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    "slug": "00-theory-of-colours",
    "title": "Theory of Colours",
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    "text": "## Theory of Colours\n\n*by Goethe (tr. Charles Lock Eastlake)*\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\n\n    \"Cicero varietatem propriè in coloribus nasci, hinc in\n    alienum migrare existimavit. Certè non alibi natura\n    copiosius aut majore lasciviâ opes suas commendavit.\n    Metalla, gemmas, marmora, flores, astra, omnia denique quæ\n    progenuit suis etiam coloribus distinxit; ut venia debeatur\n    si quis in tam numerosâ rerum sylvâ caligaverit.\"\n\n    CELIO CALCAGNINI.\n\nLONDON:\n\nJOHN MURRAY, ALBEMARLE STREET.\n\n1840\n\n\n\n\n\nTO\n\nJEREMIAH HARMAN, Esq.\n\n    Dear Sir,\n\n    I dedicate to you the following translation as a testimony\n    of my sincere gratitude and respect; in doing so, I but\n    follow the example of Portius, an Italian writer, who\n    inscribed his translation of Aristotle's Treatise on Colours\n    to one of the Medici.\n\n                     I have the honour to be,\n\n                        Dear Sir,\n\n                          Your most obliged and obedient Servant,\n\n                                                 C. L. EASTLAKE.\n\n\n\n\n## THE TRANSLATOR'S PREFACE.\n\n\n\nEnglish writers who have spoken of Goethe's \"Doctrine of Colours,\"[1]\nhave generally confined their remarks to those parts of the work in\nwhich he has undertaken to account for the colours of the prismatic\nspectrum, and of refraction altogether, on principles different\nfrom the received theory of Newton. The less questionable merits\nof the treatise consisting of a well-arranged mass of observations\nand experiments, many of which are important and interesting, have\nthus been in a great measure overlooked. The translator, aware of\nthe opposition which the theoretical views alluded to have met with,\nintended at first to make a selection of such of the experiments as\nseem more directly applicable to the theory and practice of painting.\nFinding, however, that the alterations this would have involved would\nhave been incompatible with a clear and connected view of the author's\nstatements, he preferred giving the theory itself entire, reflecting,\nat the same time, that some scientific readers may be curious to hear\nthe author speak for himself even on the points at issue.\n\nIn reviewing the history and progress of his opinions and researches,\nGoethe tells us that he first submitted his views to the public\nin two short essays entitled \"Contributions to Optics.\" Among the\ncircumstances which he supposes were unfavourable to him on that\noccasion, he mentions the choice of his title, observing that by a\nreference to optics he must have appeared to make pretensions to a\nknowledge of mathematics, a science with which he admits he was very\nimperfectly acquainted. Another cause to which he attributes the severe\ntreatment he experienced, was his having ventured so openly to question\nthe truth of the established theory: but this last provocation could\nnot be owing to mere inadvertence on his part; indeed the larger work,\nin which he alludes to these circumstances, is still more remarkable\nfor the violence of his objections to the Newtonian doctrine.\n\nThere can be no doubt, however, that much of the opposition Goethe met\nwith was to be attributed to the manner as well as to the substance\nof his statements. Had he contented himself with merely detailing his\nexperiments and showing their application to the laws of chromatic\nharmony, leaving it to others to reconcile them as they could with the\npre-established system, or even to doubt in consequence, the truth of\nsome of the Newtonian conclusions, he would have enjoyed the credit\nhe deserved for the accuracy and the utility of his investigations.\nAs it was, the uncompromising expression of his convictions only\nexposed him to the resentment or silent neglect of a great portion\nof the scientific world, so that for a time he could not even obtain\na fair hearing for the less objectionable or rather highly valuable\ncommunications contained in his book. A specimen of his manner of\nalluding to the Newtonian theory will be seen in the preface.\n\nIt was quite natural that this spirit should call forth a somewhat\nvindictive feeling, and with it not a little uncandid as well as\nunsparing criticism. \"The Doctrine of Colours\" met with this reception\nin Germany long before it was noticed in England, where a milder and\nfairer treatment could hardly be expected, especially at a time when,\nowing perhaps to the limited intercourse with the continent, German\nliterature was far less popular than it is at present. This last fact,\nit is true, can be of little importance in the present instance,\nfor although the change of opinion with regard to the genius of an\nenlightened nation must be acknowledged to be beneficial, it is to be\nhoped there is no fashion in science, and the translator begs to state\nonce for all, that in advocating the neglected merits of the \"Doctrine\nof Colours,\" he is far from undertaking to defend its imputed errors.