eye could be in\nsome degree pathologically affected by being\nlong confined to a single colour; that, again,\ndefinite moral impressions were thus produced,\nat one time lively and aspiring, at another sus-\nceptible and anxious — now exalted to grand\nassociations, now reduced to ordinary ones. We\nnow observe that the demand for completeness,\nwhich is inherent in the organ, frees us from\nthis restraint; the eye relieves itself by pro-\nducing the opposite of the single colour forced\nupon it, and thus attains the entire impression\nwhich is so satisfactory to it.\n\nSimple, therefore, as these strictly harmo-\nnious contrasts are, as presented to us in the\nnarrow circle, the hint is important, that nature\ntends to emancipate the sense from confined\n\n320 C0MPLBTSNE8B AND HARICONT.\n\nimpressions by suggesting and producing 4\nwhole, and that in this instance we have a i\ntural phenomenon immediately applicable\nSBSthetic purposes.\n\nWhile, therefore, we may assert that the chi\nmatic scale, as given by us, produces an agrc\nable impression by its ingredient hues, we ms\nhere remark that those have been mistaken w]\nhave hitherto adduced the rainbow as an exai\npie of the entire scale; for the chief colou\npure red, is deficient in it, and cannot be pr\nduced, since in this phenomenon, as well as i\nthe ordinary prismatic series, the yellow-rc\nand blue-red cannot attain to a union .\n\nNature perhaps exhibits no general phen<\nmenon where the scale is in complete comb\nnation. By artificial experiments such a\nappearance may be produced in its perfec\nsplendour. The mode, however, in which th\nentire series is connected in a circle, is rendere\nmost intelligible by tints on paper, till aftc\nmuch experience and practice, aided by du\nsusceptibility of the organ, we become penetrate\nwith the idea of this harmony, and feel it preser\nin our minds.\n\n.321\n\nCHARACTERISTIC COMBINATIONS.\n\nBesides these pure, harmonious, self-deve-\nloped combinations, which always carry the\nconditions of completeness with them, there are\nothers which may be arbitrarily produced, and\nwhich may be most easily described by observ-\ning that they are to be found in the colorific\ncircle, not by diameters, but by chords, in such\na manner that an intermediate colour is passed\nover.\n\nWe call these combinations characteristic be-\ncause they have all a certain significancy and\ntend to excite a definite impression ; an impres-\nsion, however, which does not altogether satisfy,\ninasmuch as every characteristic quality of ne-\ncessity presents itself only as a part of a whole,\nwith which it has a relation, but into which it\ncannot be resolved.\n\nAs we are acquainted with the impressions\nproduced by the colours singly as well as in\ntheir harmonious relations, we may at once con-\nclude that the character of the arbitrary combi-\nnations will be very different from each other as\nregards their significancy. We proceed to re-\nview them separately.\n\nY\n\n322 YFXLOW AND RBD— BLUE AND RED.\n\nYELLOW AND BLUE.\n\nThis is the simplest of such combioatio]\n\nIt may be said that it contains too little, :\n\nsince every trace of red is wanting in it, it\n\ndefective as compared with the whole scale. .\n\nthis view it may be called poor, and as the t^\n\ncontrasting elements are in their lowest stai\n\nmay be said to be ordinary ; yet it is recoi\n\nmended by its proximity to green — in short, 1\n\ncontaining the ingredients of an ultimate stat^\n\n«\n\nYELLOW AND RED.\n\nThis is a somewhat preponderating combin\ntion, but it has a serene and magnificent effei\nThe two extremes of the active side are set\ntogether without conveying any idea of pr\ngression from one to the other. As the resu\nof their combination in pigments is yellow-re\nso they in some degree represent this colour.\n\nBLUE AND RED.\n\nThe two ends of the passive side with tl\nexcess of the upper end of the active sid\nThd effect of this juxtaposition approaches tbi\nof the blue-red produced by their union.\n\nTELLOW-RBD AND B{iU£-R£D.\n\nThese, when placed together, as the deepened\nextremes of both sides, have something exciting,\nelevated : they give us a presentiment of red,\nwhich in physical experiments is produced by\ntheir union.\n\nThese four combinations have also the com-\nmon quality of producing the intermediate co-\nlour of our colorific circle by their union, a\nunion which actually takes place if they are\nopposed to each other in small quantities and\nseen from a distance. A surface covered with\nnarrow blue and yellow stripes appears green\nat a certain distance.\n\nIf, again, the eye sees blue and yellow next\neach other, it finds itself in a peculiar disposi-\ntion to produce green without accomplishing it,\nwhile it neither experiences a satisfactory sen-\nsation in contemplating the detached colours,\nnor an impression of completeness in the two.\n\nThus it will be seen that it was not without\nreason we called these combinations character-\nistic ; the more so, since the character of each\n\nY 2\n\n324 COMBINATIONS NON-CHARACTERISTIC.\n\n*\n\ncombination must have a relation to that of 1\nsingle colours of which it consists.\n\nCOMBINATIONS NON-CHARACTERISTIC.\n\nWe now turn our attention to the last kind\ncombinations. These are easily found in t\ncircle ; they are indicated by shorter chords, \\\nin this case we do not pass over an entire int<\nmediate colour, but only the transition from o\nto the other.\n\nThese combinations may justly be called no\ncharacteristic, inasmuch as the colours are t\nnearly alike for their impression to be sign!\ncant. Yet most of these recommend themsely\nto a certain degree, since they indicate a pr\ngressive state, though its relations can hard\nbe appreciable.\n\nThus yellow and yellow-red, yellow-red ar\nred, blue and blue-red, blue-red and red, repr\nsent the nearest degrees of augmentation ar\nculmination, and in certain relations as to quai\ntity may produce no unpleasant effect.\n\nThe juxtaposition of yellow and green hi\n\nRELATION TO LIGHT AND DARK. 325\n\nalways something ordinary, but in a cheerful\nsense ; blue and green, on the other hand, is\nordinary in a repulsive sense. Our good fore-\nfathers called these last fool's colours.\n\nRELATION OF THE COMBINATIONS TO LIGHT\n\nAND DARK.\n\nThese combinations may be very much varied\nby making both colours light or both dark, or\none light and the other dark ; in which modifi-\ncations, however, all that has been found true\nin a general sense is applicable to each parti-\ncular case. With regard to the infinite variety\nthus produced, we merely observe:\n\nThe colours of the active side placed next to\nblack gain in energy, those of the passive side\nlose. The active conjoined with white and\nbrightness lose in strength, the passive gain in\ncheerfulness. Red and green with black appear\ndark and grave ; with white they appear gay.\n\nTo this we may add that all colours may be\nmore or less broken or neutralised, may to a\ncertain degree be rendered nameless^ and thus\ncombined partly together and partly with pure\ncolours; but although the relations may thus\n\n326 CONSIDERATION8 DERIVED FEOM THE\n\nbe varied to infinity, still all that is applicable\nwith regard to the pure colours will be appli-\ncable in these cases.\n\nCONSIDERATIONS DERIVED FROM THE EVIDENCE\nOF EXPERIENCE AND HISTORY.\n\nThe principles of the harmony of colours\nhaving been thus far defined, it may not be\nirrelevant to review what has been adduced in\nconnexion with experience and historical ex-\namples.\n\nThe principles in question have been derived\nfrom the constitution of our nature and the\nconstant relations which are found to obtain in\nchromatic phenomena. In experience we find\nmuch that is in conformity with these principles,\nand much that is opposed to them.\n\nMen in a state of nature, uncivilised nations,\nchildren, have a great fondness for colours in\ntheir utmost brightness, and especially for yel-\nlow-red : they are also pleased with the motley.\nBy this expression we understand the juxtapo-\nsition of vivid colours without an harmonious\nbalance ; but if this balance is observed, through\ninstinct or accident, an agreeable effect may be\nproduced. I remember a Hessian officer, re-\n\nEYIDBNCE OF EXPERIENCE AND HISTORY. 327\n\nturned from America^ who had painted his face\nwith the positive colours, in the manner of the\nIndians ; a kind of completeness or due balance\nwas thus produced, the effect of which was not\ndisagreeable.\n\nThe inhabitants of the south of Europe make\nuse of very brilliant colours for their dresses.\nThe circumstance of their procuring silk stuffs\nat a cheap rate is favourable to this propen-\nsity. The women, especially, with their bright-\ncoloured bodices and ribbons, are always in\nharmony with the scenery, since they cannot\npossibly surpass the splendour of the sky and\nlandscape.\n\n837,\n\nThe history of dyeing teaches us that certain\ntechnical conveniences and advantages have had\ngreat influence on the costume of nations. We\nfind that the Germans wear blue Very generally\nbecause it is a permanent colour in cloth ; so in\nmany* districts all the country people wear green\ntwill, because that material takes a green dye\nwell. If a traveller were to pay attention to\nthese circumstances, he might collect some\namusing and curious facts.\n\nColours, as connected with particular frames\n\n328 CONSIDERATIONS DERIVED FROM THE\n\nof mind, are again a consequence of pecul\ncharacter and circumstances. Lively natio\nthe French for instance^ love intense colot\nespecially on the active side; sedate natio\nlike the English and Germans, wear stra\ncoloured or leather-coloured yellow acco\npanied with dark blue. Nations aiming\ndignity of appearance, the Spaniards and Ii\nlians for instance, suffer the red colour of tb<\nmantles to incline to the passive side.\n\nIn dress we associate the character of ti\ncolour with the character of the person. V\nmay thus observe the relation of colours sing]\nand in combination, to the colour of the coi\nplexion, age, and station.\n\nThe female sex in youth is attached to ros\ncolour and sea-green, in age to violet and darl\ngreen. The fair-haired prefer violet, as opjposi\nto light yellow, the brunettes, blue, as oppose\nto yellow-red, and all on good grounds. Ti\nRoman emperors were extremely jealous wi\nregard to their purple. The robe of the Chine\nEmperor is orange embroidered with red ; h\nattendants and the ministers of religion we\ncitron-yellow.\n\nEVIDENCE OF EXPERIENCE AND HISTORY. 320\n\nPeople of refinement have a disinclination to\ncolours. This may be owing partly to weakness\nof sight, partly to the uncertainty of taste,\nwhich readily takes refuge in absolute negation.\nWomen now appear almost universally in white\nand men in black.\n\nAn observation, very generally applicable,\nmay not be out of place here, namely, that\nman, desirous as he is of being distinguished, is\nquite as willing to be lost among his fellows.\n\nBlack was intended to remind the Venetian\nnoblemen of republican equality.\n\nTo what degree the cloudy sky of northern\nclimates may have gradually banished colour\nmay also admit of explanation.\n\nThe scale of positive colours is obviously soon\nexhausted ; on the other hand, the neutral, sub-\ndued, so-called fashionable colours present infi-\nnitely varying degrees and shades, most of\nwhich are not unpleasing.\n\n330 ESTHETIC INFLUENCE.\n\nIt is also to be remarked that ladies, in wear\ning positive colours, are in danger of making ;\ncomplexion which may not be very bright stil\nless so, and thus to preserve a due balance wit!\nsuch brilliant accompaniments, they are induca\nto heighten their complexions artificially.\n\nAn amusing inquiry might be made whicl\nwould lead to a critique of uniforms, liveries\ncockades, and other distinctions, according t\nthe principles above hinted at. It might h\nobserved, generally, that such dresses and in\nsignia should not be composed of harmoniou\ncolours. Uniforms should be characteristic an<\ndignified ; liveries might be ordinary and strik\ning to the eye. Examples both good and ba\nwould not be wanting, since the scale of colour\nusually employed for such purposes is limitec\nand its varieties have been often enough tried.\n\nESTHETIC INFLUENCE.\n\nFrom the moral associations connected wit\nthe appearance of colours, single or combinec\ntheir aesthetic influence may now be deduce\n\n* Some early Italian writers, Sicillo, Occolti, Rinaldi, ai\nothers, have treated this subject in connexion with the suppom\nsignification of colours. — ^T.\n\nCHIAitOwgCUBO. 331\n\nfor the artist. We shall touch the most essential\npoints to be attended to after first considering\nthe general condition of pictorial representa*\ntion, light and shade, with which the appearance\nof colour is immediately connected.\n\nCHIARO-SCURO.\n\nWe apply the term chiaro-scuro (Helldunkel)\nto the appearance of material objects when the\nmere effect produced on them by light and\nshade is considered. — Note D D.\n\nIn a narrower sense a mass of shadow lighted\nby \"reflexes is often thus designated; but we\nhere use the expression in its first aud more\ngeneral sense.\n\nThe separation of light and dark from all ap-\npearance of colour is possible and necessary.\nThe artist will solve the mystery of imitation\nsooner by first considering light and dark inde-\npendently of colour, and making himself ac-\nquainted with it in its whole extent.\n\nChiaro-scuro exhibits the substance as sub-\nstance, inasmuch as light and shade inform us\nas to degrees of density.\n\n332 cuiABo-scuao.\n\nWe have here to consider the highest li\nthe middle tint, and the shadow, and in the\nthe shadow of the object itself, the shado\ncasts on other objects, and the illumined she\nor reflexion.\n\nThe globe is well adapted for the general\nemplification of the nature of chiaro-scuro,\nit is not altogether sufficient. The softe\nunity of such complete rotundity tends to\nvapoury, and in order to serve as a principle\neffects of art, it should be composed of pi\nsurfaces, so as to define the gradations more\n\nThe Italians call this manner \" il piazzos\nin German it might be called ^'das Flach\nhafte.\"* If, therefore, the sphere is a perJ\nexample of natural chiaro-scuro, a polyj\nwould exhibit the artist-like treatment in wh\nall kinds of lights, half-lights, shadows, {\nreflexions, would be appreciable. — Note E I\n\nThe bunch of grapes is recognised as a g\n\nexample of a picturesque completeness in chia\n\nscuro, the more so as it is fitted, from its fo\n\nto represent a principal group; but it is o\n\n* The English technical expressions ** flat \" and \" squi\nhave an association of mannerism. — T.\n\nCHIARO-SCURO. 333\n\navailable for the master who can see in it what\nhe has the power of producing.\n\nIn order to make the first idea intelligible to\nthe beginner, (for it is difficult to consider it\nabstractedly even in a polygon,) we may take\na cube, the three sides of which that are seen\nrepresent the light, the middle tint, and the\nshadow in distinct order.\n\nTo proceed again to the chiaro-scuro of a\nmore complicated figure, we might select the\nexample of an open book, which presents a\ngreater diversity.\n\nWe find the antique statues of the best time\ntreated very much with reference to these effects.\nThe parts intended to receive the light are\nwrought with simplicity, the portioif originally\nin shade is, on the other hand, in more distinct\nsurfaces to make them susceptible of a variety\nof reflexions ; here the example of the polygon\nwill be remembered. — Note F F.\n\nThe pictures of Herculaneum and the Aldo-\nbrandini marriage are examples of antique\npainting in the same style.\n\n334 TENDENCY TO COLOUR.\n\nModern examples may be found in single\nfigures by Raphael, in entire works by Cor-\nreggio, and also by the Flemish masters, espe*\ncially Rubens.\n\nTENDENCY TO COLOUR.\n\nA picture in black and white seldom makes\nits appearance ; some works of Polidoro are\nexamples of this kind of art. Such works, in-\nasmuch as they can attain form and keeping,\nare estimable, but they have little attraction\nfor the eye, since their very existence supposes\na violent abstraction.\n\nIf the artist abandons himself to his feeling,\ncolour presently announces itself Black no\nsooner inclines to blue than the eye demands\nyellow, which the artist instinctively modifies,\nand introduces partly pure in the light, partly\nreddened and subdued as brown, in the reflexes,\nthus enlivening the whole. — Note G G.\n\nAll kinds of camayeu, or colour on similar\ncolour, end in the introduction either of a com-\nplemental contrast, or some variety of hue.\nThus, Polidoro in his black and white frescoes\n\nTENDENCY TO COLOUR. 336\n\nsometimes introduced a yellow vase/ or some-\nthing of the kind.\n\nIn general it may be observed that men have\nat all times instinctively striven after colour in\nthe practice of the art. We need only observe\ndaily, how soon amateurs proceed from colour-\nless to coloured materials. Paolo Uccello\npainted coloured landscapes to colourless figures.\n—Note H H.\n\nEven the sculpture of the ancients could not\nbe exempt from the influence of this propensity.\nThe Egyptians painted their bas-reliefs ; statues\nhad eyes of coloured stones. Porphyry dra-\nperies were added to marble heads and extremi-\nties, and variegated stalactites were used for the\npedestals of busts. The Jesuits did not fail to\ncompose the statue of their S. Luigi, in Rome,\nin this manner, and the most modem sculpture\ndistinguishes the flesh from the drapery by\nstaining the latter.\n\nKEEPING.\n\nIf linear perspective displays the gradation of\nobjects in their apparent size as affected by dis-\ntance, aerial perspective shows us their grada-\n\n336 KEEPING.\n\ntion in greater or less distinctness, as affect\nby the same cause.\n\nAlthough from the nature of the organ\nsight, we cannot see distant objects so distinct\nas nearer ones, yet aerial perspective is ground\nstrictly on the important fact that all mediui\ncalled transparent are in some degree dim.\n\nThe atmosphere is thus always, more or lei\nsemi-transparent. This quality is remarkal\nin southern climates, even when the baromef\nis high, the weather dry, and the sky cloudle\nfor a very pronounced gradation is observal\nbetween objects but little removed from ea\n\nother.\n\nThe appearance on a large scale is known\nevery one ; the painter, however, sees or t\nlieves he sees, the gradation in the slights\nvarieties of distance. He exemplifies it prac\ncally by making a distinction, for instance,\nthe features of a face according to their relati\nposition as regards the plane of the pictu]\nThe direction of the light is attended to in lil\nmanner. This is considered to produce a gi\ndation from side to side, while keeping has i\nference to depth, to the comparative distinctnc\nof near and distant things.\n\nCOLOURING.\n\nIn proceeding to consider this subject, we\nassume that the painter is generally acquainted\nwith our sketch of the theory of colours, and\nthat he has made himself well acquainted with\ncertain chapters and rubrics which especially\nconcern him. He will thus be enabled to make\nuse of theory as well as practice in recognising\nthe principles of effect in nature, and in em-\nploying the means of art.\n\nCOLOUR IN GENERAL NATURB.\n\nThe first indication of colour announces itself\nin nature together with the gradations of aerial\nperspective ; for aerial perspective is intimately\nconnected with the doctrine of semi-transparent\nmediums. We see the sky, distant objects and\neven comparatively near shadows, blue. At the\nsame moment, the illuminating and illuminated\nobjects appear yellow, gradually deepening to\nred. In many cases the physiological sugges«\ntion of contrasts comes into the account, and\nan entirely colourless landscape, by means of\nthese assisting and counteracting tenderfcies,\nappears to our eyes completely coloured.\n\nCOLOUR OF PARTICULAR OBJECTS.\n\nLfOcal colours are composed of the gener\nelementary colours; but these are determini\nor specified according to the properties of su\nstances and surfaces on which they appea\nthis specification is infinite.\n\nThus, there is- at once a great difierence b\ntween silk and wool similarly dyed. Evei\nkind of preparation and texture produces corr\nsponding modifications. Roughness, smoot\nness, polish, all are to be considered.\n\nIt is therefore one of the pernicious prejudice\nof art that the skilful painter must never attec\nto the material of draperies, but always repr\nsent, as it were, only abstract folds. Is not a\ncharacteristic variety thus done away with, an\nis the portrait of Leo X. less excellent becaut\nvelvet, satin, and moreen, are imitated in the\nrelative effect ?\n\nIn the productions of nature, colours appe^\nmore or less modified, specified, even indiv\ndualised : this may be readily observed in mini\n\nCOLOUR OF PARTICULAB OBJECTS. 339\n\nrals and plants, in the feathers of birds and the\nskins of beasts.\n\nThe chief art of the painter is always to imi-\ntate the actual appearance of the definite hue,\ndoing away with the recollection of the ele-\nmentary ingredients of colour. This difficulty\nis in no instance greater than in the imitation\nof the surface of the human figure.\n\nThe colour of flesh, as a whole, belongs to the\nactive side, yet the bluish of the passive side\nmingles with it. The colour is altogether re-\nmoved from the elementary state and neutralised\nby organisation.\n\nTo bring the colouring of general nature into\nharmony with the colouring of a given object,\nwill perhaps be more attainable for the judicious\nartist after the consideration of what has been\npointed out in the foregoing theory. For the\nmost fancifully beautiful and varied appear-\nances may still be made true to the principles\nof nature.\n\nCHARACTEEISTIC COLOURING.\n\nThe combination of coloured objects, as well\nas the colour of their ground, should depend on\n\nz2\n\n340 CHARACTERISTIC COLOURING.\n\nconsiderations which the artist pre-establishe\nfor himself. Here a reference to the effect c\ncolours singly or combined, on the feelings, i\nespecially necessary. On this account th\npainter should possess himself with the idea g\nthe general dualism, as well as of particula\ncontrasts^ not forgetting what has been adverte\nto with regard to the qualities of colours.\n\nThe characteristic in colour may be compre\nhended under three leading rubrics, which w\nhere define as the powerful, the soft, and th\nsplendid.