\nSufficient time has, however, now elapsed since the publication of this\nwork (in 1810) to allow a calmer and more candid examination of its\nclaims. In this more pleasing task Germany has again for some time led\nthe way, and many scientific investigators have followed up the hints\nand observations of Goethe with a due acknowledgment of the acuteness\nof his views.[2]\n\nIt may require more magnanimity in English scientific readers to do\njustice to the merits of one who was so open and, in many respects, it\nis believed, so mistaken an opponent of Newton; but it must be admitted\nthat the statements of Goethe contain more useful principles in all\nthat relates to harmony of colour than any that have been derived from\nthe established doctrine. It is no derogation of the more important\ntruths of the Newtonian theory to say, that the views it contains\nseldom appear in a form calculated for direct application to the arts.\nThe principle of contrast, so universally exhibited in nature, so\napparent in the action and re-action of the eye itself, is scarcely\nhinted at. The equal pretensions of seven colours, as such, and the\nfanciful analogies which their assumed proportions could suggest, have\nrarely found favour with the votaries of taste,--indeed they have\nlong been abandoned even by scientific authorities.[3] And here the\ntranslator stops: he is quite aware that the defects which make the\nNewtonian theory so little available for æsthetic application, are\nfar from invalidating its more important conclusions in the opinion\nof most scientific men. In carefully abstaining therefore from any\ncomparison between the two theories in these latter respects, he may\nstill be permitted to advocate the clearness and fulness of Goethe's\nexperiments. The German philosopher reduces the colours to their\norigin and simplest elements; he sees and constantly bears in mind, and\nsometimes ably elucidates, the phenomena of contrast and gradation,\ntwo principles which may be said to make up the artist's world, and to\nconstitute the chief elements of beauty. These hints occur mostly in\nwhat may be called the scientific part of the work. On the other hand,\nin the portion expressly devoted to the æsthetic application of the\ndoctrine, the author seems to have made but an inadequate use of his\nown principles.\n\nIn that part of the chapter on chemical colours which relates to the\ncolours of plants and animals, the same genius and originality which\nare displayed in the Essays on Morphology, and which have secured\nto Goethe undisputed rank among the investigators of nature, are\nfrequently apparent.\n\nBut one of the most interesting features of Goethe's theory, although\nit cannot be a recommendation in a scientific point of view, is, that\nit contains, undoubtedly with very great improvements, the general\ndoctrine of the ancients and of the Italians at the revival of letters.\nThe translator has endeavoured, in some notes, to point out the\nconnexion between this theory and the practice of the Italian painters.\n\nThe \"Doctrine of Colours,\" as first published in 1810, consists of\ntwo volumes in 8vo., and sixteen plates, with descriptions, in 4to.\nIt is divided into three parts, a didactic, a controversial, and an\nhistorical part; the present translation is confined to the first of\nthese, with such extracts from the other two as seemed necessary,\nin fairness to the author, to explain some of his statements. The\npolemical and historical parts are frequently alluded to in the\npreface and elsewhere in the present work, but it has not been thought\nadvisable to omit these allusions. No alterations whatever seem to\nhave been made by Goethe in the didactic portion in later editions,\nbut he subsequently wrote an additional chapter on entoptic colours,\nexpressing his wish that it might be inserted in the theory itself at\na particular place which he points out. The form of this additional\nessay is, however, very different from that of the rest of the work,\nand the translator has therefore merely given some extracts from it in\nthe appendix. The polemical portion has been more than once omitted in\nlater editions.\n\nIn the two first parts the author's statements are arranged\nnumerically, in the style of Bacon's Natural History. This, we are\ntold, was for the convenience of reference; but many passages are\nthus separately numbered which hardly seem to have required it. The\nsame arrangement is, however, strictly followed in the translation to\nfacilitate a comparison with the original where it may be desired; and\nhere the translator observes, that although he has sometimes permitted\nhimself to make slight alterations, in order to avoid unnecessary\nrepetition, or to make the author's meaning clearer, he feels that an\napology may rather be expected from him for having omitted so little.\nHe was scrupulous on this point, having once determined to translate\nthe whole treatise, partly, as before stated, from a wish to deal\nfairly with a controversial writer, and partly because many passages,\nnot directly bearing on the scientific views, are still characteristic\nof Goethe. The observations which the translator has ventured to add\nare inserted in the appendix: these observations are chiefly confined\nto such of the author's opinions and conclusions as have direct\nreference to the arts; they seldom interfere with the scientific\npropositions, even where these have been considered most vulnerable.\n\n\n[1] \"Farbenlehre\"--in the present translation generally rendered\n\"Theory of Colours.\"\n\n[2] Sixteen years after the appearance of the Farbenlehre, Dr.\nJohannes Müller devoted a portion of his work, \"Zur vergleichenden\nPhysiologie des Gesichtssinnes des Menschen und der Thiere,\" to the\ncritical examination of Goethe's theory. In his introductory remarks he\nexpresses himself as follows--\"For my own part I readily acknowledge\nthat I have been greatly indebted to Goethe's treatise, and can truly\nsay that without having studied it for some years in connexion with the\nactual phenomena, the present work would hardly have been undertaken.\nI have no hesitation in confessing more particularly that I have full\nfaith in Goethe's statements, where they are merely descriptive of\nthe phenomena, and where the author does not enter into explanations\ninvolving a decision on the great points of controversy.\" The names of\nHegel, Schelling, Seebeck, Steffens, may also be mentioned, and many\nothers might be added, as authorities more or less favourable to the\nFarbenlehre.\n\n[3] \"When Newton attempted to reckon up the rays of light decomposed\nby the prism,\" says Sir John Leslie, \"and ventured to assign the\nfamous number _seven_, he was apparently influenced by some lurking\ndisposition towards mysticism. If any unprejudiced person will fairly\nrepeat the experiment, he must soon be convinced that the various\ncoloured spaces which paint the spectrum slide into each other by\nindefinite shadings: he may name four or five principal colours, but\nthe subordinate spaces are evidently so multiplied as to be incapable\nof enumeration. The same illustrious mathematician, we can hardly\ndoubt, was betrayed by a passion for analogy, when he imagined that the\nprimary 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 Subjects\nof Natural and Chemical Philosophy_, p. 59.\n\n\n\n\nPREFACE TO THE FIRST EDITION OF 1810.\n\n\nIt may naturally be asked whether, in proposing to treat of colours,\nlight itself should not first engage our attention: to this we briefly\nand frankly answer that since so much has already been said on the\nsubject of light, it can hardly be desirable to multiply repetitions by\nagain going over the same ground.\n\nIndeed, strictly speaking, it is useless to attempt to express the\nnature of a thing abstractedly. Effects we can perceive, and a complete\nhistory of those effects would, in fact, sufficiently define the\nnature of the thing itself. We should try in vain to describe a man's\ncharacter, but let his acts be collected and an idea of the character\nwill be presented to us.\n\nThe colours are acts of light; its active and passive modifications:\nthus considered we may expect from them some explanation respecting\nlight itself. Colours and light, it is true, stand in the most intimate\nrelation to each other, but we should think of both as belonging to\nnature as a whole, for it is nature as a whole which manifests itself\nby their means in an especial manner to the sense of sight.\n\nThe completeness of nature displays itself to another sense in a\nsimilar way. Let the eye be closed, let the sense of hearing be\nexcited, and from the lightest breath to the wildest din, from the\nsimplest sound to the highest harmony, from the most vehement and\nimpassioned cry to the gentlest word of reason, still it is Nature that\nspeaks and manifests her presence, her power, her pervading life and\nthe vastness of her relations; so that a blind man to whom the infinite\nvisible is denied, can still comprehend an infinite vitality by means\nof another organ.\n\nAnd thus as we descend the scale of being, Nature speaks to other\nsenses--to known, misunderstood, and unknown senses: so speaks she with\nherself and to us in a thousand modes. To the attentive observer she\nis nowhere dead nor silent; she has even a secret agent in inflexible\nmatter, in a metal, the smallest portions of which tell us what\nis passing in the entire mass. However manifold, complicated, and\nunintelligible this language may often seem to us, yet its elements\nremain ever the same. With light poise and counterpoise, Nature\noscillates within her prescribed limits, yet thus arise all the\nvarieties and conditions of the phenomena which are presented to us in\nspace and time.