\n\nThe first is produced by the preponderance c\nthe active side, the second by that of the passiv\nside, and the third by completeness, by the ex\nhibition of the whole chromatic scale in du\nbalance.\n\nThe powerful impression is attained by yellow\nyellow-red, and red, which last colour is to b\narrested on the plus side. But little violet an<\nblue, still less green, are admissible. The sol\neffect is produced by blue, violet, and red, whicl\nin this case is arrested on the minus side; i\nmoderate addition of yellow and yellow-red, bu\nmuch green may be admitted.\n\nUABMONIOUS COLOURING. 341\n\nIf it is proposed to produce both these effects\nin their full significancy, the complemental\ncolours may be excluded to a minimuiiiy and\nonly so much of them may be suffered to appear\nas is indispensable to convey an impression of\ncompleteness.\n\nHARMONIOUS COLOURING.\n\nAlthough the two characteristic divisions as\nabove defined may in some sense be also called\nharmonious, the harmonious effect, properly ^o\ncalled^ only takes place when all the colours are\nexhibited together in due balance.\n\nIn this way the splendid as well as the agree-\nable may be produced ; both of these> however,\nhave of necessity a certain generalised effect,\nand in this sense may be considered the reverse\nof the characteristic.\n\nThis is the reason why the colouring of most\nmodern painters is without character, for, while\nthey follow their general instinctive feeling only,\nthe last result of such a tendency must be mere\ncompleteness; this, they more or less attain,\nbut thus at the same time neglect the charac-\n\n342 HARMONIOUS COLOURING.\n\nteristic impression which the subject might\ndemand.\n\nBut if the principles before alluded to are\nkept in view, it must be apparent that a distinct\nstyle of colour may be adopted on safe grounds\nfor every subject. The application requires, it\nis true, infinite modifications, which can only\nsucceed in the hands of genius.\n\nGENUINE TONE.\n\nIf the word tone, or rather tune, is to be still\nborrowed in future from music, and applied to\ncolouring, it might be used in a better sense\nthan heretofore.\n\nFor it would not be unreasonable to compare\na painting of powerful effect, with a piece of\nmusic in a sharp key ; a painting of soft effect\nwith a piece of music in a flat key, while other\nequivalents might be found for the modifications\nof these two leading modes.\n\nFALSE TONE.\n\nThe word tone has been hitherto understood\nto mean a veil of a particular colour spread over\n\nFALSE TONE. 343\n\nthe whole picture ; it was generally yellow, for\nthe painter instinctively pushed the effect to-\nwards the powerful side.\n\nIf we look at a picture through a yellow glass\nit will appear in this tone. It is worth while to\nmake this experiment again and again, in order\nto observe what takes place in such an opera-\ntion. It is a sort of artificial light, deepening,\nand at the same time darkening the plus side,\nand neutralising the minus side.\n\nThis spurious tone is produced instinctively\nthrough uncertainty as to the means of attain-\ning a genuine effect ; so that instead of com-\npleteness, monotony is the result.\n\nWEAK COLOURING.\n\nIt is owing to the same uncertainty that the\ncolours are sometimes so much broken as to\nhave the effect of a grey camayeu, the handling\nbeing at the same time as delicate as possible.\n\nThe harmonious contrasts are often found to\nbe very happily felt in such pictures, but with-\nout spirit, owing to a dread of the motley.\n\nTHE MOTLEY.\n896,\n\nA picture may easily become party-coloi\nor motley, when the colours are placed next €\nother in their full force, as it were only mech\ncally and according to uncertain impression\n\nIf, on the other hand, weak colours are c<\nbined, even although they may be dissons\nthe effect, as a matter of course, is not striki\nThe uncertainty of the artist is communica\nto the spectator, who, on his side, can neit\npraise nor censure.\n\nIt is also important to observe that the colo\nmay be disposed rightly in themselves, but t]\na work may still appear motley, if they ;\nfalsely arranged in relation to light and shad\n\nThis may the more easily occur as light a\nshade are already defined in the drawing, a\nare, as it were, comprehended in it, while 1\ncolour still remains open to selection.\n\nDREAD OF THEORY.\n\nA dread of, nay, a decided aversion for\n\nULTIMATE AIM— GROUNDS. 345\n\ntheoretical views respecting colour and every-\nthing belonging to it, has been hitherto found to\nexist among painters; a prejudice for which,\nafter all, they were not to be blamed ; for what\nhas been hitherto called theory was groundless,\nvacillating, and akin to empiricism. We hope\nthat our labours may tend to diminish this pre-\njudice, and stimulate the artist practically to\nprove and embody the principles that have been\nexplained.\n\nULTIMATE AIM.\n\nBut without a comprehensive view of the\nwhole of our theory, the ultimate object will not\nbe attained. Let the artist penetrate himself\nwith all that we have stated. It is only by\nmeans of harmonious relations in light and\nshade, in keeping, in true and characteristic\ncolouring, that a picture can be considered com-\nplete, in the sense we have now learnt to attach\nto the term.\n\nGROUNDS.\n\nIt was the practice of the earlier artists to\npaint on light grounds. This ground consisted\nof gypsum, and was thickly spread on linen or\npanel, and then levigated. After the outline\nwas drawn, the subject was washed in with a\n\n346 GROUNDS.\n\nblackish or brownish colour. Pictures prepare\nin this manner for colouring are still in exist\nence, by Leonardo da Vinci, and Fra Bar\ntolomeo; there are also several by Guide—\nNote 1 1.\n\nWhen the artist proceeded to colour, and ha<\nto represent white draperies, he sometimes suf\nfered the ground to remain untouched. Titiai\ndid this latterly when he had attained th<\ngreatest certainty in practice, and could accom<\nplish much with little labour. The whitisl\nground was left as a middle tint, the shadows\npainted in, and the high lights touched on. —\n\nNote K K.\n\nIn the process of colouring, the preparation\nmerely washed as it were underneath, was\nalways effective. A drapery, for example, was\npainted with a transparent colour, the white\nground shone through it and gave the coloui\nlife, so the parts previously prepared for sha-\ndows exhibited the colour subdued, withoul\nbeing mixed or sullied.\n\nThis method had many advantages ; for the\npainter had a light ground for the light portions\nof his work and a dark ground for the shadowed\nportions. The whole picture was prepared ; the\n\nGROUNDS. 347\n\nartist could work with thin colours in the sha-\ndows, and had always an internal light to give\nvalue to his tints. In our own time painting in\nwater colours depends on the same principles.\n\nIndeed a light ground is now generally em-\nployed in oil-painting, because middle tints\nare thus found to be more transparent, and are\nin some degree enlivened by a bright ground ;\nthe shadows, again, do not so easily become\nblack.\n\nIt was the practice for a time to paint on\ndark grounds. Tintoret probably introduced\nthem. Titian's best pictures are not painted on\na dark ground.\n\nThe ground in question was red-brown, and\nwhen the subject was drawn upon it, the\nstrongest shadows were laid in ; the colours of\nthe lights impasted very thickly in the bright\nparts, and scumbled towards the shadows, so\nthat the dark ground appeared through the thin\ncolour as a middle tint. Effect was attained in\nfinishing by frequently going over the bright\nparts and touching on the high lights.\n\n348 GROUNDS.\n\nIf this method especially recommended i\nin practice on account of the rapidity it alio\nof, yet it had pernicious consequences,\nstrong ground increased and became dai\nand the light colours losing their brightness\ndegrees, gave the shadowed portions more\nmore preponderance. The middle tints bee\ndarker and darker, and the shadows at last q\nobscure. The strongly impasted lights a\nremained bright, and we now see only 1\nspots on the painting. The pictures of\nBolognese school, and of Caravaggio, af\nsufficient examples of these results.\n\nWe may here in conclusion observe, 1\nglazing derives its effect from treating the ]\npared colour underneath as a light ground,\nthis operation colours may have the effec\nbeing mixed to the eye, may be enhanced,\nmay acquire what is called tone ; but they t\nnecessarily become darker.\n\nPIGMENTS.\n\nWe receive these from the hands of the c\nmist and the investigator of nature. Much\nbeen recorded respecting colouring substan\n\nPIGMENTS. 349\n\nwhich is familiar to all by means of the press.\nBut such directions require to be revised from\ntime to time. The master meanwhile communi-\ncates his experience in these matters to his\nscholar, and artists generally to each other.\n\nThose pigments which according to their\nnature are the most permanent, are naturally\nmuch sought after, but the mode of employing\nthem also contributes much to the duration of a\npicture. The fewest possible colouring mate-\nrials are to be employed, and the simplest me-\nthods of using them cannot be sufficiently re-\ncommended.\n\nFor from the multitude of pigments colour-\ning has suffered much. Every pigment has its\npeculiar nature as regards its effect on the eye ;\nbesides this it has its peculiar quality, requiring\na corresponding technical method in its appli-\ncation. The former circumstance is a reason\nwhy harmony is more difficult of attainment\nwith many materials than with few, the latter,\nwhy chemical action and re-action may take\nplace among the colouring substances.\n\nWe may refer, besides, to some false ten-\n\n350 PIGMENTS.\n\ndencies which the artists suffer themselves to\nbe led away with. Painters are always looking\nfor new colouring substances, and believe when\nsuch a substance is discovered that they have\nmade an advance in the art. They have a great\ncuriosity to know the practical methods of the\nold masters, and lose much time in the search.\nTowards the end of the last century we were\nthus long tormented with wax-painting. Others\nturn their attention to the discovery of new\nmethods, through which nothing new is accom-\nplished ; for, after all, it is the feeling of the\nartist only that informs every kind of technical\nprocess.\n\nALLEGORICAL, SYMBOLICAL, MYSTICAL APPLICATION\n\nOF COLOUR.\n\nIt has been circumstantially shown above,\nthat every colour produces a distinct impression\non the mind, and thus addresses at once the eye\nand feelings. Hence it follows that colour may\nbe employed for certain moral and assthetic ends.\n\nSuch an application, coinciding entirely with\nnature, might be called symbolical, since the\ncolour would be employed in conformity with\nits effect, and would at once express its mean-\ning. If, for example, pure red were assumed to\n\nALLEGORICAL APPLICATION OF COLOUR. 351\n\ndesignate majesty, there can be no doubt that\nthis would be admitted to be a just and expres-\nsive symbol. All this has been already suffi-\nciently entered into.\n\nAnother application is nearly allied to this ;\nit might be called the allegorical applica-\ntion. In this there is more of accident and\ncaprice, inasmuch as the meaning of the sign\nmust be first communicated to us before we\nknow what it is to signify ; what idea, for in-\nstance, is attached to the green colour, which\nhas been appropriated to hope ?\n\n918,\n\nThat, lastly, colour may have a mystical al-\nlusion, may be readily surmised, for since every\ndiagram in which the variety of colours may be\nrepresented points to those primordial relations\nwhich belong both to nature and the organ of\nvision, there can be no doubt that these may be\nmade use of as a language, in cases where it is\nproposed to express similar primordial relations\nwhich do not present themselves to the senses\nin so powerful and varied a manner. The ma-\nthematician extols the value and applicability\nof the triangle ; the triangle is revered by the\nmystic ; much admits of being expressed in it\nby diagrams, and, among other things, the law\n\n352 ALLEGORICAL APPLICATION OF COLOUR.\n\nof the phenomena of colours ; in this case, in-\ndeed, we presently arrive at the ancient myste-\nrious hexi^ou.\n\nWhen the distinction of yellow and blue is\nduly comprehended, and especially the augmen-\ntation into red, by means of which the opposite\nqualities tend towards each other and become\nunited in a third ; then, certainly, an especially\nmysterious interpretation will suggest itself,\nsince a spiritual meaning may be connected\nwith these facts ; and when we find the two se-\nparate principles producing green on the one\nhand and red in their intenser state, we can\nhardly refrain from thinking in the first case on\nthe earthly, in the last on the heavenly, genera-\ntion of the Elohim. — Note L L.\n\nBut we shall do better not to expose our-\nselves, in conclusion, to the suspicion of enthu-\nsiasm; since, if our doctrine of colours finds\nfavour, applications and allusions, allegorical,\nsymbolical, and mystical, will not fail to be\nmade, in conformity with the spirit of the age.\n\nCONCLUDING OBSERVATIONS.\n\nIn reviewing this labour, which has occupied\nme long, and which at last I give but as a\n\nCONCLUDING OBSERVATIONS. 353\n\nsketch, I am reminded of a wish once expressed\nby a careful writer, who observed that he would\ngladly see his works printed at once as he con-\nceived them, in order then to go to the task with\na fresh eye; since everything defective presents\nitself to us more obviously in print than even in\nthe cleanest manuscript. This feeling may be\nimagined to be stronger in my case, since I had\nnot even an opportunity of going through a fair\ntranscript of my work before its publication,\nthese pages having been put together at a time\nwhen a quiet, collected state of mind was out of\nthe question.*\n\nSome of the explanations I was desirous of\ngiving are to be found in the introduction, but\nin the portion of my work to be devoted to the\nhistory of the doctrine of colours, I hope to give\na more detailed account of my investigations\nand the vicissitudes they underwent. One in-\nquiry, however, may not be out of place here ;\nthe consideration, namely, of the question, what\ncan a man accomplish who cannot devote his\nwhole life to scientific pursuits? what can he\nperform as a temporary guest on an estate not\nhis own, for the advantage of the proprietor ?\n\nWhen we consider art in its higher character,\nwe might wish that masters only had to do with\n\n* Towards the close of 1806, when Weimar was occupied by\nNapoleon after the battle of Jena. — T.\n\n2 A\n\nCONCLUDING 0BSBBTATI0N8.\n\nit, that scholars should be trained by the\nverest study, that amateurs might feel tfa\nselves happy in reverentially approaching\nprecincts. For a work of art should be\neffusion of genius, the artist should eroke\nsubstance and form from his inmost being, t\nhis materials with sovereign command,\nmake use of external influences only to ace\nplish his powers.\n\nBut if the professor in this case has m\nreasons for respecting the dilettante, the ma\nscience has every motive to be still more in<\ngent, since the amateur here is capable of <\ntributing what may be satisfactory and use\nThe sciences depend much more on experin\nthan art, and for mere experiment many a\ntary is qualified. Scientific results are arri\nat by many means, and cannot dispense v\nmany hands, many heads. Science may\ncommunicated, the treasure may be inheri\nand what is acquired by one may be appro\nated by many. Hence no one perhaps ou\nto be reluctant to offer his contributions, i\nmuch do we not owe to accident, to mere pi\ntice, to momentary observation. All who\nendowed only with habits of attention, won\nchildren, are capable of communicating strib\nand true remarks.\n\nIn science it cannot therefore be requii\nthat he who endeavours to furnish somethio)\n\nCONCLUDING OB8EBVATION8. 355\n\nits aid should devote bis whole life to it, should\nsurrey and investigate it in all its extent; for\nthis, in most cases, would be a severe condition\neven for the initiated. But if we look through\nthe history of science in general, especially the\nhistory of physics, we shall find that many im-\nportant acquisitions have been made by single\ninquirers, in single departments, and very often\nby unprofessional observers.\n\nTo whatever direction a man may be deter-\nmined by inclination or accident, whatever\nclass of phenomena especially strike him, excite\nhis interest, fix his attention, and occupy him,\nthe result will still be for the advantage of\nscience: for every new relation that comes to\nlight, every new mode of investigation, even the\nimperfect attempt, even error itself is available;\nit may stimulate other observers and is never\nwithout its use as influencing future inquiry.\n\nWith this feeling the author himself may look\nback without regret on his endeavours. From\nthis consideration he can derive some encou-\nragement for the prosecution of the remainder\nof his task ; and although not satisfied with the\nresult of his efforts, yet re-assured by the sin-\ncerity of his intentions, he ventures to recom-\nmend his past and future labours to the interest\nof his contemporaries and posterity.\n\nMulti pertranaibunt et augebitur ■cientik.\n\nNOTES.\n\nNOTE A.— Par. 18.\nLeonardo da Vinci observes that \" a light object relieved\non a dark ground appears magnified ;\" and again, \" Objects\nseen at a distance appear out of proportion ; this is because\nthe light parts transmit their rajs to the eye more powerfully\nthan the dark. A woman's white bead-dress once appeared\nto me much wider than her shoulders, owing to thnr being\ndressed in black.\"* \" It is now generally admitted that the\nexcitation produced by light is propagated on the retina a\nlitde beyond the outline of the image. Professor Plateau,\nof Ghent, has devoted avery interesting special memoir to\nthe description and explanation of phenomena of this nature.\nSee his ' Memoire sur 1* Irradiation,' published in the Mth\nvol. of the Transactions of the Royal Academy of Sdencet\nat Brussel8.\"+— S. F.\n\nNOTE B.— Par. 23.\n\n\" The duration of ocular spectra produced by strongly\nexciting the retina, may be conveniently measured by\nminutes and seconds ; but to ascertain the duration of more\nevanescent phenomena, recourse must be had to other\nmeans. The Chevalier d'Arcy (Mem. de I'Acad. des Sc.\n\n• \" Trettato della Pittun, Roma, 1817,\" p. 143—223. Thii edition, pnb-\nlished ^m a. Vatican MS., contMn* many ataerratioiii not included in\nfannei editiaiu.\n\nt A few notea (marked with inverted comma* and with the ■ignatuce S. F.)\nhave been kindlf liirniihed by a icientiAc (nend.\n\n358 NOTES.\n\n1765^) endeavoured to ascertain the duration of the impres-\nsion produced by a glowing coal in the following manner.\nHe attached it to the circumference of a wheel, the velocity\nof which was gradually increased until the apparent trace oi\nthe object formed a complete circle, and then measured the\nduration of a revolution, which was obviously that of the\nimpression. To ascertain the duration of a revolution it is\nsufficient merely to know theliumber of revolutions described\nin a given time. Recently more refined experiments of the\nsame kind have been made by Professors Plateau and\nWheaUtone.\"— S. F.\n\nNOTE C— Par. 50.\n\nEvery treatise on the harmonious combination of colours\ncontains the diagram of the chromatic circle more or less\nelaborately constructed. These diagrams, if intended to\nexhibit the contrasts produced by the action and re-action of\nthe retina, have one common defect. The opposite colours\nare made equal in intensity ; whereas the complemental\ncolour pictured on the retina is always less vivid, and always\ndarker or lighter than the original colour. This variety un-\ndoubtedly accords more with harmonious effects in painting.\n\nThe opposition of two pure hues of equal intensity, dif-\nfering only in the abstract quality of colour, would imme-\ndiately be pronounced crude and inharmonious. It would\nnot, however, be strictly correct to say that such a contrast\nis too violent ; on the contrary, it appears the contrast is not\ncarried far enough, for though differing in colour, the two\nhues may be exactly similar in purity and intensity. Com-\nplete contrast, on the other hand, supposes dissimilarity in\nall respects.\n\nIn addition to the mere difference of hue, the eye, it\nseems, requires difference in the lightness or darkness of the\nhue. The spectrum of a colour relieved as a dark on a\nlight ground, is a light colour on a dark ground, and vice\nversa. Thus, if we look at a bright red wafer on the whitest\n\nNOTES. 359\n\nlurf&ce, the complemental ima^ will be Mill lighter than\nthe white surface ; if the same wafer is placed on a black\nsnr&ce, the complemeatal iiiia|[e will be still darker. The\ncolour of both these spectra may be called greenish, but it\nis evident that a colour must be scarcely appreciable as such,\nif it is lighter than white and darker than black. It is,\nhowever, to be remarked, that the white surioce round the\nlight greenish image seems ^ged with a reddish hue, and\nthe black surface round the dark image becomes slightly\nilluminMed with the same colonr, thus in both cases asrist-\ning to render the image apparent (58).\n\nThe difficulty or impossibility of describing degrees of\ncolour in words, has also had a tendency to mislead, by con-\nveying the idea of more porative hues than the pbysiolt^cal\nnmtrart warrants. Thus, supposing scarlet to be relieved\nas a dark, the complemental colour is so light in degree and\nso faint in colonr, that it should be called a pearly grey ;\nwhereas the theorists, looking at the quality of colour ab-\nstractedly, would call it a green- blue, and the diagram\nwould falsely present such a hue equal in intensity to scarlet,\nor as nearly equal as possible.\n\nEven the difference of mass which good taste requires\nmay be suggested by the physiological phenomena, for unless\nthe complemental image is suffered to fall on a surface pre-\ncisely as near to the eye as that on which the original colour\nwas displayed, it appears larger or smaller than the original\nobject (22), and this in a rapidly increasing proportion.\nLastly, the shape itself soon becomes changed (26).