\n\nInfinitely various are the means by which we become acquainted with\nthese general movements and tendencies: now as a simple repulsion and\nattraction, now as an upsparkling and vanishing light, as undulation\nin the air, as commotion in matter, as oxydation and de-oxydation; but\nalways, uniting or separating, the great purpose is found to be to\nexcite and promote existence in some form or other.\n\nThe observers of nature finding, however, that this poise and\ncounterpoise are respectively unequal in effect, have endeavoured to\nrepresent such a relation in terms. They have everywhere remarked and\nspoken of a greater and lesser principle, an action and resistance,\na doing and suffering, an advancing and retiring, a violent and\nmoderating power; and thus a symbolical language has arisen, which,\nfrom its close analogy, may be employed as equivalent to a direct and\nappropriate terminology.\n\nTo apply these designations, this language of Nature to the subject\nwe have undertaken: to enrich and amplify this language by means of\nthe theory of colours and the variety of their phenomena, and thus\nfacilitate the communication of higher theoretical views, was the\nprincipal aim of the present treatise.\n\nThe work itself is divided into three parts. The first contains the\noutline of a theory of colours. In this, the innumerable cases which\npresent themselves to the observer are collected under certain leading\nphenomena, according to an arrangement which will be explained in\nthe Introduction; and here it may be remarked, that although we have\nadhered throughout to experiment, and throughout considered it as our\nbasis, yet the theoretical views which led to the arrangement alluded\nto, could not but be stated. It is sometimes unreasonably required by\npersons who do not even themselves attend to such a condition, that\nexperimental information should be submitted without any connecting\ntheory to the reader or scholar, who is himself to form his conclusions\nas he may list. Surely the mere inspection of a subject can profit us\nbut little. Every act of seeing leads to consideration, consideration\nto reflection, reflection to combination, and thus it may be said that\nin every attentive look on nature we already theorise. But in order to\nguard against the possible abuse of this abstract view, in order that\nthe practical deductions we look to should be really useful, we should\ntheorise without forgetting that we are so doing, we should theorise\nwith mental self-possession, and, to use a bold word, with irony.\n\nIn the second part[1] we examine the Newtonian theory; a theory which\nby its ascendancy and consideration has hitherto impeded a free inquiry\ninto the phenomena of colours. We combat that hypothesis, for although\nit is no longer found available, it still retains a traditional\nauthority in the world. Its real relations to its subject will require\nto be plainly pointed out; the old errors must be cleared away, if the\ntheory of colours is not still to remain in the rear of so many other\nbetter investigated departments of natural science. Since, however,\nthis second part of our work may appear somewhat dry as regards its\nmatter, and perhaps too vehement and excited in its manner, we may here\nbe permitted to introduce a sort of allegory in a lighter style, as a\nprelude to that graver portion, and as some excuse for the earnestness\nalluded to.\n\nWe compare the Newtonian theory of colours to an old castle, which\nwas at first constructed by its architect with youthful precipitation;\nit was, however, gradually enlarged and equipped by him according\nto the exigencies of time and circumstances, and moreover was still\nfurther fortified and secured in consequence of feuds and hostile\ndemonstrations.\n\nThe same system was pursued by his successors and heirs: their\nincreased wants within, the harassing vigilance of their opponents\nwithout, and various accidents compelled them in some places to build\nnear, in others in connexion with the fabric, and thus to extend the\noriginal plan.\n\nIt became necessary to connect all these incongruous parts and\nadditions by the strangest galleries, halls and passages. All damages,\nwhether inflicted by the hand of the enemy or the power of time, were\nquickly made good. As occasion required, they deepened the moats,\nraised the walls, and took care there should be no lack of towers,\nbattlements, and embrasures. This care and these exertions gave rise\nto a prejudice in favour of the great importance of the fortress,\nand still upheld that prejudice, although the arts of building and\nfortification were by this time very much advanced, and people had\nlearnt to construct much better dwellings and defences in other cases.\nBut the old castle was chiefly held in honour because it had never\nbeen taken, because it had repulsed so many assaults, had baffled so\nmany hostile operations, and had always preserved its virgin renown.