\n\nThat vivid colour demands the comparative absence of\ncolour, either on a lighter or darker scale, as its contrast,\nmay be inferred again from the fact that bright colourless\nobjects produce strongly coloured spectra. In darkness,\nthe spectrum which is first white, or nearly white, is fol-\nlowed by red : in light, the spectrum which is first black, is\nfollowed by green (39— 44 ). All colour, as the author ob-\nserves ('259), is (o be conudere<l as half-light, inasmuch as it\n\n300 NOTES.\n\nis in every case lighter than black and darker than whit\nHence no contrast of colour with colour, or even of coloi\nwith black or white, can be so great (as regards lightness <\ndarkness) as the contrast of black and white, or lig^ht an\ndark abstractedly. This distinction between the difference\nof degree and the differences of kind is important, since\njust application of contrast in colour may be counteracte\nby an undue difference in lightness or darkness. The mer\ncontrast of colour is happily employed in some of Guido'\nlighter pictures, but if intense darks had been opposed to hi\ndelicate carnations, their comparative whiteness would haF\nbeen unpleasantly apparent. On the other hand, the flesh\ncolour in Giorg^one, Sebastian del Piombo (his best imi\ntator), and Titian, was sometimes so extremely glowing^ tha\nthe deepest colours, and black, were indispensable accom-\npaniments. The manner of Titian as distinguished fron\nhis imitation of Giorgione, is golden rather than fiery, anc\nhis biographers are quite correct in saying that he was fon<]\nof opposing red (lake) and blue to his flesh, f The cor-\nrespondence of these contrasts with the physiological phe*\nnomena will be immediately apparent, while the occasional\npractice of Rubens in opposing bright red to a 9till coolei\nflesh-colour, will be seen to be equally consistent\n\nThe effect of white drapery (the comparative absence oi\ncolour) in enhancing the glow of Titian*s flesh-colour, has\nbeen frequently pointed out:^ the shadows of white thus\nopposed to flesh, often present, again, the physiological con^\ntrast, however delicately, according to the hue of the cama-\n\n* ** ArditQ vervnente alquanto, sanguigno, e quasi fiammeggiante^\"\n— Zanetti delta Pittura Fenexiana, Yen. 1771, p. 90. Warm as the flesh\ncolour of the colourists is, it still pever approaches a positive hue, if we except\nsome examples in frescoes and other works intended to be seen at a great\ndistance. Zanetti, speaking of a fresco by Oiorgione, now almost obliterated,\ncompares the colour to ** un vivo raggio di cocente tole.^^-^Farie Pitture q\nfretco dei Principa/i Maettri Fenexiani. Ven. 1760.\n\nt RIdolfi.\n\n\\ Zanetti, 1. ii.\n\nNOTES. 361\n\ntion. The lights, on the other hand, are not, and probably\nnever were, quite white, but from the first, partook of the\nquality of depth, a quality assumed by the colourists to per-\nvade eveiy part of a picture more or leu.*\n\nIt was before observed that the description of colours in\nwords may often convey ideas of too positive a nature, and it\nmay be remarked ^nerally that the colours employed by\nthe great masters are, in their ultimate effect, Inore or less\nsubdued or broken. The physiological cxintrasts are, how-\never, still applicable in the most comparatively neutral\nscale.\n\nAgain, the works of the colourists show that these oppo-\nsitions are not confined to large tnassea (except perhaps in\nworks to be seen only at a great distance) ; onthe contrary,\nthey are more or less apparent in every part, and when at\nlast the direct and intentional operations of the artist may\nhave been insufficient to produce them in their minuter\nd^rees, the accidental results of glazing and other methods\nmay be said to extend the contrasts to infinity. In such\nproduction*, where every smallest portion is an epitome of\nthe whole, the eye still appreciates the fascinating efiect of\ncontrast, and the work is pronounced to be true and com-\nplete, in the best sense of the words.\n\nThe Venetian method of scumbling and glazing exhibits\nthese minuter contrasts within each other, and is thus gene-\nrally considered more refined than the system of breaking\nthe colours, since it ensures a fuller gradation of hues, and\nproduces another class of contrasts, those, namely, which re-\nsult from degrees of transparence and opacity. In some of\nthe Flemish and Dutch masters, and sometimes in Keynolds,\nthe two methods are combined in great perfec^on.\n\n* Two great outhorititi, divided by more thaii three centuriea, LeoD Bat-\ntiata Alberli uid Reynoldi, have recommended this nibdued treatmeiit of\nwhite. \" It is to be remembered,\" aaja the finl, \" that no wrface ahould be\nmade w while that it cannot be made mare u. In wfaito dremtu again, it\n18 neceuary to ilop for tliort of the lut degree of wbitenen.\" — Del/a PiUwra,\n1. ii., compare with Ilevnolda, vol. i. dis. V.\n\n362 NOTES.\n\nThe chromatic diagram does not appear to be older dii\nthe last century. It is one of those happy adaptations\nezacter principles to the objects of taste which might ha\nbeen expected from Leonardo da Vinci. That its tn\nprinciple was duly felt is abundandy evident from the wor]\nof the colourists^ as well as from the general observatkx\nof early writers.* The more practical directions occasio]\nally to be met with in the treatises of Leon Battista Alber\nLeonardo da Vinci and others^ are conformable to tl\nsame system. Some Italian works, not written by paintei\nwhich pretend to describe this harmony, are, however, ve\nimperfect, f A passage in Lodovioo Dolce's Dialogue <\nColours is ])erhaps the only one worth quoting. '' He\nsays that writer, \" who wishes to combine colours that a\nagreeable to the eye, will put grey next dusky orange ; yc\nlow*green next rose-colour ; blue next orange ; dark purp]\nblack, next dark-green ; white next black, and white ne\nflesh-colour.*';]; The Dialogue on Painting, by the san\nauthor, has the reputation of containing some- of Titiax\nprecepts : if the above passage may be traced to the sao\nsource, it must be confessed that it is almost the only one\nthe kind in the treatise from which it is taken.\n\nNOTE D.— Par. 66.\nIn some of these cases there can be no doubt that Goeti\n\n* Vasari observes, ** L'unione nella pittura d una discordanca di col\ndiversi accordati insidme.*' — \\o\\. i. c. 18. This obserratiou is repeated\nvarious writers on art in nearly the same words, and at last appears in Se\ndrart : '* Concordia, potissimum picturss decus, in discordift consistit, et qu\nlitigfio colorum.\" — P. i. c. 5. The source, perhaps, is Aristotle : he observ\n\" We are delighted with harmony, because it is the union of contrary prin\npies having a ratio to each other.'* — Problem.\n\nt See « Occolti Trattato de' Colori.\" Parma, 1568.\n\nI <* Volendo Puomo accoppiare insi^me colori che all'occhio dilettino\nporri insidme il berrettino col leonato ; il verde-giallo con Tincarnato e ross\nil turchino con Parangi ; il morello col verde oscuro ; il nero col bianco ;\nbianco con Tincamato.'' — Diaiogo di M, Lodovico Dolce nel quale »i ragio\ndella gualUa, diverutdf e proprieta </•' colori. Veneiia, 1565.\n\n%:-:\n\nNOTES. 363\n\natlributef the contrast too exclusively to the phjnnological\ncause^ without making sufficient allowance for the actual\ndifference in the colour of the lights. The purely physical\nnature of some coloured shadows was pointed out by Pohl-\nmann; and Dr. Eckermann took some pains to connnce\nGoethe of the necessity of making such a distinction.\nGoethe at first adhered to his extreme view^ but some time\nafterwards confessed to Dr. Eckermann, that in the case of\nthe blue shadows of snow (74), the reflection of the sky\nwas undoubtedly to be taken into the account. ''Both\ncauses may, however, operate together,\" he observed, '' and\nthe contrast which a warm yellow light demands may\nheighten the effect of the blue.*' This was all his opponent\ncontended.*\n\nWith a few such exceptions, the general theory of Goethe\nwith regard to coloured shadows is undoubtedly correct ;\nthe experiments with two candles (68), and with coloured\nglass and fluids (80), as well as the observations on the\nshadows of snow (75), are conclusive, for in all these cases\nonly one light is actually changed in colour, while the other\nstill assumes the complemental hue. '* Coloured shadows,\"\nDr. J. Miiller observes, \" are usually ascribed to the phy-\nsiological influence of contrast ; the complementary colour\npresented by the shadow being regarded as the effect of\ninternal causes acting on that part of the retina, and not of\nthe impression of coloured rays from without. This expla-\nnation is the one adopted by Rumford, Goethe, Grotthuss,\nBrandes, Tourtual, Pohlmann, and most authors who have\nstudied the subject.\"f\n\nIn the Historical Part the author gives an account of a\nscarce French work, \" Observations sur les Ombres Colo-\nrees,\" Paris, 1782. The writerj concludes that \" the colour\n\n* Eckermann's ** GesprUche mlt Goethe,*' vol. ii. p. 76 and 280.\nf ** Elements of Physiology,'' by J. Miiller, M.D., translated from the Ger-\nman by William Baly, M.D. London, 1839.\n\nX Anonymous, having only given the initials H. F. T.\n\n364 NOTES.\n\nof shadows is as much owing to the light that causes tkem\n\nas to that which (more faintly) illumines them.*^\n\nNOTE E.— Par. 69.\n\nThis opinion of the author is frequently repeated (£01,\n312> 59 1)^ and as it seems at first sight to be at variance\nwith a received principle of art^ it may be as well at onoe to\nexamine it.\n\nIn order to see the general proposition in its true point\nof view, it will be necessary to forget the arbitrary distinc«\ntions of light and shade^ and to consider all sucb modifica-\ntions between highest brightness and absolute darkness only\nas so many lesser degrees of light* The author, indeed,\nby the word shadow, always understands a lesser light.\n\nThe received notion, as stated by Du Fresnoy,f is much\ntoo positive and unconditional, and is only true when we\nunderstand the '^ displaying*' light to comprehend certain\ndegrees of half or reflected lights and the ''destroying**\nshade to mean the intensest degree of obscurity.\n\nThere are degrees of brightness which destroy colour as\nwell as degrees of darkness.]] In general, colour resides in\na mitigated light, but a very little observation shows us that\ndifferent colours require different degrees of light to display\nthem. Leonardo da Vinci frequently inculcates the general,\nprinciple above alluded to, but he as frequently qualifies it ;\nfor he not only remarks that the highest light may be com-\n\n• Leonardo da Vinci observes : \" L*ombra d diminuxione di luce, tenebre <\nprivatioue di luce.\" And again : « Sempre il minor lume i ombra del lame\nmaggiore.\"— 7Va//o/o del/a Pittura, pp. 274-299.\n\nN. B. The same edition before described has been consulted throughout,\nt *' liux varium vivumque dabit, nullum umbra colorem.\"\n\nDe ArU Graphic^.\n\" Know first that light displays and shade destroys\nRefulgent nature's variegated dies.\" — Mason^s Trantlation,\nX A Spanish writer, Diego de Carvalho e Sampayo, quoted by Goethe ('* Far-\nbeulehre,\" vol. ii.}, has a similar observation. This destroying effect of light\nin striking in climates where the sun is powerful, and was not likely to\nthe notice of a Sjianiard.\n\nNOTES. 365\n\nparative privation of colour, but observes^ with great truths\nthat some hues are best displayed in their fully illumined\nparts, some in their reflections, and some in their half-\nlights ; and again, that every colour is most beautiful when\nlit by reflections from its own surface, or from a hue similar\nto its own.*\n\nThe Venetians went further than Leonardo in this view\nand practice ; and he seems to allude to them when he cri-\nticises certain painters, who, in aiming at clearness and\nfulness of colour, neglected what, in his eyes, was of supe-\nrior importance, namely, gradation and force of chiaro-\nscuro.+\n\nThat increase of colour supposes increase of darkness, as\nso often stated by Goethe, may be granted without difficulty.\nTo what extent, on the other hand, increase of darkness, or\nrather diminution of light, is accompanied by increase of\ncolour, is a question which has been variously answered by\nvarious schools. Examples of the total negation of the\nprinciple are not wanting, nor are they confined to the in-\nfancy of the art. Instances, again, of the opposite tendency\nare frequent in Venetian and early Flemish pictures resem-\nbling the augmenting richness of gems or of stained glass :^\n\n* Trattato, pp. 103, 121, 123, 324, &c.\n\nt lb. pp. 85, 134.\n\nX Absolute opacity, to judge from the older specimens of stained glass,\nseems to hare been considered inadmissible, liie window was to admit light,\nhowever modified and varied, in the form prescribed by the architect, and\nthat form was to be preserved. This has been unfortunately lost sight of in\nsome modem glass-painting, which, by excluding the light in large masses,\nand adopting the opacity of pictures (the reverse of the influence above al-\nluded to), has interfered with the architectural symmetry in a manner (ar\nfrom desirable. On the other hand, if we siq>pose painting at any period to\nhave aimed at the imitation of stained glass, such an imitation must of neces-\nsity have led to extreme force ; for the painter sets out by substituting a mere\nwhite ground for the real light of the sky, and would thus be compelled to\nsubdue every tone accordingly. In such an imitation his colour would soon\ndeepen to its intensest state ; indeed, considerable portions of the darker hues\nwould be lost in obscurity. The early Flemish pictures seldom err on the side\nof a gay superabundance of colour ; on the contrary, they are generally re-\n\n366 N0TB8.\n\nindeed^ it is not impossible that the increase of colour in\nsbade^ which is so remarkable in the pictures alluded to,\nmay have been originally suggested by the rich and £uci-\nnating effect of stained glass ; and the Venetians, in this as\nin many other respects, may have improved on a hint bor*\nrowed from the early German painters, many of whom\npainted on glass. '^\n\nAt all events, the principle of still increasing in colour in\ncertain hues seems to have been adopted in Flanders and in\nVenice at an early period ;f while Giorgione, in carrying\nthe style to the most daring extent, still recommended it by\ncorresponding grandeur of treatment in other respects.\n\nThe same general tendency, except that the technical\nmethods are less transparent* is, however, very striking in\nsome of the painters of the school of Umbria, the instruc-\ntors or early companions of Raphael.]: The influence of\n\nmarkable for comparatively cool lights, for extreme depth, and a certain mb-\ndued splendour, qualities which would necessarily result horn the imitation or\ninfluence in question.\n\n* See Langlois, '* Peinture sur Verre.\" Rouen, 1832 ; Descamps, ** La Vie\ndes Peintres Flamauds ;\" and Oessert, ** G^eschichte der Glasmalerei.'' Stat-\ngard, 1839. The antiquity of the glass manufactory of Murano (Venice} is al^ft\nnot to be forgotten. Vasari objects to the Venetian glass, because it was darker\nin colour than that of Flanders, France, and England ; but this very quality\nwas more likely to have an advantageous influence on the style of die early oil-\npainters. The use of stained glass was, however, at no period very general in\nItaly.\n\nt 2^etti, \" Delia Pittura Venesiana,\" marks the progress of the early Ve-\nnetian painters by the gradual use of the warm outline. Hiere are some\nmosaics in St. Mark's which have the effect of flesh-colour, but on examina-\ntion, the only red colour used is found to be in the outlines and markii^s.\nMany of the drawings of the old masters, heightened with red in the shadowv,\nhave the same effect. In these drawings the artists judiciously avoided eo-\nlouring the lips and cheeks much, ibr this would only have betrayed the want\nof general colour, as is observable when statues are so treated.\n\nI Andrea di Luigi, called L'Ingegno, and Niccolo di Foligno, are cited as\nthe most prominent examples. See Rumohr, ** Italienisehe Forschongen.\"\nPerugino himself occasionally adopted a very glowing colour.\n\nThe early Italian schools which adhered most to the Bysantine types i^pear\nto have been also the most remarkable for depth, or rather darkness, of colour.\nThis fidelity to customary representation was sometimes, as in the schools of\n\nNOTES. 367\n\nthese examplei, as well u that of Frs Bartolommeo, in\nFlorence, is diitinctly to be traced in the works of the great\nartist just named, but neither is so marked as the effect of\nhis emulation of a Venetian painter at a later period. The\nglowing colour, sometimes bordering on exaggeration, which\nRaphael adopted in Rome, is undoubtedly to be attri-\nbuted to the rivalry of Sebastian del Piombo. This painter,\nthe best of Giorgione's imitators, arrived in Rome, invited\nby Agostini Chigi, in 1511, and the most powerful of Ra-\nphael's frescoes, the Heliodonu and Mass of Bolsena, as\nwell as some portraits in the same style, were p^ted in the\ntwo following years. In the hands of some of Raphael'f\nscholars, again, this extreme warmth was occasionally car-\nried to excess, particolarly by Pierino del Vaga, with whom\nit often degenerated into redness. The representative of\nthe glowing manner in Florence was Fra Bartolommeo, and,\nin the same quality, conndered abstractedly, some painters\nof the school of Ferrara were second to none.\n\nIn another Note (par. 177) some further oonnderationa\n\nUmbria, and to m cerUin eit«nt in ihoae of Siena uiil Bologna, the result of\na religioai veneration for the ancient eiomplea ; in othaiB, ai in Venice, tlw\ncircuniitance of frequent inlercoune with the LeTsiit ia alto to be taken ioto\nthe account. Tbe Greek picture) of the MadDnno, not to mention other lepra-\n■entationi, were extremely dark, in exaggerated conformity, it ia nippoead,\nwith the tradition reepectitig her real compleiiou (see D'Agiiiconrt,vol. iv.\np. 1) ; a belief which obtained lo laid a* Lomouo'* time, tai, ipeaking of the\nMadonna, he obierret, \" L^geai perA che fu alquanlo bruna.\" Qiotio, who\nwith the iudependence of geniua betrayed a certain contempt for th«e trodi-\ntimi, failed perhapt to unite improrement with norelty when he eiibitilated a\npale white fleah-colonr tot the ttaditional brown. Some apecimoni of hia\nworks, (till exiatitig at Padua, preoent a remarkable controat in thi* reapeet\nwith the'earlieet productions of the Venetian and Paduan artists. Hia work*\nat Florence differ a« widely from thoM of the earlier paintere of Tiacany.\nThis peculiarity wai inherited by hia imiUton, and at one time aJmoat chonc-\ntcriied the Florentine school. Leon Battiata Alberti was not perhapt the\nfint irho Directed to it (\" Vorrei io che dai pittori tbtae comperato il color\nbianco aasai piil caro che le preiionsaime gemme.\" — Diiia Pilliira,l. ii.}\nThe attachment of Fra Bartolommeo to the grave characlei of the Chriitian\ntypes 18 eiempliflcd in hi« depp coloujing, at well aa in other reqwctt.\n\n368 NOTES.\n\nare offered, which may partly explain the prevalence of thtf\nstyle in the beginning of the sixteenth century ; here we\nmerely add, that the conditions under which the appearance\nitself is most apparent in nature are perhaps more obvious\nin Venice than elsewhere. The colour of general nature\nmay be observed in all places with almost equal conve-\nnience, but with regard to an important quality in living\nnature, namely, the colour of flesh, perhaps there are no\ncircumstances in which its effects at different distances can\nbe so conveniently compared as when the observer and the\nobserved gradually approach and glide past each other on\nso smooth an element and in so undisturbed a manner as\non the canals and in the gondolas of Venice ;* the <x>m-\nplexions, from the peculiar mellow carnations of the Italian\nwomen to the sun-burnt features and limbs of the mariners,\npresenting at the same time the fullest variety in another\nsense.\n\nAt a certain distance — ^the colour being always assumed\nto be unimpaired by interposed atmosphere — the reflections\nappear kindled to intenser warmth ; the fiery glow of Gior-\ngione is strikingly apparent ; the colour is seen in its largest\nrelation ; the macchia,-\\ an expression so emphatically used\nby Italian writers, appears in all its quantity, and the re-\nflections being the focus of warmth, the hue seems to\ndeepen in shade.\n\nA nearer view gives the detail of cooler tints more per-\nceptibly,;}: and the forms are at the same time more distinct.\nHence Lanzi is quite correct when, in distinguishing the\nstyle of Titian from that of Giorgione, he says that Titian's\n\n* Holland might be excepted, and in Holland nmilar causes may have\nhad a similar influence.\n\nf Local colour ; literally, the hioi.\n\nX Zanetti ventures to single out the picture of Tobit and the Angel in 8.\nMarziale as the first example of Titian's own manner, and in which a direct\nimitation of Giorgione is no longer apparent. In this picture the lights ara\ncool and the hlood-tint very effective.\n\n3«9\n\nwu at once more defiiied and less fiery.* In a still nearer\nobservation the eye detects the minute lights which Leo-\nnardo da Vinci says are incompatible with effects such as\nthose we have described, f and which, accordingly, we never\nfind in Giorgione and Titian. This large impression of\ncolour, which seems to require the condition of comparative\ndistance for its full effect, was most fitly employed by the\nsame great artists in works painted in the open air or for\nlarge altar-pieces. Their celebrated frescoes on the exterior\nof the Fondaco de' Tedeschi at Venice, to judge from their\nfaint remains and the descriptions of earlier writers, were\nremarkable for extreme warmth in the shadows. The old\nfrescoes in the open air throughout Friuli have often the\nsame character, and, owing ti> the fulness of effect which this\ntreatment ensures, arc conspicuous at a very great distance.^\nIn assuming that the Venetian ptunters may have ac-\nquired a taste for this breadth^ of colour under the drcum-\nslances above alluded to, it is moreover to be remembered\nthat the time for this agreeable study was the evening;\nwhen the sun had already set behind tbe hills of Bassano ;\nwhen the light was glowing but diffused; when shadows\n\n■ \" Meno (fimialo, men tocaio.\" — Storia Piltarica.\n\nf ** \\a prima co»a cbe de' i^Idt! si perde nelle diAtanzc i il liutro, loro mi-\nnima parte.\" — Trallalo,^. 213; and elsewhere, \"I lumi principali in pjcciol\nluogoioii quoUi cha in picciala diitania aono i primiclie ai peidono all' occhia.\"\n—p. 128.\n\nI A calosaal St. Chriilopher, the usual subject, is frequently seen occupying\nthe whole height of tbe eitemal wall of a chucch. We have here an example\nof (he influence of religion, such as it was, even an the style of colouring and\npractical methods of the art. The mere light of the image of St. Chrialopher,\nthe type of strei^b, was considered nuflficient lo reinvigorale (hose who were\neihautled by the labours of husbandry. Tbe following is a specimen of tbe\ninKiiplions inculcating Ibi* belief : —\n\n\" Christopburi Sancti speciem qiiicumque tuetur,\nlllo namque die nullo languote teuetur.\"\nHence tbe practice of painting the figure on the outside of churches, hence its\ncdIosmI size, and hence the powerful qualitiea in coluui slwie described. Sea\nManiago. \" Storia delle Belle Arti Friulane.\"\n\n^ Tbe authority of Fusel! sufficjenlly watraata the application of the term\nbreadth to colour ; he speak* of Titian's \" breadth orloca] tint.\"\n2 B\n\n370 NOTES.\n\nwere soft — conditions all agreeing with the charact\ntheir colouring:* above all, when the hour invitee\nfairer portion of the population to betake themaelvi\ntheir gondolas to the lagunes. The scene of this ''pr\nnade\" was to the north of Venice, the quarter in ^\nTitian at one time lived. A letter exists written by I\ncesco Priscianese, giving an account of his supping\nthe great painter in company with Jacopo Nardi, F\nAretino, the sculptor Sansovino, and others. The w\nspeaks of the beauty of the garden, where the table\nprepared, looking over the lagunes towards Murano, ** w\npart of the sea/' he continues, *' as soon as the sun\ndown, was covered with a thousand gondolas, graced\nbeautiful women, and enlivened by the harmony of ¥<\nand instruments, which lasted till midnight, fomun\npleasing accompaniment to our cheerful repast.'* f\n\nTo return to Goethe : perhaps the foregoing remarks\nwarrant the conclusion that his idea of colour in shade\nnot irrecondleable with the occasional practice of the\npainters. The highest examples of the style thus def\nare, or were, to be found in the works of Giorgione^\nTitian, and hence the style itself, though '^ within that <ii\n\n* Zanetti quotes an opinion of the painters of his time to the same dflfo\n<* Teneano essi (alcimi maestri) per cosa certa, che in molte opere Ti\nvol esse fingere il lame— quale si vede nelV incliuard del sole verso la\nGli orizionti assai luminosi dietro le montagne, le ombre incerte e pid 1<\nnagioni brunette e rosseggianti ddle figure, gl'induceano a creder quest(\nLib. ii. Leonardo da Vinci observes, \" Quel corpo che si troveri in med\nlume fia in lui poca differenza da' lumi all' ombre. E questo accade si\ndella sera — e queste opere sono dolci ed hacci graxia ogni qualiti di vi\n&c. — p. 336. Elsewhere, \" Le ombre fatte dal sole od altri lumi partic\nsono sensa grasia.\" — p. 357 ; see also p. 247.\n\nt See *' Francesco Priscianese De* Primi Principii della Lingua Lat\nVenice, 1550. The letter is at the end of the work. It is quoted in Tic\n\" Vite de» Pittori Vecelli,\" Milan, 1817.\n\n\\ The works of Giorgione are extremely rare. The pictures best calcu\nto give an idea of the glowing mamicr for which he is celebrated, an\nsomewhat early works and several of the altar-pioccs of Titian, the\nspecimens of Palma Vecchio, and the portraits of Sebastian del Piombo»\n\nNOTES. 37 1\n\nfew \"dare walk,\" is to be coiuiilered the graiidett and most\nperfect. Ita pmaible defects or abuse are not tw be dia-\nscmbled : in addition to tbe danger of ezaggeratioo* it is\n■eldom united with' tbe plenitude of light and shade, or\nwith roundness ; yet, where fine examples of both modes of\ntreabnent jnay be compared, the charm of colour has per-\nhaps the adTantage.f Tbe difficulty of uniting qualities so\ndifferent in their nature, is proved bj tbe very rare instances\nin which it has been accomplished. Tintoret in endeavonr-\ning to add cbiaio-scuro to Venetian colour, in atinost every\ninstance fell short of the glowing richness of Titian.^\n\n* Zwwtti and LodDticD Dolce mcntiDii Loranio Lotto u an iniUnc* of the\nezceu of Oioigioue'i ityle. Titim hinuelf lonistuiiM ovcnf epped tbe muk,\nai bu biogrqiliei* caattm, and ai appean, among otbet inataDcei, from tbe\nhead of St. Feler in the jncluce (iui« in ths Vatican) in which the eelebialed\nSt- Sebaatian ii iotrodaced. IU(ihael waa eritielaed by tome caidioal* fbi a\n•imilai defect. See \" Caitiglione, 11 Cortigiano,\" 1. ii.\n\nIn tbe aame paitgtaph to which the preeeot obaerratioiu refer, tbe autborilj\nof Kireherii quoted ; bia tieatiee, \" An magna lucii etumbrc,\" wa« puUiihed\nill Rome in IG4G. Id a portnit of Nicboiai Pouaain, engraied by Clouet, tbe\npainter ia repreeeuted holding a book, which, from the title and the eircnm-\n•lance of Pouuia having lired in Rome iu Kiicher'a time, Goethe auppout to\nbe Ibe work in queation. The abuaa of the piinciple aboie alluded to, ii pei-\nhapa eiemplitted in the ted half-tinta obaeirable iu tome of Pauaain'a flgun*.\n\nThe augroeatstiDn of coloni in aibdned light wai atill more directly taught\nby LamanO' He compoaea the half-tinla of fleah merely by diminiahicig tbe\nquantity ofwhite, the propoitionaofthe other colouia employed (for be enteii\niolo minute detaila) remaining unaltered. See bia \" Tiollato della arte della\nPittuiB,\" Milan, 1584, p. 301.\n\nt In tbe Dreaden Gallery, a pictuie attributed to Tidau — at all ereuta a\nlucid Venetian picture — hanga next the St. Oeoige of Coneggiu. Aftei\nlooking at the latter, tbe Venetian work appean glaeay and unnUKtBuliBi, but\non reveraing theoideiof compariaaD,lheCarrqgia may he aaid to suffer more,\nand for a moment its fine tranutioua of light and shade seem changed to\nheavineaa.\n\nI The finest worka ofnntoret— the Crucifixion aud the Miracato del Servo\n(consdared beie merely with reference lt>~ their colour,) may be aaid to\ncombine the eiEeUencee of Titian and Oiococoo Baasao, ou a grand acole ; the\nsparkling claoruesa of the latter ia oiie of tbe promineut characteristica of\nthese pictures. Tintoret is reported to have once aaid that a union of hie ovu\nknowledge of foim with Boaaan's colour would be the perfection of paintiug.\nSee \" Verci Notiiie do' Pittori di Doasano ;\" Yen. 1775, p. 61.\n\n372 NOTES,\n\nGiacomo Bassan and his imitators, even in their dark effect!\nstill had the principle of the gem in view : their light, ii\ncertain hues, is the minimum of colour, their lower tones ar\nrich, their darks intense, and all is sparkling.* Of the gres\npainters who, beginning, on the other hand, with chiarc\nscuro, sought to combine with it the full richness of coloui\nCorreggio, in the opinion of many, approached perfectioi\nnearest; but we may perhaps conclude with greater justic\nthat the desired excellence was more completely attained b\nRembrandt than by any of the Italians.\n\nNOTE F— Par. 83.\n\nThe author, in these instances, seems to be anticipatinj\nhis subsequent explanations on the effect of semi-transparea\nmediums. For an explanation of the general view container\nin these paragraphs respecting the gradual increase of co-\nlour from high light, see the last Note.\n\nThe anonymous French work before alluded to, amon^\nother interesting examples, contains a chapter on shadowi\ncast by the upper light of the sky and coloured by thi\nsetting sun. The effect of this remarkable combination is\nthat the light on a wall is most coloured immediately undei\na projecting roof, and becomes comparatively neutralised in\nproportion to its distance from the edge of the darkest shade.\n\nNOTE G.— Par. 98.\n\n'* The simplest case of the phenomenon, which Goethe\ncalls a subjective halo, and one which at once explains its\ncause, is the following. Regard a red wafer on a sheet of\nwhite paper, keeping the eye stedfastly fixed on a point at\n\n* That this last quality, the characteristic of Bassan's best pictures, waa\nheld in high estimation by Paul Veronese, is not only evident from that\npunter's own works, but from the circumstance of his preferring to place his\nsons with Bassan rather than with any other painter. (See \" Boschini Carta del\nNavegar,\" p. 280.) The Baptism of Sta. Lucilla, in Boschini's time con-\nsidered the finest of Giacomo's works, is still in the church of S. Valentino, at\nBassano, and may be considered the type of the lucid and sparkling manner.\n\nNOTES. 373\n\nIts center. When the retina is fatigued, withdraw the head\na little from the paper, and a greea halo will appear to tur-\nround the wafer. By this slight increase of distance the\nimage of the wafer itself on the retina becomes smaller, and\nthe ocular spectrum which before coincided with the direct\nimage, being now relatively larger, is seen as a surrounding\nring.\"— S. F. Goethe mentions cases of this kind, but doea\nnot class them with subjective halos. See Par. 30.\n\nNOTE H.— Par. 113.\n\"Cases of this kind are by no means uncommon. Several\ninteresting ones are related in Sir John Herschell's article on\nLight in the Encyclopaedia Metropolitana. Careful inves-\ntigation has, however, shown that this defect of vision arises\nin most, if not in all cases, from an inability to perceive the\nred, not the blue rays. The terms are so confounded by the\nindividuals thus affected, that the comparison of colours in\niheir presence is the only criterion.\" — S. F.\n\nNOTE 1.— Par. 133.\nThe author more than once admits that this chapter on\n\" Pathological Colours\" is very incomplete, and expresses a\nwish (Par. 734) that some medical physiologists would in-\nvestigate the subject further. This was afterwards in a\ngreat degree accomplished by Dr. Johannes MUller, in his\nmemoir \" Uber die Phantastiscben Gesichtseracheinungen.\"\nCoblcntz, 1826. Similar phenomena have been also in-\nves^gated with great labour and success by Purkinje. For\na collection of extraordinary facts of the kind recorded by\nthese writers, the reader may consult Scott's Letters on\nDemonology and Witchcraft.* The instances adduced by\nMiiller and others are, however, intended to prove the in-\nherent capacity of the organ of vision to produce light and\ncolours. In some maladies of the eye, the patient, it seems,\n\n■ See uliio ■ curious pawage on tbe beatifii: vuion of the monlu of Moont\nAthiw, ill Gibbon, chaji. fiS.\n\n374 NOTES.\n\nsuffers the constant presence of light without external lig\nThe exciting principle in this case is thus proved to\nwithin, and the conclusion of the physiologists is that <\ntemal light is only one of the causes which produce lum:\notts and coloured impressions. That this view was anti\npated by Newton may be gathered from the*concladi\n'^ query\" in the third book of his Optics.\n\nNOTE K.— Par. 140.\n\n\"Catoptrical colours. The colours included under tl\nhead are principally those of fibres and grooved surface\nthey can be produced artificially by cutting parallel grooi\non a surface of metal from 2000 to 10,000 in the inch. S\n' Brewster's Optics/ p 120. The colours called by Goet\nparoptical, correspond with those produced by the diffracti<\nor inflection of light in the received theory. — See Brewst<\np. 95, The phenomena included under the title ' Epo\ntical Colours/ are generally known as the colours of th\nplates. They vary with the thickness of the film, and tl\ncolour seen by reflection always differs from that seen 1\ntransmission. The laws of these phenomena have be^\nthoroughly investigated. See Nobili, and Brewster, p. lOQ\n— S.F.\n\nThe colours produced by the transmission of polarisi\nlight through chrystalised mediums, were described 1\nGoethe, in his mode, subsequently to the publication of ti\ngeneral theory, under the name of Entoptic Colours. Si\nnote to Par. 485.\n\nNOTE L— Par. 150.\n\nWe have in this and the next paragraph the outline <\nGoethe's system. The examples that follow seem to e\ntablish the doctrine here laid down, but there are mar\ncases which it appears cannot be explained on such prii\nciples : hence, philosophers generally prefer the theory i\nabsorption, according to which it appears that certai\nmediums \" have the property of absorbing some of the con\n\nNOTES. 375\n\nponent ra^s of while li|^t, while they allow the passage of\nolhera.\"*\n\nWhether all the facts adduced bj Goethe — foi instance,\nthat recorded in Par. 172, are to be explained by this doc-\ntrine, we leave to the investigators of nature to determine.\nDr. Ediermann, in conversing with Goethe, thus described\nthe two leading phenomena (156, 158) as seen by him in the\nAlps. \" At a distance of eighteen or twenty miles at mid-\nday in bright sunshine, the snow appeared yellow or even\nreddish, while the dark parts of the mountain, free from\nsnow, were of the most decided blue. The appearances\ndid not surprise me, for I could have predicted that the\nmass of the interposed medium would give a deep yellow\ntone to the white snow, -but I was pleased lo witness the\neffect, since it so entirely contradicted the erroneous views of\nsome philosophers, who assert that the air has a blue-iinging\nquality. The observation, said Goethe, is of importance,\nand oontradicts the error you allude to completely.\"!\n\nThe same writer has some observatious to the same effect\non the colour of the Rhone at Geneva. A circumstance of\nan amusing nature which he relates in confirmation of\nGoethe's theory, deserves to be inserted. \" Here (at\nStrasbuig), passing by a shop, I saw a little glass bust of\nNapoleon, which, relieved as it was against the dark in-\n\n• See \" MUllei'i Element! of Phjuoli^,\" tnulaled from the Oennui bj\nWilliwn Baly, M.D. \" The lawa of ttbranitian,\" it hu been obeerred,\n\" have not been itudied irilb to much lUcceB ai Ihuie of other phencunenft of\nphyiieal optics, but aome eicellent obMnntioni on the nil^ect will be IiioimI\nin Henchell'i Tn»tiie oa Light in the BncyclopmliB Metropolitana, f III.\"\n\nt \" EckeniiBiin'g Qeaprlche n>it Ooetfae,\" vol. ii. p. 280. Leonardo da Vinci\nbad made precisely the uine obaervatioa. \" A distant monnlain irill appear\nof a moTc beautiful blue in proportion as it ii dark in colour. The illumiDed\nair, interposed belweeo the eye and the dark man, being thinner towards the\n•ammit of the mountain, will exhibit the darkness as a deeper bhie and vict\nMrirl.\"— TVaffatB dt//a Pillura, p. 143. Elsewhere—\" The air which in-\nlervenes between the eye alid dark mountains beootnc* blue ; but it does not\nbecome blue in (Iwforp) (he light part, and muih lew in (before) the portion\nthat I e covered with snow.\" — p. 244.\n\n376 NOTES.\n\nterior of the room, exhibited evcrj gradation of blue« f:\nmilky light blue to deep violet. I foresaw that the 1\nseen from within the shop with the light behind it, wc\npresent every degree of yellow, and I could not resist wi\ning in and addressing the owner, though perfectly unknc\nto me. My first glance was directed to the bust, in wh\nto my great joy, I saw at once the most brilliant colour\nthe warmer kind, from the palest yellow to dark rubj i\nI eagerly asked if I might be allowed to purchase the bi\nthe owner replied that he had only lately brought it ¥\nhim from Paris, from a similar attachment to the empc\nto that which I appeared to feel, but, as my ardour seen\nfar to surpass his, I deserved to possess it. So invalua\ndid this treasure seem in my eyes, that I could not h\nlooking at the good man with wonder as he put the bust i\nmy hands for a few franks. I sent it, together with a curit\nmedal which I had bought in Milan, as a present to Groet\nand when at Frankfort received the following letter fr\nhim/' The letter, which Dr. Eckermann gives entire, tl\nconcludes — \" When you return to Weimar you shall i\nthe bust in bright sunshine, and while the transpari\ncountenance exhibits a quiet blue,* the thick mass of 1\nbreast and epaulettes glows with every gradation of warm\nfrom the most powerful ruby-red downwards; and as 1\ngranite statue of Memnon uttered harmonious sounds, so 1\ndim glass image displays itself in the pomp of colours. T\nhero is victorious still in supporting the Farbenlehre.\"-!-'\n\nOne effect of Goethe's theory has been to invite the ;\ntention of scientific men to facts and appearances whi\nhad before been unnoticed or unexplained. To the abc\ncases may be added the very common, but very imports\nfact in painting, that a light warm colour, passed in a ser\n\n* This supposes either that tiie mass was considerably thicker, or that tl\nwas a (lark ground behind the head, and a light ground behind the rest of\nfigure.\n\nf «• Eckermann's GesprKche mit Goethe,\" vol. ii. p. 242.\n\nNOTES. ,177\n\ntransparent state over a <lark one, produces a cold, bluish\nbue, while the operation reversed, produces extreme warmth.\nOn the judicious application of both these effects, but espe-\ncially of the latter, the richness and brilliancy of the best-\ncoloured pictures greatly depends. The principle is to be\nrecognised in the productions of schools apparently oppo-\nsite in their methods. Thus the practice of leaving the\nground, through which a light colour is apparent, as a\nmeans of ensuring warmth and depth, is very common\namong the Dutch and Flemish painters. The Italians,\nagain, wlio preferred a solid under-punting, speak of in-\nternal light as tbe moat fascinating quality in colour. When\nthe ground is entirely covered by solid painting, as in the\nworks of some colourists, the warmest tints in shadows and\nreBections hare been found necessary to represent it. Thii\nwas the practice of Rembrandt frequently, and of Reynolds\nuniversally, but the glow of their general colour is still\nowing to its beii^ repeatedly or ultimately enriched on the\nabove principle. Lastly, the works of those masters who\nwere accustomed to paint on dark grounds are often heavy\nand opaque ; and even where this influence of tbe ground\nwas overcome, tbe effects of time must be constantly dimi-\nnishing tbe warmth of their colouring as the surface be-\ncomes rubbed and the dark ground more apparent through\nit. The practice of painting on dark grounds was intended\nby the Carracd to compel the students of their school to aim\nat the direct imitation of the model, and to acquire tbe use\nof the brush ; for the dark ground could only be overcome\nby very solid painting. The result answered their expecta-\ntions as far as dexterity of pencil was concerned, but the\nmethod was fatal to brilliancy of colour. An intelligent\nwriter of the seventeenth century* relates that Guido adopted\nbis extremely light style from seeing the rapid change in\nsome works of tbe Carracci soon after they were done It\n\n• Scanelli,\" Microcotmo della Piltmt,\" Ctmn*, 1657, p. 114.\n\n378 NOTES.\n\nis important^ however^ to remark, thai Guido's remedy i\nexternal rather than internal brilliancy; and it is evid\nthat 80 powerless a brightness as white paint can oolj i\nquire the splendour of light by great contrast, snd, ab\nall, by being seen through external darkness. The eec\nof Van Eyck and his contemporaries is always aaBiuned\nconsist in the vehicle (varnish or oils) he employed ; bu\nfar more important condition of the splendour of <x)iloiir\nthe works of those masters was the careful preservataon\ninternal light by painting thinly, but ultimately with gn\nforce, on white grounds. In some of the early Flemi\npictures in the Royal Gallery at Munich, it may be o\nserved, that wherever an alteration was made by the paint\nso that a light colour is painted over a dark one, the oolo\nis as opaque as in any of the more modem pictures whi'\nare generally contrasted with such works. No quality\nthe vehicle could prevent this opacity under such circnu\nstances; and on the other hand, provided the intern\nsplendour is by any means preserved, the vehicle is compai\ntively unimportant\n\nIt matters not (say the authorities on these points) wfa\nther the effect in question is attained by painting thin\nover the ground, in the manner of the early Flemish painte\nand sometimes of Rubens, or by painting a solid light pr\nparatiun to be afterwards toned to richness in the manner <\nthe Venetians. Among the mechanical causes of the clea\nncss of colours superposed on a light preparation may I\nmentioned that of careful grinding. All writers on art wt\nhave descended to practical details have insisted on thi\nFrom the appearance of some Venetian pictures it may t\nconjectured that the colours of the solid under-paintin\nwere sometimes less perfectly ground than the scumblin\ncolours (the light having to pass through the one and to b\nreflected from the other). The Flemish painters appear I\nhave used carefully-ground pigments universally. This i\nvery evident in Flemish copies from Raphael, which, thougl\n\nequall)' imputed with the originals, ore to be detected, among\nother indiotioiu, b; the finely -ground colour* employed\n\nNOTE M.— Par. 177-\n\nWithout eDtering further into the idenufic merila or de-\nmerits of this chapter on the \" Fint CUm of Dioptrical\nCnlours,\" it is to be obserred that several of the examples\ncorrespond with the observations of Leonardo da Vinci,\nand again with those of a much older authority, namely,\nAristotle. Goethe himself admits, and it has been remarked\nby others, that his theory, in many respects, closely resem-\nbles that of Aristotle: iadeed he confesses* that at one\ntime he had an intention of merely paraphrasing that philo-\nBt^ber's Treatise on Colours, f\n\nWe have already remarked (Note on par. 150) that\nGoethe's notion with regard to the production of warm\ncolours, by the interpoution of dark transparent mediums\nbefore a light ground, agrees with the practice of the best\nschools in coloming ; and it is not impossible that the same\nreasons which may make this part of the doctrine generally\nacceptable to artists now, may have recommended the very\nsimilar theory uf Aristotle to the painters of the fifteenth\nand sixteenth centuries : at all events, it appears that the\nandent theory was known to those painters.\n\nIt is unnecessary to dwell on. the fact that the doctrines\nof Aristotle were enthusiastically embraced and generally\ninculcated at the period in question ;^ but it has not been\n\n• \"OMchicbtadec FsrbcnMue,\" in llie \" NschgeUnene Wuk>.\" Cotts,\n\nf The IraatUe in qoHtion ii ucribnl tiy Oocthc to Tbeophrmrtua, but it ia\nincluded in moat editioM of Aibtotla, toA even aUributeil to him in tlioM\nwhich eonlun ths trotki aT Loth philowphan ; tot inituice, in the Aldioe\nPrincupt edition, 1496. Calcignini uji, the troktiu ii mads op of two Kpa-\nlats wotki on the nibject, both by Ariitotle.