\nThis renown, this influence lasts even now: it occurs to no one that\nthe old castle is become uninhabitable. Its great duration, its costly\nconstruction, are still constantly spoken of. Pilgrims wend their\nway to it; hasty sketches of it are shown in all schools, and it is\nthus recommended to the reverence of susceptible youth. Meanwhile,\nthe building itself is already abandoned; its only inmates are a few\ninvalids, who in simple seriousness imagine that they are prepared for\nwar.\n\nThus there is no question here respecting a tedious siege or a\ndoubtful war; so far from it we find this eighth wonder of the world\nalready nodding to its fall as a deserted piece of antiquity, and\nbegin at once, without further ceremony, to dismantle it from gable\nand roof downwards; that the sun may at last shine into the old nest\nof rats and owls, and exhibit to the eye of the wondering traveller\nthat labyrinthine, incongruous style of building, with its scanty,\nmake-shift contrivances, the result of accident and emergency, its\nintentional artifice and clumsy repairs. Such an inspection will,\nhowever, only be possible when wall after wall, arch after arch, is\ndemolished, the rubbish being at once cleared away as well as it can be.\n\nTo effect this, and to level the site where it is possible to do\nso, to arrange the materials thus acquired, so that they can be\nhereafter again employed for a new building, is the arduous duty\nwe have undertaken in this Second Part. Should we succeed, by a\ncheerful application of all possible ability and dexterity, in razing\nthis Bastille, and in gaining a free space, it is thus by no means\nintended at once to cover the site again and to encumber it with a new\nstructure; we propose rather to make use of this area for the purpose\nof passing in review a pleasing and varied series of illustrative\nfigures.\n\nThe third part is thus devoted to the historical account of early\ninquirers and investigators. As we before expressed the opinion that\nthe history of an individual displays his character, so it may here be\nwell affirmed that the history of science is science itself. We cannot\nclearly be aware of what we possess till we have the means of knowing\nwhat others possessed before us. We cannot really and honestly rejoice\nin the advantages of our own time if we know not how to appreciate\nthe advantages of former periods. But it was impossible to write, or\neven to prepare the way for a history of the theory of colours while\nthe Newtonian theory existed; for no aristocratic presumption has ever\nlooked down on those who were not of its order, with such intolerable\narrogance as that betrayed by the Newtonian school in deciding on\nall that had been done in earlier times and all that was done around\nit. With disgust and indignation we find Priestley, in his History\nof Optics, like many before and after him, dating the success of all\nresearches into the world of colours from the epoch of a decomposed ray\nof light, or what pretended to be so; looking down with a supercilious\nair on the ancient and less modern inquirers, who, after all, had\nproceeded quietly in the right road, and who have transmitted to us\nobservations and thoughts in detail which we can neither arrange better\nnor conceive more justly.\n\nWe have a right to expect from one who proposes to give the history of\nany science, that he inform us how the phenomena of which it treats\nwere gradually known, and what was imagined, conjectured, assumed,\nor thought respecting them. To state all this in due connexion is by\nno means an easy task; need we say that to write a history at all is\nalways a hazardous affair; with the most honest intention there is\nalways a danger of being dishonest; for in such an undertaking, a\nwriter tacitly announces at the outset that he means to place some\nthings in light, others in shade. The author has, nevertheless, long\nderived pleasure from the prosecution of his task: but as it is the\nintention only that presents itself to the mind as a whole, while the\nexecution is generally accomplished portion by portion, he is compelled\nto admit that instead of a history he furnishes only materials for\none. These materials consist in translations, extracts, original and\nborrowed comments, hints, and notes; a collection, in short, which, if\nnot answering all that is required, has at least the merit of having\nbeen made with earnestness and interest. Lastly, such materials,--not\naltogether untouched it is true, but still not exhausted,--may be more\nsatisfactory to the reflecting reader in the state in which they are,\nas he can easily combine them according to his own judgment.