\n\n\\ His ulhoritj Henu to haie been equally greaX do wlgecli cmneeted\nwith the phenomena of vittion : the ItsJiaa tnoalatot of ■ iMtia treatiH,bf\nPoitiua, on ihe ittuctuie and coloun dC the eye, Ibui openi hii dedication to\nthe Cardinal Eicole Qotiioga, of Mantua: — \"Oiande ami quan iofiinto ^\n\n380 NOTES.\n\nobserved that the Italian writers who translated, p\nphrased, and commented on AristotIe*s Treatise on Col\nin particular, were in several instances the personal fri<\nof distinguished painters. Celio Calcagnini* had the hig\nadmiration for Raphael ; Lodo>ico Dolcef was the eul<\nof Titian ; Fortius,]; whose amicable relations i¥ith the\nrentine painters may be inferred from various circumstaE\nlectured at Florence on the Aristotelian doctrines earl\nthe sixteenth century. The Italian translations were h\nbut still prove that these studies were undertaken with\nference to the arts, for one of them is dedicated to\npainter Cigoli.§\n\nPobligo che ba il mondo con quel pid divino che umano spirito di A]\ntUe.\"\n\n* In a letter to Zi^ler the mathematician, Calcagnioi speaka of Ra;\nas \" the first of painters in the theory as well as in the practice of his i\nThis expression may, however, have had reference to a remarkable ein\nstance mentioned in the same letter, namely, that Raphael entertained\nlearned Fabius of Ravenna as a constant guest, and employed him to tram\nVitruvius into Italian. This MS. translation, with marginal notes, wri\nby Raphael, is now in the library at Munich. *' Passavant, Rafael von Urbu\n\nf Lodovico Dolce's Treatise on Colours (1565) is in the form of a dialoj\nlike his \" Aretino.\" The abridged theory' of Aristotle is followed by a tn\nlation of the Treatise of Antonius Thylesius on Colours ; this is adapted to\nsame colloquial form, and the author is not acknowledged : the book e\nwith an absurd catalogue of emblams. The ** Somma della Filoeofia d'A\ntotile,*' published earlier by the same author, is a very careless perfonnanc\n\nI A Latin translation of Aristotle's Treatise on Colours, with comments\nSimon Fortius, was first published, according to Goethe, at Naples in 15\nIn a later Florentine edition, 1548, dedicated to Cosmo I., Fortius alludes\nhis having lectured at an earlier period in Florence on the doctrines of A\ntotle, at which time he translated the treatise in question. Another La\ntranslation, with notes, was published later in the same century at Padui\n** Emanuele Marguino Interprete :\" but by far the clearest view of the Arii\ntelian theory is to be found in the treatise of Antonio Vidi Scarmiglion<\nFuligno Q* De Coloribus,\" Marpurgi, 1591). It is dedicated to the Empe\nRudolph II. Of all the paraphrases of the ancient doctrine this comes ueai\nto the system of Goethe ; but neither this nor any other of the works allu^\nto throughout this Note are mentioned by the author in his History of l\nDoctrine of Colours, except that of Fortius.\n\n^ An earlier Italian translation ap]ieared in Rome, 1535. See ** Argela\nBiblioteca degli Volgariisatori.\"\n\nNOTES. 381\n\nThe writers on art, from Leon Batista Alberti to Bor-\ngliini, without mentioning later authorities, either lacitlj\ncoindde with the Aristotelian doctrine, or openly profess\nto explain it. It is true this is not always done in the\nclearest manner, and some of these writers mifht say with\nLodovico Dolce, \" I speak of colours, not as a punter, for\nthat would be the province of the divine Titian,\"\n\nLeonardo da Vinci in his writings, as in everything else,\nappears as an original genius. He now and then alludes\ngenerally to opinions of \" philosophers,\" but he quotes no\nauthority ancient or modem. Nevertheless, a passage on\nthe nature of colours, particularly where he speaks of the\ncolours of the elements, appears to be copied from lieon\nBattista Alberti,* and from the mode in which some of\nLeonardo's propositions are staled, it has been supposed f\nthat he had been acrustomed at Florence to the form of the\nAristotelian philosophy. At all events, some of the moat\nimportant of his observations respecting light and colours,\nhave a great analogy with those contained in the treatise in\nquestion. The following examples will be sufficient to\nprove this coincidence ; the corresponding passages in\nGoethe are indicated, as usual, by the numbers of the para-\ngraphs; the references to Leonardo's treatise are given at\nthe bottom of the page.\n\nAristotle.\n'* A vivid and brilliant red appears when the weak rays of\nthe sun are tempered by subdued and shadowy white.\" —\n\nLeonardo.\n\" The air which is between the sun and the earth at sun-\n\n• \" Delia Piltura e delU Statu*,\" Lib. 1, p. 16, Milan fdilion, 1804. Com-\nparowith tho \"Tcattato dell& Pittura,\" p. 141. Othei pobia of reiemblance\n■ri to be met vith. The notion of certain colour* appropriated to the four\n•lomenis, oecum in Arislatle, and ii indeed attiibuled to older writer*.\n\nt See the notet to the Roman editioQ of the \"Trattato della Pittura.\"\n\n382 NOTES.\n\nrise or sun-set, always invests what is beyond it mor\nany other (higher) portion of the air : this is becaui\nwhiter.\"*\n\nA bright object loses its whiteness in proportion\ndistance from the eye much more when it is illumina^\nthe sun, for it partakes of the colour of the sun minglo\nthe colour (tempered by the mass) of the air interpose\ntween the eye and the brightness-f\n\nAristotle.\n\n*' If light is overspread with much obscurity, a red c\nappears ; if the light is brilliant and vivid, this red cb\nto a flame-colour.\"]: — 150, l60.\n\nLeonardo.\n\n'* This (the effect of transparent colours on vs\ngrounds) is evident in smoke, which is blue when\nagainst black, but when it is opposed to the (light)\nsky, it appears brownish and reddening.'* §\n\nAristotle.\n\n'< White surfaces as a ground for colours, have the\nof making the pigments|| appear in greater splendou\n594, 902.\n\n♦ Page 237.\nt Pago 301\n\nI lu the Treatise De Igne^ by Theophrastus, we fiiid the same notk\npressed : \" Brightness (t« Xivmv) seen through a dark coloured na\n(}tm t3 ftiXmwi) appears red ; as the sun seen through smoke or soot :\nthe coal is redder than the flame.\" Scarmiglione, from whom Kircher\nto have copied, observes: — ^''Itaque color realis est lux opaca; lice\nplurimis appareutiis colligere. Luna euim in magnft solis t'cUpsi rubr\nspicitur, quia tenebris lux prspeditur ac veluti tegitur.\" — D« Coioribm\n\ni Page 122.\n\nII T« JLf^n : translated Jl€0rtt by Caleaguiui and the rest, by Ooetli\nBfuthe, the bloom. That the word sometimes signified pigments is suA\napparent from the following passage of Suidas (quoted by Emeric David,\ncours llii^riques sur la Peinture Modenie'') iydir* si»«r^»iipiMu, •«•» ^^tf\n\nLeonardo.\n\n\" To exhibit colours in their beauty, the whitest gronnd\n■bould be prepared. I apeak of colours that are (more or\nless) tranaparent.\"*\n\nAristotle.\n\n\"The air near ns appears colourless j but when seen in\ndepth, owing to its thinness it appears blue;f for where the\nlight is deficient (beyond it), the air is affected by the dark-\nness and appears blue : in a very accumulated state, how-\never, it appears, as is the case with water, quite white.\" —\n155. 158.\n\nLeonardo.\n\n\" The blue of the atmosphere is owing to the mass of\nilluminated air interposed between the darkness above and\nthe earth. The air in itself has no colour, but assumes\nqualities according to the nature of the objects which are\nbeyond it. The blue of the atmosphere will be the more\nintense in proportion to the degree of darkness beyond it :\"\nelsewhere — \" if the lur had not darkness beyond it, it would\nbe white.\"!\n\nAristotle.\n\n\" We see no colour in its pure state, but every hue is\nvariously intermingled with others: even when it is unin-\nfluenced by other colours, the effect of light and shade\nmodifies it in various ways, so that it undergoes alterations\nand appears unlike itself. Thus, bodies seen in shade or in\n\nfixti ami tKi tfulni. VariupignUDtuoTiut«,ut eeruHl,Aia>,<taliuunii]ib(u.\n(Suid. in Toc. '^^!aSlr|titm.) A paml prapuad Tor punting, with a while\ngnund conwtidaMd with wu,uk1 p«rha]Mmutie,wufb(U>d in Uvrenlaaenm.\n\n• P*gii 114.\n\nif Hirvra. \" But when (em in depth, it appMum (even) in itn Dssnat colutu,\nblue, owii^ to it* thinnea.\" The L«hD intcipietatioM Tmiy verjr much\nthroughout. \"Hie point which ii ehiaflj importwil ia howerer pUn (oough,\nvii. thftt daikncn Man throogh ■ light madima ii bhl*.\n\n• Pogfl 136—130.\n\n382 NOTES.\n\nrise or sun-set, always invests what is beyond it more tl\nany other (higher) portion of the air : this is because i\nwhiter.\"*\n\nA bright object loses its whiteness in proportion to\ndistance from the eye much more when it is illuminated\nthe sun, for it partakes of the colour of the sun mingled k\nthe colour (tempered by the mass) of the air interposed I\ntween the eye and the ln%htness.f\n\nAristotle.\n\n'* If light is overspread with much obscurity, a red coli\nappears ; if the light is brilliant and vivid, this red chan\nto a flame-colour.\"]; — 150, 160.\n\nLeonardo.\n\n'' This (the effect of transparent colours on varii\ngrounds) is evident in smoke, which is blue when m\nagainst black, but when it is opposed to the (li^ht) b\nsky, it appears brownish and reddening.'* §\n\nAristotle.\n\n*' White surfaces as a ground for colours, have the efi\nof making the pigments|| appear in greater splendour/'\n594, 902.\n\n* Page 237.\n\nt Page 301\n\nI lu the Treatise De Jgne, by Theophrastus, we find the same notioD t\npressed : '* Brightness (r« Xivmv) seen through a dark coloured medii\n(X« t5 f»i>MtH) appears red ; as the sun seen through smoke or soot : hei\nthe coal is redder than the flame.'* Scarmiglione, from whom Kircher see\nto have copied, obaerves : — \" Itaque color realis est lux opaca ; licet id\nplurimis apparentiis colligere. Luna euim in magnft solis eclipai rubra cc\nspicitur, quia tenebris lux praepeditur ac veluti tegitur.'* — D« Coiarihmtm\n\n§ Page 122.\n\nI) T« 4tvSff : translated Jlvrei by Calcaguiul and the rest, by Goethe, 4\nBfdihtf the bloom. That the word sometimes signified pigments it suflfeieul\napparent from the following passage of Suidas (quoted by Emeric David, ** Di\ncours Uistoriques sur la Peinture Modenie'') ir^ir* si»«r^M|]MMu, •mp i^y^^A\n\nLeonardo.\n\n\" To exhibit colours in their beauty, the whitest ground\nshould be prepared. I speak of colours that are (more or\nless) transparent.\"*\n\nAristotle.\n\n\" The air near us appears colourless ; but when seen in\ndepth, owing to its thinness it appears blue ;f for where the\nlight is defident (beyond it), the ur is affected bjr the dark-\nness and appears blue : in a very accumulated state, how-\never, it appears, as is the case with water, quite white.\" —\n155, 158.\n\nLeonardo.\n\n\" The blue of the atmosphere is owing to the mass of\nilluminated air interposed between the darkness above and\nthe earth. The ^ in itself has no colour, but assumes\nqnalities according to the nature of the objects which are\nbeyond it. The blue of the atmosphere will be the more\nintense in proportion to the d^ree of darkness beyond it :\"\nelsewhere^\" if the air bad not darkness bey<md it, it would\nbe white. \"J\n\nAristotle.\n\n\" We see no colour in its pure state, but every hue is\nvariously intermingled with others: even when it is unin-\nfluenced by other colours, the effect of light and shade\nmodifies it in various ways, so that it undergoes alterations\nand appears unlike itself. Thus, bodies seen in shade or in\n\nfimii ««3 TiTf j^M/tjf. Vaiii> pk^nuDtu (iniAtv,ut crnmif luco, vt aIUi timilibui.\n(Suid. in roc. 'i{a>9iry>i>iu.) A paoel prvpued for painting, witli a vhite\nground coiuolidAted witL wax, and peihqaiiiaMic,wai found in HsrculaneiuD.\n• Page 114.\n\nt 'E> ditu h iuiftii/tlwtli iyytrirK fmnrmi n Xf^l\"''\" ■MHuifll U t*>\nifminrm, \" But when teen in deptb, it appun (even) in ita uoaiint coluur,\nblue, owing to iu thinucH.\" The l^tin interpretatioiM vaxj very much\nttiDughout. The point which ii chiefly impoiluit ii however plain enougb,\nvii. that darkncH leen through a light mediuin ii Uue-\n\n1 Page 136-430.\n\n386 NOTES.\n\nfor be seems to consider that blue may be produced bj\nactual mixture of black and white^ provided tbey are pv\nThe ancient author, however, explains himself on this ]\nas follows — '* We must not attempt to make our obsi\ntions on these effects by mixing colours as painters mix tl\nbut by remarking the appearances as produced by the\nof light mingling with each other/'f\n\nWhen we consider that Leonardo's Treatise profess^\nembrace the subject of imitation in painting, and that I\ntotle*s briefly examines the physical nature and appean\nof colours, it must be admitted that the latter sustains\nabove comparison with advantage ; and it is somewhat\ntraordinary that observations indicating so refined a kn\nledge of nature, as regards the picturesque, should not I\nbeen taken into the account, for such appears to be\nfact, in the various opinions and conjectures that have \\\nexpressed from time to time on the painting of the Gre\nThe treatise in question must have been written w\nApelles painted, or immediately before; and as a pi\n\n(Somma della Filos. d'AriRt.) ; but elsewhere, p. 306, Lomano agrees\nAlberti. AriMtotle seems to have misled the two first, for after saying t\narc seven colours, he appears only to mention six : he says — ^'^ There are s\ncolours, if brown is to be considered efjuivalent to black, which seeniA rea\nable. Yellow, again, may be said to be a modification of white. Befi\nthese we find red, purple, f^een, and blue.\" — De Sentu et Sen»i/i. Perl\nit is in accordance with this passage that Leonardo da Vinci reckona c\ncolours. — TrattatOy p. 126.\n\n♦ Page 122, 142, 237.\n\nf On the authority of this explanation the word ^iXa* has 8ometiin€>8 1\ntranslated in the foregoing extracts o6«ei/ri/y, darkness.\n\nRafTaello Borghini, in his attempt to destrribe the doctrine of Aristotle i\na view to painting, obser^'es — \" There are two principles which concur in\nproduction of colour, namely, light and transparence.\" But he soon loses\nclue to the l>est part of the ancient theory, and when he has to speak of\nderivation of colours from white and black, he evidently understands it\nmere atomic sense, and adds — '** I shall not at present pursue the opinio;\nAristotle, who assumes black and white as principal colours, and considers\nthe rest as intermediate between them.\" — // RiposOy 1. ii. Accordingly, 1\nLodovico Dolce, he j»rooeed» to a subject where he was more at home, naui<\nthe symlmlical meaning of colours.\n\nNOTES. 387\n\nthat Ariatotle'a remarks on the effect of Kini'traDspareiit\nmediums were not lost on the artists of his time, the follow-\ning passage from Pliny is subjoined, for, though it is well\nknown, it acquires additional interest from the loregoii^\nextracts.\n\n\" He (Apelles) passed a dark colour over his pictures\nwhen finished, so thin that it increased the splendour of the\ntints, while it protected the surface from dust and dirt : it\ncould only be seen on looking into the picture. The effect\nof this operation, judiciously managed, was to prevent the\ncolours from being too glaring, and to give the spectator the\nimpression of looking through a transparent crystal. At\nthe same time it seemed almost imperceptibly to add a\ncert^n dignity of tone to colours that were too florid.\"\n\" This,\" says Reynolds, \" is a true and artist-like descrip-\ntion of glazing or scumbling, such as was practised by\nTitian and the rest of the Venetian painters.\"\n\nThe account of Pliny has, in this instance, internal evi-\ndence of truth, but it is fully confirmed by the following\npassage in Aristotle : — \" Another mode in wluch the effect\nof colours is exhibited is when they appear through each\nother, as painters employ them when they glaze (iwaKei-\n_^tTis)* a (dark) colour over a lighter one ; just as the sun,\nwhich is in itself white, assumes a red colour when seen\nthrough darkness and smoke. This operation also ensures\na variety of colours, for there will be a certain ratio between\nthose which are on the surface and those which are in\ndepth.\" — De SeJtsu et Sensili.\n\nAristotle's notion respecting the derivation of colours\nfrom white and black may perhaps be illustrated by the\nfollowing opinion on the very similar theory of Goethe.\n\n\"Goethe and Seebeck regard colour as resulting from\nthe mixture of white and black, and ascribe to the different\n\n• Tliw word is only strielly applied to unctuous subttancei, and mnj roiiflnn\ntbe viewE of fhoH* writera who ha-ve conjectnred th&( wpboltum wu > chief\niiiin'clicTil ill tbe alrnnunlinii of the ancienta.\n\n2 c 2\n\n388 NOTES.\n\ncolours a quality of darkness ((txie^ov), by the difierent d\ng^ees of which they are distinguished, passing from white\nblack through the gradations of yellow, orange, red, vioL\nand blue, while green appears to be intermediate again fa\ntween yellow and blue. This remark, though it has i\ninfluence in weakening the theory of colours proposed 1\nNewton, is certainly correct , having been confirmed expei\nmentally by the researches of Herschell, who ascertains\nthe relative intensity of the different coloured rays by illi\nminating objects under the microscope by their means, &c\n\n** Another certain proof of the difference in brightness <\nthe different coloured rays is afforded by the phenomena i\nocular spectra. If, after gazing at the sun, the eyes ai\nclosed so as to exclude the light, the image of the sun aj\npears at first as a luminous or white spectrum upon a dar\nground, but it gradually passes through the series of coloui\nto black, that is to say, until it can no longer be distic\nguished from the dark field of vision ; and the coloui\nwhich it assumes are successively those intermediate be\ntween white and black in the order of their illuminatin;\npower or brightness, namely, yellow, orange, red, violet\nand blue. If, on the other hand, after looking for somi\ntime at the sun we turn our eyes towards a white surface\nthe image of the sun is seen at first as a black spectrun\nupon the white surface, and gradually passes through thi\ndifferent colours from the darkest to the lightest, and a\nlast becomes white, so that it can no longer be distinguishec\nfrom the white surface \"* — See par. 40, 44.\n\nIt is not impossible that Aristotle's enumeration of th<\ncolours may have been derived from, or confirmed by, this\nvery experiment. Speaking of the after-image of a>lours\nhe says, \" The impression not only exists in the sensorium\nin the act of perceiving, but remains when the organ is at\nrest. Thus if we look long and intently on any object,\n\n* \" Elements of Physiologj,\" by J. Muller, M.D., translated from the Ger-\nman by William Baly, M.D. London, 1839.\n\nwhen we chEn^ the direction of the eyes a responding\ncolour follows. If we look at the sun, or any other very\nbright object, and afterwards shut our eyes, we shall, as if\nin ordinary vision, first see a colour of the same kind ; this\nwill presently he changed to a red colour, then to purple,\nand so on till it ends in black and disappears.\" — Oe Jnsom-\nniU.\n\nNOTE N.— Par. 246.\n'• The appearance of white in the centre, according to\nthe Newtonian theory, arises from each line of rays forming\nits own spectrum. These spectra, superposing each other\non all the middle part, leave uncorrected (unneuCraliBetl)\ncolours only at the two edges.\" — S. F.*\n\nNOTE O.— Par. 852.\nThese experiments with grey objects, which exhibit dif-\nferent colours as they are on dark or light grounds, were\nsu^ested, Goethe tells us, by an observation of Antonius\nLucas, of Liittich, one of Newton's opponents, and, in the\nopinion of the author, one of the few who made any well-\nfounded objections. Lucas remarks, that the sun acts\nmerely as a circumscribed image in the prismatic experi-\nments, and that if the same sun Iiail a lighter background\nthan itself, the colours of the prism would be reversed.\nThus in Goethe's experiments, when the grey disk is on a\ndark ground, it is edged with blue on being magni6ed;\nwhen on a light ground it is edged with yellow. Goethe\nacknowledges that Lucas had in some measure anticipated\nhis own theory. — Vol. ii. p. 440.\n\nNOTE P.—Par. 284.\nThe earnestness and pertinacity with which Goethe in-\n\n• This WBB objected to Goelbe obeu hit \" BeytrUge itir Optik\" Hnt ap-\npeaieil ; he answered (be objecliou by a coloured diagram in the plain to (he\n\" FaTbenUhre i\" in this he undertokn to (bow that the RMUinnl gradual\n■' roirecf ion\" of the voIouD would produce lenilta different from the ulual\nappearance in iwiture.\n\n390 NOTES.\n\nlisted that the different colours are not subject to differe\ndegrees of refrangibility are at least calculated to prove tl\nbe was himself convinced on the subject, and, however c\ntraordinary it may seem, his conviction appears to have be\nthe result of infinite experiments and the fullest oeular cr\ndence. He returns to the question in the oontroversi\ndivision of his work, in the historical part, and again in t\ndescription of the plates. In the first he endeavours\nshow that Newton*s experiment with the blue and red pap\ndepends entirely on the colours being so contrived as\nappear elongated or curtailed by the prismatic bordei\n\" If,*' he says, \" we take a light-blue instead of a dark on\nthe illusion (in the latter case) is at once evident Accor<\ning to the Newtonian theory the yellow-red (red) is tl\nleast refrangible colour, the violet the most refrangibl\nWhy, then, does Newton place a blue paper instead of\nviolet next the red ? If the fact were as he states it^ tl\ndifference in the refrangibility of the yellow-red and viol\nwould be greater than in the case of the yellow-red an\nblue. But here comes in the circumstance that a violi\npaper conceals the prismatic borders less than a dark-blu\npaper, as every observer may now easily convince himself,\n&c. — Polemischer Theil, par. 45. Desaguliers, in repeal\ning the experiment, confessed that if the ground of th\ncolours was not black, the effect did not take place so well\nGoethe adds, \"not only not so well, but not at all.\" — His\ntorischer Theil, p. 459- Lucas of Liittich, one of Newton'\nfirst opponents, denied that two differently- coloured silks ar\ndifferent in distinctness when seen in the microscope\nAnother experiment proposed by him, to show the un\nsoundness of the doctrine of various refrangibility, was th(\nfollowing: — Let a tin plate painted with the prismatic co\nlours in stripes be placed in an empty cubical vessel, S4\nthat from the spectator's point of view the colours may hi\njust hidden by the rim. On pouring water into this vessel\nall the colours become visible in the same degree ; whereas\nit was contended, if the Newtonian doctrine were true, some\n\nNOTES. 