\n\nThis third part, containing the history of the science, does not,\nhowever, thus conclude the subject: a fourth supplementary portion[2]\nis added. This contains a recapitulation or revision; with a view\nto which, chiefly, the paragraphs are headed numerically. In the\nexecution of a work of this kind some things may be forgotten, some\nare of necessity omitted, so as not to distract the attention, some\ncan only be arrived at as corollaries, and others may require to be\nexemplified and verified: on all these accounts, postscripts, additions\nand corrections are indispensable. This part contains, besides, some\ndetached essays; for example, that on the atmospheric colours; for as\nthese are introduced in the theory itself without any classification,\nthey are here presented to the mind's eye at one view. Again, if this\nessay invites the reader to consult Nature herself, another is intended\nto recommend the artificial aids of science by circumstantially\ndescribing the apparatus which will in future be necessary to assist\nresearches into the theory of colours.\n\nIn conclusion, it only remains to speak of the plates which are added\nat the end of the work;[3] and here we confess we are reminded of that\nincompleteness and imperfection which the present undertaking has,\nin common with all others of its class; for as a good play can be in\nfact only half transmitted to writing, a great part of its effect\ndepending on the scene, the personal qualities of the actor, the powers\nof his voice, the peculiarities of his gestures, and even the spirit\nand favourable humour of the spectators; so it is, in a still greater\ndegree, with a book which treats of the appearances of nature. To be\nenjoyed, to be turned to account, Nature herself must be present to\nthe reader, either really, or by the help of a lively imagination.\nIndeed, the author should in such cases communicate his observations\norally, exhibiting the phenomena he describes--as a text, in the\nfirst instance,--partly as they appear to us unsought, partly as they\nmay be presented by contrivance to serve in particular illustration.\nExplanation and description could not then fail to produce a lively\nimpression.\n\nThe plates which generally accompany works like the present are thus\na most inadequate substitute for all this; a physical phenomenon\nexhibiting its effects on all sides is not to be arrested in lines\nnor denoted by a section. No one ever dreams of explaining chemical\nexperiments with figures; yet it is customary in physical researches\nnearly allied to these, because the object is thus found to be in\nsome degree answered. In many cases, however, such diagrams represent\nmere notions; they are symbolical resources, hieroglyphic modes of\ncommunication, which by degrees assume the place of the phenomena and\nof Nature herself, and thus rather hinder than promote true knowledge.\nIn the present instance we could not dispense with plates, but we have\nendeavoured so to construct them that they may be confidently referred\nto for the explanation of the didactic and polemical portions. Some of\nthese may even be considered as forming part of the apparatus before\nmentioned.\n\nWe now therefore refer the reader to the work itself; first, only\nrepeating a request which many an author has already made in vain, and\nwhich the modern German reader, especially, so seldom grants:--\n\n                Si quid novisti rectius istis\n    Candidus imperti; si non, his utere mecum.\n\n\n[1] The Polemical part.\n\n[2] This preface must have been written before the work was finished,\nfor at the conclusion of the historical part there is only an apology\nfor the non-appearance of the supplement here alluded to.\n\n[3] In the present translation the necessary plates accompany the\ntext.\n\n\n\n\nCONTENTS\n\n        Introduction xxxvii\n\n\n        PART I.\n\n        PHYSIOLOGICAL COLOURS.\n\n             I. Effects of Light and Darkness on the Eye\n            II. Effects of Black and White Objects on the Eye\n           III. Grey Surfaces and Objects\n            IV. Dazzling Colourless Objects\n             V. Coloured Objects\n            VI. Coloured Shadows\n           VII. Faint Lights\n          VIII. Subjective Halos\n                Pathological Colours--Appendix\n\n\n        PART II.\n\n        PHYSICAL COLOURS.\n\n             IX. Dioptrical Colours\n              X. Dioptrical Colours of the First Class\n             XI. Dioptrical Colours of the Second Class--Refraction\n                 Subjective Experiments\n            XII. Refraction without the Appearance of Colour\n           XIII. Conditions of the Appearance of Colour\n            XIV. Conditions under which the Appearance of Colour increases\n             XV. Explanation of the foregoing Phenomena\n            XVI. Decrease of the Appearance of Colour\n           XVII. Grey Objects displaced by Refraction\n          XVIII. Coloured Objects displaced by Refraction\n            XIX. Achromatism and Hyperchromatism\n             XX. Advantages of Subjective Experiments--\n                 Transition to the Objective\n                 Objective Experiments\n            XXI. Refraction without the Appearance of Colour\n           XXII. Conditions of the Appearance of Colour\n          XXIII. Conditions of the Increase of Colour\n           XXIV. Explanation of the foregoing Phenomena\n            XXV. Decrease of the Appearance of Colour\n           XXVI. Grey Objects\n          XXVII. Coloured Objects\n         XXVIII. Achromatism and Hyperchromatism\n           XXIX. Combination of Subjective and Objective Experiments\n            XXX. Transition\n           XXXI. Catoptrical Colours\n          XXXII. Paroptical Colours\n         XXXIII. Epoptical Colours\n\n\n        PART III.\n\n        CHEMICAL COLOURS.\n\n          XXXIV. Chemical Contrast\n           XXXV. White\n          XXXVI. Black\n         XXXVII. First Excitation of Colour\n        XXXVIII. Augmentation of Colour\n          XXXIX. Culmination\n             XL. Fluctuation\n            XLI. Passage through the Whole Scale\n           XLII. Inversion\n          XLIII. Fixation\n           XLIV. Intermixture, Real\n            XLV. Intermixture, Apparent\n           XLVI. Communication, Actual\n          XLVII. Communication, Apparent\n         XLVIII. Extraction\n           XLIX. Nomenclature\n              L. Minerals\n             LI. Plants\n            LII. Worms, Insects, Fishes\n           LIII. Birds\n            LIV. Mammalia and Human Beings\n             LV. Physical and Chemical Effects of the Transmission\n                 of Light through Coloured Mediums\n            LVI. Chemical Effect in Dioptrical Achromatism\n\n\n        PART IV.\n\n        GENERAL CHARACTERISTICS.\n\n        The Facility with which Colour appears\n        The Definite Nature of Colour\n        Combination of the Two Principles\n        Augmentation to Red\n        Junction of the Two Augmented Extremes\n        Completeness the Result of Variety in Colour\n        Harmony of the Complete State\n        Facility with which Colour may be made to tend either to\n        the Plus or Minus side\n        Evanescence of Colour\n        Permanence of Colour\n\n\n        PART V.\n\n        RELATION TO OTHER PURSUITS.\n\n        Relation to Philosophy\n        Relation to Mathematics\n        Relation to the Technical Operations of the Dyer\n        Relation to Physiology and Pathology\n        Relation to Natural History\n        Relation to General Physics\n        Relation to the Theory of Music\n        Concluding Observations on Terminology\n\n\n        PART VI.\n\n        EFFECT OF COLOUR WITH REFERENCE TO MORAL ASSOCIATIONS.\n\n        Yellow\n        Red-Yellow\n        Yellow-Red\n        Blue\n        Red-Blue\n        Blue-Red\n        Red\n        Green\n        Completeness and Harmony\n        Characteristic Combinations\n        Yellow and Blue\n        Yellow and Red\n        Blue and Red\n        Yellow-Red and Blue-Red\n        Combinations Non-Characteristic\n        Relation of the Combinations to Light and Dark\n        Considerations derived from the Evidence of Experience and History\n        Æsthetic Influence\n        Chiaro-Scuro\n        Tendency to Colour\n        Keeping\n        Colouring\n        Colour in General Nature\n        Colour of Particular Objects\n        Characteristic Colouring\n        Harmonious Colouring\n        Genuine Tone\n        False Tone\n        Weak Colouring\n        The Motley\n        Dread of Theory\n        Ultimate Aim\n        Grounds\n        Pigments\n        Allegorical, Symbolical, Mystical Application of Colour\n        Concluding Observations\n\n\n\n\nOUTLINE\n\nOF A\n\nTHEORY OF COLOURS.\n\n    \"Si vera nostra sunt aut falsa, erunt talia, licet nostra\n    per vitam defendimus. Post fata nostra pueri qui nunc ludunt\n    nostri judices erunt.\"\n\n\n\n\n## INTRODUCTION.\n\n\n\nThe desire of knowledge is first stimulated in us when remarkable\nphenomena attract our attention. In order that this attention be\ncontinued, it is necessary that we should feel some interest in\nexercising it, and thus by degrees we become better acquainted with the\nobject of our curiosity. During this process of observation we remark\nat first only a vast variety which presses indiscriminately on our\nview; we are forced to separate, to distinguish, and again to combine;\nby which means at last a certain order arises which admits of being\nsurveyed with more or less satisfaction.\n\nTo accomplish this, only in a certain degree, in any department,\nrequires an unremitting and close application; and we find, for this\nreason, that men prefer substituting a general theoretical view, or\nsome system of explanation, for the facts themselves, instead of taking\nthe trouble to make themselves first acquainted with cases in detail\nand then constructing a whole.\n\nThe attempt to describe and class the phenomena of colours has been\nonly twice made: first by Theophrastus,[1] and in modern times by\nBoyle. The pretensions of the present essay to the third place will\nhardly be disputed.