301\n\ncolours would be apparent before otbera. — Histonscher\nTheil, p. 434.\n\nSuch are the arguments and experiments adduced by\nGoethe on this subject ; they have all probably been an-\nanered. Id his analysis of Newton's celebrated Experi-\ntnaifum CrucU, he shows again that by reversing the pris-\nmatic colours (refracting a dark instead of a light object),\nthe colours that are the most refrangible in Newton's expe-\nriment become the least so, and vice vend.\n\nWithout reference to this objection, it is now admitted\nthat \"the difference of colour is not a test of difference of\nrefrangibility, and the conclusion deduced by Newton is no\nlonger admissible as a general truth, that to the same de-\ngree of refrangibility ever belongs the same colour, and to\nthe same colour ever belongs the same degree of refrangi-\nbility.\" — Brewster's Optics, p. 72.\n\nNOTE Q.— Par. 387-\nWith the exceptiun of two very inconclusive letters to\nSulpice Boisseree, and some incidental observations in the\nconclusion of the historical portion under the bead of eii-\nloptic colours, Goetbe never returned to the rainbow.\nAmong the plates he gave the diagram of Anlonius de Do-\nminis. An interesting chapter on haloa, parhelia, and\nparaselene, will be found in Brewster's Optics, p. 270.\n\nNOTE R— Par. 478.\n\nThe most complete exhibition of the colourii^ or mant-\nling of metals was attained by the late Cav. Nobili, pro-\nfessor of physical science in Florence. The general mode\nin which these colours are produced is thus explained by\nhim:* —\n\n\" A point of platinum is placed vertically at the distance\nof about hair a line above a lamina of the same metal laid\n\n• 8re ■• Mrniarir «i OHwnmioni, wiilc K hieiiilc del Cav. Pttd'mwr No-\n\n392 NOTES.\n\nhorizontally at the bottom of a vessel of glass or porcela\nInto this vessel a solution of acetate of lead is poured so\nto cover not only the lamina of platinum^ but two or thr\nlines of the point as well. Lastly, the point is put in cx>i\nmunication with the negative pole of a battery^ and ti\nlamina with the positive pole. At the moment in whii\nthe circuit is completed a series of coloured rings is pr\nduced on the lamina under the point similar to those o1\nserved by Newton in lenses pressed together.\"\n\nThe scale of colours thus produced corresponds ve:\nnearly with that observed by Newton and others in thi\nplates and films^ but it is fuller, for it extends to fortj-foi\ntints. The following list, as given by Nobili^ is divide\nby him into four series to agree with those of Newton : tl\nnumbers in brackets are those of Newton^s scale. Tt\nIiahan terms are untranslated, because the colours in son\ncases present very delicate transitions.*\n\nFirst Series,\n1 Biondo argentine (4).f 6. Fulvo acceso.\n\n2. Biondo. 7. Rosso di rame (6).\n\n3. Biondo d'oro. 8. Ocria.\n\n4. Biondo acceso (5). 9- Ocria violacea.\n\n5. Fulvo. 10. Rosso violaceo (7).\n\nSecond Series,\n\n1 1. Violetto (8). 20. Giallo acceso.\n\n12. Indaco y^lO). 21. Giallo-rancio.\n\n13. Blu carico. 22. Rancio (13).\n\n14. Blu. 23. Rancio-rossiccio.\n\n15. Blu chiaro (11). 24. Rancio-rosso.\n\n16. Celeste. 25. Rosso- rancio.\n\n17- Celeste giallognolo. 2G. Lacca-rancia (14).\n\n18. Giallo chiarissimo (12). 27. Lacca.\n\n19. Giallo. 28. Lacca accesa (15).\n\n* The colours in some of tlie compound terms are in a manner mutuallj\nueutraliaing ; such terms might, no doubt, be amended.\n\nt The three first numbers in Newton's scale are black, blue, and white.\n\nJ%ird Series.\n\n29. Lacca-purpurea (16). 34. Verde-giallo (20).\n\n30. Lacca-turchiniccia(17). 35. Verde-rancio.\n\n31. Porpora'Vcrdogaola(l8). 36. Rancio-verde (21).\n\n32. Verde (19). 37. Rancio-roseo.\n\n33. Verde giallognolo. 38. Lacca-rosea (22).\n\nFoarth Series.\n\n39. Lacca-violacea (24). 43. Verde-giallo roMiccio\n\n40. Violaceo-verd<^:nolo(25). (28).\n\n41. Verde (26). 44. Lacca-rosea (30).\n\n42. Verde-giallo («7).\n\n\" These tints,\" Professor Nobili observes, \" are disposed\naccording to the order of the thin mantlings which occasion\nthem ; the colour of the thinnest film is numbered 1 ; then\nfollow in order those produced by a gradual thickening of\nthe medium. I cannot deceive myself in this arrangement,\nfor the thin films which produce the colours are all applied\nwith the same electro-chemical process. The battery, the\nsolution, the distances, &c., are always the same; the only\ndilference is the time the effect is suffered to last. Thia\nis a mere instant for the colour of No. I, a little longer for\nNo. S, and so on, increasing for the succeeding numbers.\nOther criterion*, however, are not wanting to ascertain the\nplace to which each tint belongs.\"\n\nThe scale difTers from that of Newton, inasmuch as there\nia no blue in Nobili's first series and no green in the se-\ncond: green only appears in the third and fourth series.\n\" The first series, ' says the Professor, \" is remarkable for\nthe fire and metallic appearance of its tints, the second for\nclearness and brilliancy, the third and fourth for force and\nrichness.\" The fourth, he observes, has the qualities of\nthe third in a somewhat lesser degree, but the two greens\nare very nearly alike.\n\nIt is to be observed, that red and green are the principal\n\n394 NOTES.\n\ningredients in the third and fourth series> blue and yell\nin the second and first.\n\nNOTE S.— Par. 485.\n\nA chapter on entoptic colours, contained in the sup}\nment to Goethe*s works, was translated with the intent\nof inserting it among the notes, but on the i^bole it ^\nthought most advisable to omit it. Like many other pi\nof the \" Doctrine of Colours\" it might have served a\nspecimen of what may be achieved by accurate observat\nunassisted by a mathematical foundation. The wh\ntheory of the polarization of light has, however, been\nfully investigated since Goethe*s time, that the chapter\nquestion would probably have been found to contain v\nlittle to interest scientific readers, for whom it seems chic\nto have been intended. One observation occurs in it wh\nindeed has more reference to the arts ; in order to mi\nthis intelligible, the leading experiment must be first\nscribed, and for this purpose the following extracts n\nserve.\n\n3*\n\n'* The experiment, in its simplest form, is to be made\nfollows : — let a tolerably thick piece of plate-glass be\ninto several squares of an inch and a half; let these\nheated to a red heat and then suddenly cooled. T\nsquares of glass which do not split in this operation are n\nfit to produce the entoptic colours.\n\n\"In our mode of exhibiting the phenomenon, the c\nserver is, above all, to betake himself, with his apparal\nto the open air. All dark rooms, all small apertures (foi\n\n* Tiie numbers, as usual, indicate the corresponding paragraphs in\noriginal.\n\nmina exigvia),* are again to be given np. A pure, cloud-\nless sky is the suurcc whence we are to derive a satisfactory\ninsight into these appearances.\n\n\" The atmosphere being clear, let the observer lay the\nsquares above described on a black surface, so placing them\nthat two sides may be parallel with the plane of vision.\nWhen the sun is low, let him hold the squares so as to re-\nflect to the eye that portion of the sky opposite to the sun,\nand he will then perceive four dark points in the four cor-\nners of a light space. If, after this, he turn towards the\nquarters of the sky at right angles with that where his first\nobservation was made, he will see four bright points on a\ndark ground : between the two regions the figures appear\nto fluctuate.\n\n\" From this simple reflection we now proceed to another,\nwhich, but little more complicated, exhibits the appearance\nmuch more distinctly. A solid cube of glass, or in its stead\na cube composed of several plates, is placed on a black\nmirror, or held a little inclined above it, at aim-rise or sun-\nset. The reflection of the sky being now suffered to fall\nthrough the cube on the mirror, the appearance above de-\nscribed will appear more distinctly. The reflection of the\nsky opposite to the sun presents four dark points on a light\nground; the two lateral portions of the sky present the\ncontrary appearance, namely, four light points on a dark\nground. The space not occupied by the corner points ap-\npears in the first case as a white cross, in the other as a\nblack cross, expressions hereafter employed in describing\nthe phenomena. Before sun-rise or after sun-set, in a very\n\n• In (he historical part, Ouetbc hjn lu apaat of «o many fullowers of New-\nton wlin br);ii> their statemenfH with '-Si per foranien eii^um,\" Ibat the\nleim i« a wtt of hy-woid with him.\n\n396 NOTES.\n\nsubdued lights the white cross appears on the side <\nsun also.*\n\n\" We thus conclude that the direct reflection of tl\nproduces a light figure, which we call a white cross\noblique reflection gives a dark figure, which we call a\ncross. If we make the experiment all round the si\nshall find that a fluctuation takes place in the intenn\nregions,\"\n\nWe pass over a variety of observations on the mo^\nexhibiting this phenomenon, the natural transparent\nstances which exhibit it best, and the detail of the o\nseen within f them, and proceed to an instance wher\nauthor was enabled to distinguish the <* direct'\" fron\n\"oblique\" reflection by means of the entoptic appa\nin a painter's study.\n\n'< An excellent artist, unfortunately too soon taken\nus, Ferdinand Jagemann, who, with other qualifications\na fine eye for light and shade^ colour and keeping^^ had\nhimself a painting-room for large as well as small wt\nThe single high window was to the north, facing the i\nopen sky, and it was thought that all necessary requi\nhad been sufliciently attended to.\n\n\" But after our friend had worked for some time, it\npeared to him, in painting portraits, that the faces he coj\nwere not equally well lighted at all hours of the day,\nyet his sitters always occupied the same place^ and the\nrenity of the atmosphere was unaltered.\n\n*' The variations of the favourable and unfavourable li\nhad their periods during the day. Early in the mom\nthe light appeared most unpleasantly grey and unsatisi\n\n♦ At mid-day on the 24th of June the author ub«eryed the white cro«i\nfleeted from every part of the horizon. At a certain distance from the i\ncorresponding, he wipiwaes, with the extent of haloR, the black crow appea\n\nf Whence the term entoptic.\n\nNOTES. 397\n\ntory ; it became better, till at lait, about an hour before\nnoon, the objects had acquired a totally different appear-\nance. Everything presented itself to the eye of the artist\nin its greatest perfection, as he would most wish to transfer\nit to canvas. In the afternoon this beautiful appearance\nvanished — the light became worse, even in the brightest\nday, without any change having taken place in the atmo-\nsphere.\n\n\" As soon as I heard of this circumstance, I at once con-\nnected it in my own mind with the phenomena which I had\nbeen so long observing, and hastened to prove, by a phy-\nsical experiment, what a clear-sighted artist had discovered\nentirely of himself, to his own surprise and astonishment.\n\n\" I had the second* entoptJc apparatus brought to the\n■pot, and the effect on this was what might be conjectured\nfrom the above statement. At mid-day, when the artist\n■aw bis model best lighted, the north, direct reflection gave\nt))e white cross ; in the morning and evening, on the other\nhand, when the unfavourable oblique light was so unplea-\nsant to him, the cube showed the black cross; in the inter-\nmediate hours the state of transition was apparent.\"\n\nThe author proceeds to recal to his memory instances\nwhere works of art had struck him by the beauty of their\nappearance owing to the light coming from the quarter op-\nposite the sun, in \" direct reflection,\" and adds, \" Since these\ndecided effects are thus traceable to their cause, the friends\nof art, in looking at and exhibiting pictures, may enhance\nthe enjoyment to themselves and others by attending to a\nfortunate reflection.\"\n\n* Before ileacribed : (he aulhoi detcribci eevetal athen moie or leu com-\nplicated, uid niggeiti a portable one. \" SucL pUlee, which need only b« on\ninch and ■ quactei square, placed an each other to form a cube, might be >et\nId a bran cane, open above and below. Al one end of thi> cage a black mir-\nror with a hiiiKe. acting like a cover, might be fastened. We recommend\nthii aimpte apparatus, wilb which the principal and original experiment may\nbe readily iDade. With this we could, in (he longest days, belter deline (he\ncircle round the sun wbere the black cross appears,\" &c.\n\n398 NOTES.\n\nNOTE T.— Par. 496.\n\n\" Since Goethe wrote, all the earths have been dec\nposed, and have been shown to be metallic bases uo\nwith oxygen ; but this does not invalidate his statement\nS.F.\n\nNOTE U— Par. 502.\n\nThe cold nature of black and its affinity to blue\nassumed by the author throughout ; if the quality is opai\nand consequently greyish, such an affinity is obvious,\nin many fine pictures, intense black seems to be consid<\nas the last effect of heat, and in accompanying* crimson\norange may be said rather to present a difference of dq\nthan a difference of kind. In looking at the great pic\nof the globe, we find this last result produced in dim\nwhere the sun has greatest power, as we find it the im:\ndiate effect of fire. The light parts of black animals\noften of a mellow colour ; the spots and stripes on s]\nand shells are generally surrounded by a warm hue^\nare brown before they are absolutely black. In coml\ntion, the blackness which announces the complete ignit\nis preceded always by the same mellow, orange col<\nThe representation of this process was probably inten<\nby the Greeks in the black and subdued orange of tl\nvases : indeed, the very colours may have been first p\nduced in the kiln. But without supposing that they w\nretained merely from this accident, the fact that the com\nnation itself is extremely harmonious, would be sufBci\nto account for its adoption. Many of the remarks\nAristotle* and Theophrastusf on the production of blai\nare derived from the observation of the action of fire, a\non one occasion, the former distinctly alludes to the ter\ncotta kiln. That the above opinion as to the nature\nblack was prevalent in the sixteenth century, may be\n\n* \" Do ColoribuB.\" t \" De Igne.\"\n\nferred from Lomazzo, who observes, — \" Quanto all' origine\ne gencrazione de' colori, la frigidity e la madre della bian-\nchezza : il calore e padre del nero.\"* The positive cold-\nness of black maj be said to begin when it approaches\ngre;. When Leonardo da Vinci says that black is mott\nbeautiful in shade, he probably means to define its most\nintense and transparent state, when it is furthest removed\nfrom grey.\n\nNOTE v.— Par. 555.\n\nTbe nature of vehicles or liquid mediums to combine\nwith the substance of colours, has been frequently discussed\nby modern writers on art, and may perhaps be said to have\nreceived as much attention as it desenes. Reynolds smiles\nat the notion of our not having materials equal to thdsc of\nformer times, and Indeed, although the methods of indivi-\nduals will always differ, there seems no reason to suppose\nthat any great technical secret has been lost In these in-\nquiries, however, which relate merely to the mechanical\ncauses of bright and durable colouring, the skill of tbe\npainter in the adequate employment of tbe higher resources\nof his art is, as if by common consent, left out of the account,\nand without departing from this mode of considering the\nquestion, we would merely repeat a conviction before ex-\npressed, viz. that the preservation of internal brightness, a\nquality compatible with various methods, has had more to\ndo with the splendour and durability of finely coloured pic-\ntures than any vehicle. The observations that follow are\ntherefore merely intended to show how far the older written\nauthorities on this subject agree with the results of modern\ninvestigation, without a! all assuming that the old methods,\nif known, need be implicitly followed.\n\nOn a careful examination of the earlier pictures, it is said\n\nit mult be admined.\n\n400 NOTES.\n\nthat a resinous substance appears to have been mingled with\nthe colours together with the oil ; that the fracture of the\nindurated pigment is shining, and that the surface resists the\nordinary solvents.* This admixture of resinous solutions or\nvarnishes with the solid colours is not alluded to, as far as\nwe have seen, by any of the writers on Italian practice, but\nas the method corresponds with that now prevalent in\nEngland, the above hypothesis is not likely to be objected to\nfor the present.\n\nVarious local circumstances and relations might seem to\nwarrant the supposition that the Venetian painters used\nresinous substances. An important branch of commerce\nbetween the mountains of Friuli and Venice still consists in\nthe turpentine or fir-resin. | Similar substances produced\nfrom various trees, and known under the common name of\nbalsams,;]; were imported from the East through Venice, for\ngeneral use, before the American balsams§ in some degree\nsuperseded them ; and a Venetian painter, Marco Boschini,\nin his description of the Archipelago, does not omit to speak\nof the abundance of mastic produced in the island of Scio.jj\n\nThe testimonies, direct or indirect, against the employ-\n\n* See \" Marcucci Sag^o Analitico-chimico sopra i colori,\" &c. Rome, 1816,\nand '* Taylor's Translation of Merim^e on Oil-painting,\" London, 1839. The\nlast-named work contains much useful information.\n\nf Italian writers of the 16th century speak of three kinds. Cardanus says,\nthat of the (tbiei was esteemed most, that of the larix next, and that of the\npicea least. The resin extracted by incision from the last (the pinus abies\nLinnasi) is known by the name of Burgundy pitch ; when extracted by fire it\nis black. The three varieties occur in Italian treatises on art, under the\nnames of oglio di abexxo, trementina and pece Greca,\n\nI The concrete balsam benzoe, called by the Italians beiuzino, and be/-\nzoino, is sometimes spoken of as a varnish.\n\n( Marcucci supposes that balsam of copaiba was mixed with the pigments\nby the (later) Venetians.\n\nII \" L' Archipelago con tutte le Isole,\" Ven. 1658. The incidental notices\nof the remains of antiquity in this work would be curious and important if\nthey could be relied on. In describing the island of Samos, for instance, the\nauthor asserts that the temple of Juno was in tolerable preservation, and that\nthe statue was still there.\n\nment of any such aubitances by the Venetian pwnten, in the\nsolid part of their work, seem, notwithstanding, very con-\nclusive ; we begin with the writer just named. In his prin-\ncipal composition, a poem * describing the practice and the\nproductions of the Venetian painters, Boscbini speaks of\ncertain colours which they shunned, and adds : — \" In like\nmanner (they avoided) shining liquids and varnishes, which\nI should rather call lackers ;f for the surface of flesh, if\nnatural and imadomcd, assuredly does not shine, nature\nspeaks as to this plainly.\" After alluding to the possible\nalteration of this natural appearance by means of cosmetics,\nhe continues : \" Foreign artists set such great store by these\nvarnishes, that a shining surface seems to them the only de-\nsirable quality in art. What trash it is ihey prize ! fir-resin,\nmastic, and sandarach, and larch-resin (not to say treacle),\nstuff (it to polish boots.]; If those great painters of ours\nhad to represent armour, a gold vase, a mirror, or anything\nof the kind, they made it shine with (simple) colours.\"§\n\nThis writer so frequently alludes to the Flemish painters,\nof whose great reputation he sometimes seems jealous, that\nthe above strong expression of opinion may have been\npointed at them. On the other hand it is to be observed\nthat the term forestieri, strangers, does not necessarily mean\ntransalpine foreigners, but includes those Italians who were\n\n■ '• Ls Cuta del Navegai HtoieKo,\" Ven. 1660. It U in the Vanetiaa\ndialect.\n\nt Inrgriadure (inretiiatuie), literellj the g\\asng applied to eaxtliBawaie.\nt \"O de che itiuiB k (an c»edal 1\n\nRobe, che ilkulrerave ogni itisal.\" — p. 338,\nThe allitsratioD of tha worda trcmtiilina mnd Iriaca i> of coun« loit ia &\niruuUtion.\n\n4 \" I li ha fati Btialuier co' i colori.\" BoKhini wu at leiut cotutuit in his\nopintun. In the >eciiiid edition of his \" Ricche Miiiere dells Pittura Veno-\niacia,'* which appeared fourteen years after iho publication of hia poem, he\nrepents that the Venetiau painlenaioided wiDe colounin fleeh \" e umilmenle\n\n402 NOTES.\n\nnot of the Venetian state.* The directions given bj\nRaphael Borghini.f and after him by Armenini^]]! respect-\ning the use and preparation of varnishes made from the very\nmaterials in question, may thus have been comprehended in\nthe censure, especially as some of these recipes were €X>pied\nand republished in Venice by BisagnOj§ in 1642 — that is,\nonly six years before Boschini*s poem appeared.\n\nRidolfi*s Lives of the Venetian Paintera|| (1648) may be\nmentioned with the two last. His only observation respect-\ning the vehicle is, that Giovanni Bellini, after introducing\nhimself by an artifice into the painting-room of Antonello\nda Messina, saw that painter dip his brush from time to\ntime in linseed oil. This story, related about two hun-\ndred years after the supposed event, is certainly not to be\nadduced as very striking evidence in any way.^\n\nAmong the next writers, in order of time prior to Bisagno,\nmay be mentioned Canepario** (l6l9). His work^ \" De\nAtramentis*' contains a variety of recipes for different pur-\nposes : one chapter, De atramentis diversicdoribuit, has a\nmore direct reference to painting. His observations under\nthis head are by no means confined to the preparation of\ntransparent colours, but he says little on the subject of\n\n* Thus, in the introduction to the ** Ricche Minere,\" Boschini calls the\nMilanese, Florentine, Lombard, and Bolognese painters, /bre«/>rri.\n\nt \"II Ripow,\" Firenxe, 1584.\n\n♦ \" De» Veri Precetti della Pittura,\" Ravenna, 1587.\n\n§ \" Trattato della Pittura fondato nell* autoriUl di molti eccellenti in qnesta\nprofeiwione.\" Venexia, 1642. Bisagiio remarks in his preface, that the books\non art were few, and that painters were in the habit of keeping them secret.\nHe acknowledges that he has availed himself of the labours of others, but\nwithout mentioning his sources : some passages are copied from Lomano.\nHe, however, lays claim to some original observations, and says he had seen\nmuch and discoursed with many excellent painters.\n\nII « Le Meraviglie delP Arte,'' Venezia, 1648.\n\n% It has been conjectured by some that this story proved the immixture of\nvaniishos with the colours, and that the oil was only used to dilute them.\nThe epitaph on Antonello da Messina which existed in Vasari's time, alludes\nto his having mixed the colours with oil.\n\n** ** Petri Maris Caneparii De Atramentis cujuscumque generis,\" Venet.\n1619. It was republished at Rotterdam in 1718.\n\nNOTES. 403\n\nvamishes. After describing ft mode of preserving white of\negg, he says, \"Others are accustomed to mix colours in\nliquid varnish and linseed, or nut-oil ; for a liquid and oily\nvarnish binds the (diSerent layers of) colours better U^e-\nther, and thus forms a very fit glazing material.\"* On the\nsubject of oUs he observes, that linseed oU was in great re-\nquest among painters ; who, however, were of opinion that\nnut-oil excelled it \" in giving brilliancy to pictures, in pre-\nserving them better, and in rendering the colours more\nrivid.\"-!-\n\nLomazzo (a Milanese) says nothing on the subject of\nvehicles in his principal work, hut in his \" Idea del Tempio\ndella Pittura,\"^ he speaks of grinding the colours \" in nut-\noil, and spike-oil, and other things,\" the \" and\" here evidently\nmeans or, and by \" other things\" we are perhaps to under-\nstand other oils, poppy oil, drying oils, &c.\n\nThe directions of Raphael Borgbini and Vasari § cannot\ncertainly he conudered conclusive as to the practice of the\nVenetians, hut they are very clear on the subject of varnish.\nThese writers may he considered the earliest Italian autho-\nrities who have entered much into practical methods. In\nthe few observations on the subject of vehicles in Leonardo\nda Vinci's treatise, \" there is nothing,\" as M. Merim^e ob-\nserves, \" to show that he was in the habit of mixing varnish\nwith his colours.'' Cenmni says but little on the subject\n\n* \" lis quod magia ex hiu evxUl atntnenttUD pietune niminDpeTe idoneum.\"\nTbiu, italrawHntiim ii to be imdentood.uaaual, tomean a glaiiiig colour, the\npawage can only refei to tlie inuoixtiira of vamiih with the ttatupartait colour*\n^iplied lait in order.\n\nf In a pBHa^ tbat followa recpeeting the mode of eitracling nut-oil,\nCanepariui appean to minlranslate OaJeti, c. 7 — \" De Simplicium Medica-\ntoeiitorum facultatibus.\" The obiervalionii of Qalen on thit gubjecl, and on\nthe drying property of linseed, may have given the flrst hint to the inrenlort of\noil-painting. The cuitoni of doting the origin of thii art from Van Eyck it\nlike that of dating the eamTneneemeDt of modem painting from Cimabue.\nThe improver i> often ammied to be the iDTentc*.\n\nI Milan, 1591).\n\nf Tbe particular! here alluded lo are to be found in (he Bnt editjon of\nVa»ii (13S0) ai veil aa the second.— v. i. c. 21, &i.\n\n2 d2\n\n404 NOTES.\n\nof oil-painting ; Leon Battista Alberti is theoretical rati\nthan practical, and the published extracts of Lorenzo Gl\nberti's MS. chiefly relate to sculpture.\n\nBorghini and Vasari agree in recommending' nut-oil\npreference to linseed-oil ; both recommend adding* vami\nto the colours in painting on walls in oil^ \" because ti\nwork does not then require to be varnished afterwards\nbut in the ordinary modes of painting on panel or clot\nthe varnish is omitted. Borghini expressly says^ that c\nalone (senza piu) is to be employed ; he also recommend\na very sparing use of it\n\nThe treatise of Armenini (1587) was published ;\nRavenna^ and he himself was of Faenza, so that his autfa<\nrity^ again, cannot be considered decisive as to the Venetia\npractice. After all, he recommends the addition of *' con\nmon varnish** only for the ground or preparation, as a coc\nsolidating medium, for the glazing colours, and for thos\ndark pigments which are slow in drying. Many of hi\ndirections are copied from the writers last named ; the re\ncipes for varnishes, in particular, are to be found in Bor\nghini. Christoforo Sorte* (1580) briefly alludes to th\nsubject in question. After speaking of the methods of dis\ntemper, he observes that the same colours may be used ii\noil, except that instead of mixing them with size, they ar<\niqixed on the palette with nut-oil, or (if slow in drying) witl\nboiled linseed-oil : he does not mention varnish. Th<\nItalian writers next in order are earlier than Vasari, anf\nmay therefore be considered original, but they are all ver^\nconcise.\n\n* ** Osserrazioni nella Pittura.'* In Venezia, 1580. Sorte, who, it appean\nwas a native of Verona, had worked in his youth with Oiulio Romano, a\nMantua, and communicates the methods taught him by that painter, for givinj\nthe true effects of perspective in compositions of figures. He is, perhaps, thi\nearliest who describes the process of water-colour painting as distinguiahec\nfrom distemper and as adapted to landscape, if the art he describes deseirei\nthe name.\n\nNOTES: 405\n\nThe treatise of Michael Angelo Biondo* (1549), re-\nmarkable for its historical mistakes, is not without interest\nin other respects. The list of colours he gives is, in all\nprobahility, a catalt^ue of those in general use in Venice at\nthe period he wrote. With regard to the vehicle, he merely\nmentions oil and size as the mediums for the two distinct\nmethods of oil-painting and distemper, and docs not speak\nof varnish. The passages in the Dialogue of I>oni-( (1549),\nwhich relate to the subject in question, are to the same\neffect. \" In colouring in oil,\" he observes, \" the most\nbrilliant colours (that we see in pictures) are prepared by\nmerely mixing them with the end of a knife on the palette.\"\nSpeaking of the perishable nature of works in oil-painting\nas compared with sculpture, he says, that the plaster of\nParis (gesso) and mastic, with other ingredients of which\nthe ground is prepared, are liable to decay, &c. ; and else-\nwhere, in comparing painting in general with mosaic, that\nin the former the colours \" must of necessity be mixed with\nvarious things, such as oils, gums, white or yolk of egg, and\njuice of figs, ail which tend to impair the beauty of the tints.\"\nThis catalf^ue of vehicles is derived from all kinds of paint-\ning to enforce the argument, and is by no means to be\nunderstood as belonging to one and the same method.\n\nAn interesting little work,| still in the form of a dialogue\n(Fabio and Lauro), appeared a year earlier ; the author,\nPaolo Pino, was a Venetian painter. In speaking of the\npractical methods Fabio observes, as usual, that oil-painting\nis of all modes of imitation the most perfect, but his reasons\nfor this opinion seem to have a reference to the Venetian\n\n■ \"Delia Dobiliuima Httura e nu Arte,\" Veneua, 1549. Biondn i« ao\nignoruil u to attribute the Laat Supper, by Lecnudo da Vioci, to MaDtegna.\n\nt \" Dia^no del Doni,\" in Veoezi*, 1&49.\n\ni \"Dialogo di Pitti^fB,\" Veuena, 1548. Htio, in enumerating the cele-\nbrated eonlemporary ititUt, doea not inclode Paul Verooeie, for a very\nobvious teaton, that paintec being at the time only about 17 years of a^e.\nSorte, who wrote thirty yean later, mentions \"I'eciwliente Messer Paulinu\n\n40ft NOTES.\n\npractice of going over the work repeatedly. Laoro aak\nwhether it is not possible to paint in oil on the dry wall, ai\nSebastian del Piombo did. Fabio answers, ''the worl\ncannot last, for the solidity of the plaster is impenetrable\nand the colours, whether in oil or distemper, cannot pasi\nthe surface/' This might seem to warrant the inference\nthat absorbent grounds were prepared for oil-painting, but\nthere are proofs enough that resins as well as oil were used\nwith the gesso to make the preparation compact. See Doni,\nArmenini, &c. This writer, again, does not speak of var-\nnish. These appear to be the chief Venetian and Italian\nauthorities* of the sixteenth and part of the following cen-\ntury ; and although Boschini wrote latest, he appears to have\nhad his information from good sources, and more than once\ndistinctly quotes Palma Giovane.\n\nIn all these instances it will be seen that there is no allu-\nsion to the immixture of varnishes with the solid colours,\nexcept in painting on walls in oil, and that the processes oi\ndistemper and oil are always considered as separate arts.*f\n\n* The IMalogues of Lodovico Dolce, and various other works, are not re-\nferred to here, as they contain nothing on the tnibject in question. The latest\nauthority at all connected with the traditions of Venetian practice, is a certain\nGiambatiiita Volpato, of Uassaiio : he died in 1706, and had been intimate\nwith Ridolfi. The only circumstance he has transmitted relating to practical\ndetails is that Giacomo Bassan, in retouching on a dry surface, sometimei\nafiopted a method commonly practised, he says, by Paul Veronese (and com-\nmonly practised still), namely, that of dippii^ his brush in spirits of turpen-\ntine ; at other times he oiled out the surface in the usual manner. Volpatc\nleft a MS. which was announced for publication in Vicenxa in 1685, but if\nne\\'er appeared ; it, however, afterwards formed the ground-work of Verci'a\n\" Notixie intomo alia Vita e alle Opere de' Pittori di Bassano.\" Veuexia,\n1775. See also \" Lettera di Giambatista Rol>erti sopra Giacomo da Ponte,*'\nLugano, 1777. Another MS. by Natale Melchiori, of about the same date, is\npreserved at Treviso and Castel Franco : it alxmuds with historical mistakes ;\nthe author says, for instance, that the Pietro Martyre was begun by Oior-\ngione and finished by Titian. The recipes for varnishes and colours are very\nnumerous, but they are mostly copied iirom earlier works.\n\nt That distemper was not very highly c8teome<l by the Venetians may be\ninferred from the following observation of Pino : — ** 11 modo di colorir 1^\nguazzo d imperfetto et piil fragile et k me non diletta onde lasciamolo all*\n\nNOTES. 407\n\nOn the other hand, the pruhibition of Boachini cftiinot be\nunderstood to be universal, for it is quite certain that the\nVenetians varnished their pictures when done.* After\nTitian had finished his whole-length portrait of Pope Paol\nIII. it was placed in the sun to he varnished.t Again, in\nthe archives of the church of S. Niccolo at Treviso a sum\nis noted (Sept. 21, 1521), \"per far la vemise da invemisar\nla Pala dell' altar grando,\" and the same day a second entry\nappears of a payment to a punter, \" per esser venuto a dar\nla vemise alia Pala,\" &c.| It is to be obsen-ed that in\nboth these cases the pictures were varnished as soon as\ndone ;§ the varnish employed was perhaps the thin com-\npound of naphtha (o^lio di sasso) and melted turpentine\n(oglio d'abezzo), described by Borghini, and after bim by\nArmenini : the last-named writer remarks that he had seen\n\noltrnnoDtaiii i qiuli «>n(i priri dells veia rift.\" It u, bowsrei, certain that\nthe Venetian! wmetiiDca paiated in tbii itf le, and Volpato menlioiu MTeial\nwork* of the kind bj Banan, but he never binti that he began bit oil picturea\nin diitempcT.\n\n* Bwcluiii eayt, that the VenetiuB (ha eipeciall]' meaiu Utian) rendered\ntheir pictiuei ipukling bjr finally touching on a dry rarfaca (d ncco). The\nabaence of vaiuiah in tha aolid coloun, the ralouchin); with apirit of tuipen-\nline, and even a ticeo, all luppoee a dull surface, which would require Tar>\nninh. The latter method, alluded to by Bowhini, wai an eieeptiou to the\ngeneral practice, and tiot likely to be followed on account of it> difficulty.\nCarlo MaraCd, on the aulhoiily of Palomino, uied to lay, \" He must be a\n■kilfiil painter who can retouch without ailing out.\"\n\nt Bee a letter by Frattceico Boechi, and another by Vauri, in tha \" Lettere\nPittoriche\" of Bottari. The ciicunutaui'e ii mentioned inci dentally ; the\npoint chiefly dwelt on ia, that lome peratma who paiaed were deceired, and\nbowed to the pivture, (uppueing it to be the pope.\n\n\\ Federici, \" Memorie Ttevigiane,\" Veneaa, 1803. The altar-piece of\n8. Niceolo at Treriao is attributed, in the document alluded to, to Pra Marco\nPeniabene, a name unknown ; the painting is eo eicellent ai tD have been\ntheagbt worthy of Bebaatian del nombo : for tbi* opinion, however, there are no\nhialorical grouud*. It waa begun in 1520, bu) before it wai quite flniehed the\n]>ainter, whoever he waa, abaconded : it wai therefore completed by another.\n\nf Titian'a atay in Rome wai ■boit, and with reaped to the Tieviao altar-\n(Ueee, a week or two only, at moat, can have elapaed between the eoinpletion\nand the vamiahing. Cenniiii, who recummenda delaying a year at leaat be-\nfore vatniahing, apeaka of picturea in diatemper.\n\n408 NOTES.\n\nthis varnish used by the best painters in Lombardy, and\nhad heard that it was preferred by Correggio. The conse-\nquence of this immediate varnishing may have been that the\nwarm resinous liquid^ whatever it was, became united ¥rith\nthe colours, and thus at a future time the pigment may have\nacquired a consistency capable of resisting the ordinary sol-\nvents. Not only was the surface of the picture required to\nbe warm, but the varnish was applied soon after it was taken\nfrom the fire.*\n\nMany of the treatises above quoted contain directions for\nmaking the colours dry :f some of these recipes, and many\nin addition, are to be found in Palomino, who, however de-\nfective as an historian.;]; has left very copious practical\ndetails, evidently of ancient date. His drying recipes are\nnumerous, and although sugar of lead does not appear, car-\ndenillo (verdigris), which is perhaps as objectionable, is\nadmitted to be the best of all dryers. It may excite some\nsurprise that the Spanish painters should have bestowed so\nmuch attention on this subject in a climate like theirs, but\nthe rapidity of their execution must have often reoulred\nsuch an* assistance. §\n\nOne circumstance alluded to by Palomino, in his very\nminute practical directions, deserves to be mentioned. After\n\n* See Borghiiii, Armenini, their Venetian copyist Bisagno, and Palomino.\nThe last-named writer, though of another school and much more modem, was\nevidently well acquainted with the ancient methods: hesays, **Se advierte\nque siempre que se huviere de bamizar alguna cosa conviene que la pintura y\nel baniiz esten calicntes.\" — El Muieo Pictorico, v. ii.\n\nt Burnt alum, one of the ingredients recommended, might perhaps account\nfor a shining fracture in the indurated pigment in some old pictures.\n\nX Of the earlier Spanish writers Paeheco ivay be mentioned next to Palo-\nmino as containing most practical information. Carducho, De Butron, and\nothers, sehlom descend to such details. Palomino contains all the directions\nof Paeheco, and many in addition.\n\n( See Cean Bermudei, \"* Sobre la Escuela Sevillana,'' Cadii, 1806. The\nsame reasons induced the later Venetian machinists to paint on dark grounds,\nand to make use of (drying) oil in excess. See Zanetti, Delia Pittura Fent^\n*inma, 1. iv.\n\nNOTES. 409\n\n•ajing what colours aboult] be preserved in their sancera\nunder water, and what coloun should be merely covered\nwilh oiled paper because the water injures them, he pro-\nceeds to cooimunicate \"a curious mode of preserving oil-\ncolours,\" and of transporting them from place to place.\nThe important secret is to tie them in bladders, the mode\nof doing which be enters into with great minuteness, as if\nthe invention was recent, tt Is true, Christoforo Sorte, in\ndescribing bis practice in water-colour drawing, says he was\nin the habit of preserving a certain v^etable green with\ngum-water in a bladder ; but as the method was obviouslj\nnew to Palomino, there seems sufficient reason to believe\nthat uil-colours, when once ground, had, up to his time, been\nkept in saucers and presen-ed under water.* Among the\nitems of expense in the Trcviso document before alluded\nto, we find \"a pan and saucers for the painters,\"! This 19\nin accordance with Cennini's directions, and the same »ya-\ntem appears to have been followed till after 1700.^\n\nThe Flemish accounts of ihe early practice of oil-painting\nare all later than Vasari. Van Maader, in correcting the\nItalian historian in his dates, still follows his narrative in\nother respects verbatim. !f Vasari's story is to be accepted\nas true, it might be inferred that the Flemish secret con-\nsisted in an oil varnish like copal.§ Vasari says, that Van\n\n* Barghini, in tleicribiiig the melbod at making a gotd-tiie (the *ame >■\nCenuini's), spealu of bailing the \" buccie de* cotari\" in oil ; this ouly meana\nthe akin or pellicle of (lie colour itself — in fact, he proceeds to uy tliat they\ndinolve in boilii^. Va«ui, in deKiibing the lame proeeu, (uea the eiptea-\n■ioii \" coiaii seccttticci.\"\n\nt \" MagKio 4 (1520) Per no cadin (catino) par depantori. Per KudeUini\nperli depentori.\" — Mem. Trev., vol. i. p. 131. Pungileoni (\" Memorio l»to-\nricbedi Antonio Alli^i\") qnotei a noteofeipensci relating to two oil-pictUTM\nby Paolo Oianotti -, among the itema «e find \"colori, telaii, el ttrocchette.\" —\n\n1 Salman, in hit \"Folygraphice'' (1701), givei the fallowing direction :—\n\" Oyl colora, if not preienlly used, will have * ikin grow over them, to pre-\nvent which put them into a glara, Bnd put the glau three or four iochei under\n\ni This TBTiiiih appeal) to have been known aoma centuriei before Van\nEjrek'a lime, but he may have been the fint to mil it wilh the coloun.\n\n410 NOTES.\n\nEyck boiled the oils with other ingredients ; that the colours^\nwhen mixed with this kind of oil, had a rerj firm con-\nsistence ; that the surface of the pictures so executed had a\nlustre, so that thej needed no varnish when done ; and that\nthe colours were in no danger from water.*\n\nCertain colours, as is well known, if mixed with oil alone,\nmay be washed off after a considerable time. Leonardo\nda Vinci remarks, that verdigris may be thus removed.\nCarmine, Palomino observes, may be washed off after six\nyears. It is on this account the Italian writers recommend\nthe use of varnish with certain colours, and it appears the\nVenetians, and perhaps the Italians generally, employed it\nsolely in such cases. But it is somewhat extraordinary that\nVasari should teach a mode of painting in oil so different\nin its results (inasmuch as the work thus required varnish\nat last) from the Flemish method which he so much ex-\ntols — a method which he says the Italians long endeavoured\nto find out in vain. If they knew it, it is evident, assuming\nhis account to be correct, that they did not practice it.\n\nNOTE W.— Par. 608.\n\nIn the second volume Goethe gives the nomenclature of\nthe Greeks and Romans at some length. The general no-\ntions of the ancients with regard to colours are thus de-\nscribed : — *' The ancients derive all colours from white and\nblack, from light and darkness. They say, all colours are\nbetween white and black, and are mixed out of these. We\nmust not, however, suppose that they understand by this a\nmere atomic mixture, although they occasionally use the\nword /x/$iy;f for in the remarkable passages, where they\nwish to express a kind of reciprocal (dynamic) action of the\ntwo contrasting principles, they employ the words npaais,\nunion, avyKpiaiSt combination ; thus, again, the mutual in-\nfluence of light and darkness, and of colours among each\n\n* See Vasari, Life of Antunello da Messina,\nt See Note on Par. 177.\n\nNOTES. 411\n\nOther, U described by the word xtpdnuabah ao apreuion of\n■unilar import.\n\n\"The varieties of colours are di&ereatly enumerated;\naojae mention seven, others twelve, but without giving the\ncomplete list. From a consideration of the terminology\nboth of the Greeks and Romans, it appears that they some-\ntimes employed general for specific terms, and nice wfrsa.\n\n\" Their denominations of colours are not permanently and\nprecisely defined, but mutable and fluctuating, for they are\nemployed even with r^;ard to similar colours both on the\npliu and mmuf side. Their yellow, on the one hand, in-\nclines to red, on the other to blue; the blue is sometimes\ngreen, sometimes red; the red is at one time yellow, at\nanother blue. Pure red (purpur) fluctuates between warm\nred and blue, sometimes inclining to scarlet, sometimes to\nviolet.\n\n\"Thus the ancients not only seem to have looked upon\ncolour as a mutable and fleeting quality, but appear to have\nbad a presentiment of the (physical and chemical) effects\nof augmentation and re-action, In speaking of colours\nthey make use of expressions which indicate this knowledge;\nthey make yellow redden, because its augmentation tends\nto red ; they make red become yellow, for it often returns\nthus to its origin.\n\n\" The hues thus specified undergo new modifications.\nThe colours arrested at a given point are attenuated by a\nstronger light darkened by a shadow, nay, deepened and\ncondensetl in themselves. For the gradations which thus\narise the name of the species only is often given, but the\nmore generic terms are also employed. Every colour, of\nwhatever kind, can, according to the same view, be multi-\nplied into itself, condensed, enriched, and will in conse-\nquence appear more or less dark. The ancients called\ncolour in this state,\" Sec. Then follow the designations of\ngeneral slates of colour and those of specific hues.\n\nAnother essay on the notions of the ancients respecting\n\n412 NOTES,\n\nthe origin and nature of colour generally, shows how nearly\nGK>ethe himself has followed in the same track. The\ndilating effect of light objects, the action and reaction of the\nretina, the coloured after-image, the general law of contrast,\nthe effect of semi-transparent mediums in producing warm\nor cold colours as they are interposed before a dark or light\nbackground — all this is either distinctly expressed or hinted\nat ; \" but,\" continues Goethe, '* how a single element\ndivides itself into two, remained a secret for them. They\nknew the nature of the magnet, in amber, only as attraction ;\npolarity was not yet distinctly evident to them. And in\nvery modern times have we not found that scientific men\nhave still given their almost exclusive attention to attraction,\nand considered the immediately excited repulsion only as a\nmere after-action?\"\n\nAn essay on the Painting of the Ancients* was contributed\nby Heinrich Meyer.\n\nNOTE X.— Par. 670.\n\nThis agrees with the general recommendation so often\ngiven by high authorities in art, to avoid a tinted look in the\ncolour of flesh. The great example of Rubens, whose\npractice was sometimes an exception to this, may however\nshow that no rule of art is to be blindly or exclusively\nadhered to. Reynolds, nevertheless, in the midst of his\nadmiration for this great painter, considered the example\ndangerous, and more than once expresses himself to this\neffect, observing on one occasion that Rubens, like Baroccio,\nis sometimes open to the criticism made on an ancient\npainter, namely, that his figures looked as if they fed on\nroses.\n\nLodovico Dolce, who is supposed to have given the viva\nvoce precepts of Titian in his Dialogue,! makes Aretino\n\n♦ Vol. ii. p. 69, first edition.\n\nt ** Dialog della Pittura, intitolato PAretino.'' It was first published at\nVenice in 1557 ; about twenty years before Titian's death. In the dedication\n\nNOTES. 413\n\nsay : \" I would generally baniab from my pictures those\nvermilion cheeks with coral Iip> ; for faces thus treated look\nlike masks. Propertius, reproving his Cynthia for unng\ncosmetics, desires that her complexion might exhibit the\nsimplicity and purity of colour which is seen in the works of\nApelles,\"\n\nThose who have written on the practi<» of painting have\nalways recommended the use of few colours for flesh.\nReynolds and others quote even ancient authorities as re-\ncorded by Pliny, and Boschini gives several descriptions of\nthe method of the Venetians, and particularly of Titian, to\nthe same effect. \" They used,\" he says, \" earths more than\nany other colour, and at the utmost only added a little ver-\nmilion, minium, and lake, abhorring as a peBtilence hiadetti,\ngialli santi, nnaltini, verdi-azxurri, giaUolini,\"* Else-\nwhere he says.f \" Earths should be used rather than other\ncolours :\" after repealing the above prohibited list he adds,\n\" I speak of the imitation of flesh, for in other things every\ncolour is good ;\" again, \"Our great Titian used to say that\nhe who wishes to be a painter should be acquainted with\nthree colours, white, black, and Ted.\";|| Assuming this\n\nto the nenatoi Loreduio, Lodovico Dolce eul(^;iM> the work, which he would\nhardly have done if it hod been entirely hii own : agun, the nippautioii that\nit nuy have been niggeated by Aietino, would be equally iioucluBiTe, coupled\nwith internal evidence, a* to the ariginal aource.\n\n* Introduction to the \"Ricche Miners dellaPittnra Veoenatia,\" Veneua,\n1674. The Italian annotatora on older worlu ou paintiug are Bometimei at a\nIon to And modem temu equivalent to the obeolete nameii of pigments. (^See\n\" Antologia dell 'Arte nttorica.\") The eoloun now in uae correapomling with\nBoachini'i liil, are probably yellow lakaa, nualt, verditet, and Naples yellow.\nBoschini often censures the pracKce of other tchools, and in this eniphD.tic\ncondemnation he seems to hare hod an eye to certain precepts in Lomaao,\nand perhaps, even in Leonardo da Vinei, who, on one occasion, recommends\nNaples yellow, lake, and white for flesh. The Venetian writer often speaks,\ntoo, in no measured terms of certain Flemish pictures, pruliably because thef\nappeared to him Coo tinted.\n\nt \"La Carta tiel Navegar Pitoresco,\" p. 33M.\n\nt lb. p. 341. In describing Titian's actual practice (\" Bicehe Minete\"J,\nhe, howerer, odds yellow (ochre). The red it also parficularis*i, lU., the\n\n414 NOTES.\n\naooount to be a little exaggerated, it is still to be observed\ntliat the monotony to which the use of few colours would\nseem to tend, is prevented by the nature of the Venetian\npiocess, which was sufficiently conformable to Goethe*s\ndoctrine ; the gradations being multiplied, and the effect of\nthe colours heightened by using them as semi-opaque me-\ndiums. Inunediately after the passage last quoted we read,\n\"He also gave this true precept, that to produce a lively\ncolouring in flesh it is not possible to finish at once.\"* As\nthese particulars may not be known to all, we add some\nfurther abridged extracts explaining the order and methods\nof these different operations.\n\n\" The Venetian painters,*' says this writer, | \" after\nhaving drawn in their subject, got in the masses with very\ntaiid colour, without making use of nature or statues. Their\ngreat object in this stage of their work was to distinguish\nthe advancing and retiring portions, that the figures might\nbe relieved by means of chiaro-scuro— one of the most im-\nportant departments of colour and form, and indeed of in-\nvention. Having decided on their scheme of efiEsct, when\nthis preparation was dry, they consulted nature and the\nantique ; not servilely, but with the aid of a few lines on\npaper (jquatirn segni in carta) they corrected their figures\nwithout any other model. Then returning to their brushes,\nthey began to paint smartly on this preparation, producing\nthe colour of flesh.\" The passage before quoted follows,\nstating that they used earths chiefly, that they carefully\navoided certain colours, '' and likewise varnishes and what-\never produces a shining surface. J When this second painting\nwas dry, they proceeded to scumble over this or that figure\nwith a low tint to make the one next it come forward, giving\nanother, at the same time, an additional light — for example,\n\n* High examples here again prove that the opposite syttem may attain\nresults quite as successful.\n\nf Introduction to the \" Ricche Minere.\"\n\nX See Note to Par. 555. Here again, assuming the description to be cor-\nrect, high authorities might be opposed to the Venetians.\n\nNOTES. 415\n\n&a a bead, a hand, or a foot, thus detaching them, so to ^)ed£,\nfrom the canvM.\" (Tintoret's Prigioma di S. Rocco is here\nquoted.) \" B^ thus alill multiplying these well -understood\nTetoucbings where required, on the dry surface, (a secco)\nthey reduced the whole to harmony. In this opernticm tbey\ntook care not to cover entire figures, but rather went oa\ngemming them (gtoielandoU) with vigorous touches. Id\nthe shadows, loo, tbey infused vigour frequeotly by glazing\nwith asphftltum, always leaving great masses in middle-tint,\nwith many darks, in addition to the partial glazings, and\nfew lights.\"\n\nThe introduction to the subject of Venetian colouring, in\nthe poem by the same author, is also worth transcribing, hut\nas the style is quaint and very concise, a translation is neces-\nsarily a paraphrase.*\n\n\" The art of colouring has the imitation of qualities for\nits object ; not all qualities, but those secondary ones which\nare appreciable by the sense of sight The eye espedsUy\nsees colours, the imitation of nature in painting is therefore\njustly called colouring; but the painter arrives at his end\nby indirect means. He gives the varieties of tone in masses ;f\n\n* The followuig quatrun ma^ aerre ai a ipecimcD ; the author u speaking\nof thi impDTtuue of thaeolfnii of fieah as conduciTa to pictuieaquB effect: —\n\" Importa el node ; e come ben I'lmporta !\nXIn quadro warn nudo i come aponto\nVn dimar unn pan, *e ben ghe anito.\nPer pill delicia, confetuia e torta.\" — p. 346.\nIn his preface he aulicipatea, and tbiu anaren the objectiiHis to bit Venetian\n^aled — \" Mi, che son Tenetian in Venetia e cha park de' Pilori Venetiani\nhi da andarme a atiaveetirl Ouarda el Cielo.\"\n\nt The void Macchia, lileiolly a blot, ii generally used by tlaliaa writer*,\nby Vasari for instance, for tbe local colour. Doschini underalanda by it the\nrelatire depth of (ones ratber than the mere difference of hue. \" B]-maccbia,\"\nhe saya, \" 1 understand that treatment by which the Qgurea are diatin^iahed\nfrom each other by different tones lighter or darker.\" — La Carlo del\nfiavegar, p. 328. Elsewhere, \" Colouring (as practised by the Venetians)\ncompreheDda both the macchia and drawing ;\" (p. 300) thai is, comprehenda\nthe gradation* of light and dark in objects, and tbe parts of objects, and con-\nMqaently, their eeaentjal form. \" Tbe macchia,\" he sddi, '* is the effect of\npractice, and is dictated by the knowledge of what is tequiaite for effect.\"\n\n416 NOTES.\n\nhe smartly impinges lights^ he clothes his preparation with\nmore delicate local hues^ he miites^ he glazes : thus every-\nthing depends on the method, on the process. For if we\nlook at colour abstractedly, the most positive may be called\nthe most beautiful, but if we keep the end of imitation in\nview, this shallow conclusion falls to the ground. The\nrefined Venetian manner is very different from mere direct,\nsedulous imitation. Every one who has a good eye may\narrive at such results, but to attain the manner of Paolo,\nof Bassan, of Palma, Tintoret, or Titian, is a very different\nundertaking.\"*\n\nThe effects of semi-transparent mediums in some natural\nproductions seem alluded to in the following passage —\n** Nature sometimes accidentally imitates figures in stones\nand other substances, and although they are necessarily in-\ncomplete in form, yet the principle of effect (depth) re-\nsembles the Venetian practice.'* In a passage that follows\nthere appears to be an allusion to the production of the\natmospheric colours by semi-transparent mediums, f\n\nNOTE Y.— Par. 672.\n\nThe author's conclusion here is unsatisfactory, for the\ncolour of the black races may be considered at least quite\nas negative as that of Europeans. It would be safer to say\nthat the white skin is more beautiful than the black, because\nit is more capable of indications of life, and indications of\nemotion. A degree of light which would fail to exhibit the\nfiner varieties of form on a dark surface, would be sufficient\nto display them on a light one ; and tlie delicate mantlings\n\n* \" Ma Parivar a la maniera, al trato\n(Verbi gratia) de Paulo, del Bassan,\nDel Vecbio, Tentoreto, e di Tician,\nPer Dio, I'e cosa da deventar mato.'' — ^p. 294, 297.\nf The traces of the Aristotelian theory are quite as apparent in Boschini\nas in the other Italian writers on art ; but as he wrote in the seventeenth\ncentury, his authority in this respect is only important as an indication of th»\nearlier prevalence of the doctrine.\n\nof colour, whether the result of action or emotion, are more\nperceptible for the aame reason.\n\nNOTE Z— Par. 690.\nThe author appears to mean that a degree of brightness\nwhich the organ can bear at all, must of necessity be re-\nmoved from dazzling, white light. The slightest tinge of\ncolour to this brightness, implies that it is seen through a\nmedium, and thus, in painting, the lightest, whitest surface\nshould partake of the quality of depth. Goethe's view here\nagain accords, it must be admitted, with the practice of the\nbest coionrists, and with the precepts of the highest autho-\nrities.— See Note C.\n\nNOTE A A— Par. 732.\nAmple detuls respecting the opinicKis of Louis Bertrand\nCastel, a Jesuit, are given in the historical part. The co-\ninddence of some of his views with those of Goethe is often\napparent : he objects, for instance, to the arbitrary selection\nof the Newtonian spectrum; observing that the fH>lours\nchange with every change of distance between the prism\nand (he recipient surface. — Farbenl. vol. ii. p. 527. Jeremias\nFriedrich Giilich was a dyer in the neighbourhood of\nStulgardt : he published an elaborate work on the technical\ndetails of his own pursuit. — Farberd. vol. ii. p. 630.\n\nNOTE B B— Par. 748.\nGoethe, in bis account of Castel, suppresses the learned\nJesuit's attempt at colorific music (the claveqin oculaire),\nfounded on the Newtonian doctrine. Castel was compli-\nmented, perhaps ironically, on having been the first to re-\nmark that there were but three principal colours. In\nasserting his claim to the discovery, he admits that there is\nnothing new. In fact, the notion of three colours is to be\nfound in Aristotle ; for that philosopher enumerates no\n\n418 NOTES.\n\nmore in speaking of the rainbow,* and Seneca calls them by\ntheir right names. f Compare with Dante^ Parad. c. 33.\nThe relation between colours and sounds is in like manner\nadverted to by Aristotle ; he says — ^' It is possible that\ncolours may stand in relation to each other in the same\nmanner as concords in music, for the colours which are (to\neach other) in proportions corresponding with the musical\nconcords, are those which appear to be the most agreeable.'*;];\nIn the latter part of the l6th century, Arcimboldo, a\nMilanese painter, invented a colorific music ; an account of\nhis principles and method will be found in a treatise on\npainting which appeared about the same time. ** Am-\nmaestrato dal qual ordine Mauro Cremonese dalla viola,\nmusico deir Imperadore Ridolfo II. trov6 sul gravicembalo\ntutte quelle oousonanze che dair Arcimboldo erano segnate\ncoi colori sopra una carta.\"§\n\nNOTE C C— Par. 758.\n\nThe moral associations of colours have always been a\nmore favourite subject with poets than with painters. This\nis to be traced to the materials and means of description as\ndistinguished from those of representation. An image is\nmore distinct for the mind when it is compared with some-\nthing that resembles it. An object is more distinct for the\neye when it is compared with something that diflfers from it.\nAssociation is the auxiliary in the one case, contrast in the\n\n♦ \" De Meteor.,\" lib. 3, c. ii. and iv. He observes that this is the only\neffect of colour which painters cannot imitate.\n\nf \" De Ignib. cosiest.\" The description of the prism by Seneca is another\ninstance of the truth of CastePs admission. The Roman philosopher's words\nare — ** Virgula solet fieri vitrea, stricta vel pluribus angulis in modo clavae\ntortuosss; hec si ex transverse solem accipit colorem talem qualis in arcu\nvideri solet, reddit,\" &c.\n\nX \" De Sensu et sensili.\"\n\n§ \"II Figino, overo del Fine della Pittura,\" Mantova, 1591, p. 249. An\naccount of the absurd invention of the same painter in composing figures of\nflowers and aninials, and even painting portraits in this way, to the great\ndelight of the emperor, will be found in the same work.\n\nNOTES. 419\n\nOther. The poet, of necessity, succeeds best in conveying\nthe impression of external things by the aid of analogous\nrather than of opposite qualities : so far from losing their\nefiect by this means, the images gain in distinctness. Com-\nparisons that are utterly false and groundless never stiike us\nas such if the great end is accomplished of placing the\nthing described more vividly before the imagination. In\nthe common language of laudatory description the colour of\nflesh is like snow mixed with vermilion : these ore the words\nused by Aretiito in one of his letters in speaking of a figure\nof St. John, by Titian. Similar instances withoat end\nmight be quoted from poets : even a contrast can only be\nstrongly conveyed in description by another contrast that\nresembles it.* On the other hand it would be easy to show\nthat whenever poets have attemped the painter's method of\ndirect contrast, the image has failed to be striking, for the\nmind's eye cannot see tbe relation between two colours.\n\nUnder the same category of eSect produced by association\nmay be classed the moral qualities in which poets have\njudiciously taken refuge when describing visible forms and\ncolours, to avoid competition with tbe piunters' elements,\nor rather to att^n their end more completely. But a\nlittle examination would show that very pleasing moral\nassociations may be connected with colours which would\nbe far from agreeable to the eye. All light, positive co-\nlours, light-green, light-purple, white, are pleasing to tbe\nmind's eye, and no degree of dazzling splendour is ofTensive.\nThe moment, however, we have to do with tbe actual sense\nof vision, tbe susceptibility of the eye itself is to be consi-\ndered, the law of comparison is reversed, colours become\nstriking by being opposed to what tbey are not, and their\nmoral associations are not owing to the colours themselves.\n\n\\Ur\n\nlieauly baiig»\n\nupoi\n\n. tlip\n\n.'hrck\n\nDflligh..\n\nLike\n\natk^hjeweli,\n\nlaii\n\nEtl.\n\n,o,.W.\n\n2 E 2\n\n420 NOTES.\n\nbut to the modifications such colours undergo in oonsequenoe\nof what surrounds them. This view, so naturally conse-\nquent on the principles the author has himself arrived at,\nappears to be overlooked in the chapter under oonsidera-\ntion, the remarks in which, in other respects, are acute and\ningenious.\n\nNOTE D D— Par. 849.\n\nAccording to the usual acceptation of the term chiaro-\nscuro in the artist world, it means not only the mutable\neffects produced by light and shade, but also the permanent\ndifferences in brightness and darkness which are owing to\nthe varieties of local colour.\n\nNOTE E E.— Par. 855.\n\nThe mannered treatment of light and shade here alluded\nto by the author is very seldom to be met with in the works\nof the colourists ; the taste may have first arisen from the\nuse of plaster-castS; and was most prevalent in France and\nItaly in the early part of the last century. Piazzetta repre-\nsented it in Venice, Subleyras in Rome. In France\n*' Restout taught his pupils that a globe ought to be repre-\nsented as a polyhedron. Greuze most implicitly adopted\nthe doctrine, and in practice showed that he considered the\nround cheeks of a young girl or an infant as bodies cut into\nfacettes.\"*\n\nNOTE F F.— Par. 859-\n\nAll this was no doubt suggested by Heinrich Meyer,\nwhose chief occupation in Rome, at one time, was making\n\n♦ See Taylor's translation of Mcrimec on oil-pauiting, p. 27. Barry, in a\nletter from Parift, Hpealu of Restout as the only painter who resembled the\nearlier French masters : the maimer in qucbtion is undoubtedly sometimes\nvery observable in Pousbin. The Englibh artiht elsewhere speaks of the\n\" broad, happy manner of Subleyras, '—/#orit«, London, 1609.\n\nNOTES. 421\n\n■epia drawings from Knlpture (see Goethe's Italianische\nReise). It is hardly necessary to uj that the observation\nrespecting the treatment of the surface in the antique sta-\ntues is very fanciful.\n\nNOTE G G.— Par. 863.\nThis observation might have been suggested by the draw-\nings of Claude, which, with the slightest means, eidiibit an\nbarmomons balance of warm and cold.\n\nNOTE H H.— Par. 865.\nThe colouring of Paolo Uccello, according to Vasan*s\naccount of him, was occasionally so remarkable that he\nmight perhaps have been fairly included among the in-\nstances of defective vision given by the author. His skill in\nperspective, indicating an eye for gradation, may be also\nreckoned among the points of resemblance (see Par. 105).\n\nNOTE I I.— Par. 905.\nThe quotation before given from Boschini shows that\nthe method described by the author, and which is true with\nregard to some of the Florentine painters, was not prac-\ntised by the Venetians, for their first painting was very\nsolid. It agrees, however, with the manner of Rubens,\nmany of whose works sufficiently corroborate the account\nof his process given by Descamps. \" In the early state of\nRubens's pictures,\" says that writer,* \" everything appeared\nlike a thin wash ; but although he often made use of the\nground in producing his tones, the canvas was entirely\ncovered more or less with colour.\" In this system of leaving\nthe shadows transparent from the first, with the ground\nshining through them, it would have been obviously destruc-\ntive of richness to use white mixed with the darks, the\nbrightness, in fact, already existed underneath. Hence tbc\n\n422 MOTES.\n\nwell-tcnown precept of Rubens to avoid white in the sha-\ndows, a precept, like many others, beloi^puig to a particular\npractice, and involving all the conditions of that practice.*\nScarmiglione, whose Aristotelian treatise on colour was\npublished in Germany when Rubens was three-and-twenty,\nobserves, *^ Painters, with consummate art, lock up the\nbright colours with dark ones, and, on the other hand,\nemploy white, the poison of a picture, very sparingly.**\n(Artificiosissime pictores claros obscuris obsepiant et contra\ncandido picturarum veneno summe parcentes, &c.)\n\nNOTE K K.— Par. 903.\n\nThe practice here alluded to is more frequently observ-\nable in slight works by Paul Veronese. His ground was\noften pure white, and in some of his works it is left as such.\nTitian's white ground was covered with a light warm colour,\nprobably at firsts and aj^ars to have been similar to that\nto which Armenini gives the preference, namely, '^ quel la\nche tira al color di came chiarissima con un non so che di\nfiammeggiante.\"!\n\n* The method he recommended for keeping the colours pure in the lights,\nviz. to place the tints next each other unmixed, and then slightly to unite\nthem, may have d^enerated to a methodical manner in the hands of his fol-\nlowers. Boschini, who speaks of Rubens himself with due reverence, and\nis far from confounding him with his imitators, contrasts such a system\nwith that of the Venetians, and adds that Titian used to say, '' Chi do imhra-\ntar colori teme, imbrata e machia si medemi.\" — Carta del Savegar^ p. 341.\nThe poem of Boschini is in many respects polemical. He wrote at a time\nwhen the Flemish painters, having adopted and modified the Venetian prin-\nciples, threatened to supersede the Italian masters in the opinion of the\nworld. Their excellence, too, had all the charm of novelty, for in tlie seven-\nteenth century Venice produced no remarkable talent, and it was precisely\nthe age for her to boast of past glories. The contemptuous manner in which\nBoschini speaks of the Flemish varnishes, of the fear of mixing tints, &c., is\nthus always to be considered with reference to the time and circumstances.\nSo also his boasting that the Venetian masters painted without nature, which\nmay l>e an exaggeration, is pointed at the Naturalitti^ Caravaggio and his\nfollowers, who copietl nature literally.\n\nf \" Veri Precetti della Pittura,\" p. 125.\n\nNOTE L L— Par. 919-\nTbfl notion which the author has here ventured to express\nmay hare been suggested by the remarkable passage m the\nlast canto of Dante's \" Paradiso\" —\n\n\" Nella piofoDdK i chiare suniitnizs,\nDell' >lto lume puremi tra gin\nDi tte Golori e d*iui&cotitiiieiiia,\"&c.\n\nAfter the concluding paragraph the author inserts a letter\nfrom a landscape-painter, Pbilipp Otto Runge, which is\nintended to show that those who imitate nature may arrive\nat principles analt^ous to those of the \" Farbenlebre.\"\n\nLuuIob; PriDltd by W. Clovii ud Son, StuBbnl St\n\nk\n\nTHE UNIVERSITY OF MICHIGAN\n\nDATE DUE\n\nMfK b 1981\n\nJU^JC1521W87\n\nJUN 1 8 2002\n\n♦ /T-^^l\n\n'ii'.i;;'!:!\n\nI) l!r'\n\n3 9015 01159 5272\n\nDO\n\n^movE\n\nOR\n\nCARD",
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