\n\nOur historical survey enters into further details. Here we merely\nobserve that in the last century such a classification was not to be\nthought of, because Newton had based his hypothesis on a phenomenon\nexhibited in a complicated and secondary state; and to this the other\ncases that forced themselves on the attention were contrived to be\nreferred, when they could not be passed over in silence; just as an\nastronomer would do, if from whim he were to place the moon in the\ncentre of our system; he would be compelled to make the earth, sun, and\nplanets revolve round the lesser body, and be forced to disguise and\ngloss over the error of his first assumption by ingenious calculations\nand plausible statements.\n\nIn our prefatory observations we assumed the reader to be acquainted\nwith what was known respecting light; here we assume the same with\nregard to the eye. We observed that all nature manifests itself by\nmeans of colours to the sense of sight. We now assert, extraordinary as\nit may in some degree appear, that the eye sees no form, inasmuch as\nlight, shade, and colour together constitute that which to our vision\ndistinguishes object from object, and the parts of an object from each\nother. From these three, light, shade, and colour, we construct the\nvisible world, and thus, at the same time, make painting possible,\nan art which has the power of producing on a flat surface a much more\nperfect visible world than the actual one can be.\n\nThe eye may be said to owe its existence to light, which calls forth,\nas it were, a sense that is akin to itself; the eye, in short, is\nformed with reference to light, to be fit for the action of light; the\nlight it contains corresponding with the light without.\n\nWe are here reminded of a significant adage in constant use with the\nancient Ionian school--\"Like is only known by Like;\" and again, of the\nwords of an old mystic writer, which may be thus rendered, \"If the eye\nwere not sunny, how could we perceive light? If God's own strength\nlived not in us, how could we delight in Divine things?\" This immediate\naffinity between light and the eye will be denied by none; to consider\nthem as identical in substance is less easy to comprehend. It will be\nmore intelligible to assert that a dormant light resides in the eye,\nand that it may be excited by the slightest cause from within or from\nwithout. In darkness we can, by an effort of imagination, call up the\nbrightest images; in dreams objects appear to us as in broad daylight;\nawake, the slightest external action of light is perceptible, and if\nthe organ suffers an actual shock, light and colours spring forth.\nHere, however, those who are wont to proceed according to a certain\nmethod, may perhaps observe that as yet we have not decidedly explained\nwhat colour is. This question, like the definition of light and the\neye, we would for the present evade, and would appeal to our inquiry\nitself, where we have circumstantially shown how colour is produced.\nWe have only therefore to repeat that colour is a law of nature in\nrelation with the sense of sight. We must assume, too, that every one\nhas this sense, that every one knows the operation of nature on it, for\nto a blind man it would be impossible to speak of colours.\n\nThat we may not, however, appear too anxious to shun such an\nexplanation, we would restate what has been said as follows: colour is\nan elementary phenomenon in nature adapted to the sense of vision; a\nphenomenon which, like all others, exhibits itself by separation and\ncontrast, by commixture and union, by augmentation and neutralization,\nby communication and dissolution: under these general terms its nature\nmay be best comprehended.\n\nWe do not press this mode of stating the subject on any one. Those\nwho, like ourselves, find it convenient, will readily adopt it; but we\nhave no desire to enter the lists hereafter in its defence. From time\nimmemorial it has been dangerous to treat of colour; so much so, that\none of our predecessors ventured on a certain occasion to say, \"The ox\nbecomes furious if a red cloth is shown to him; but the philosopher,\nwho speaks of colour only in a general way, begins to rave.\"\n\nNevertheless, if we are to proceed to give some account of our work, to\nwhich we have appealed, we must begin by explaining how we have classed\nthe different conditions under which colour is produced. We found three\nmodes in which it appears; three classes of colours, or rather three\nexhibitions of them all. The distinctions of these classes are easily\nexpressed.\n\nThus, in the first instance, we considered colours, as far as they\nmay be said to belong to the eye itself, and to depend on an action\nand re-action of the organ; next, they attracted our attention as\nperceived in, or by means of, colourless mediums; and lastly, where\nwe could consider them as belonging to particular substances. We have\ndenominated the first, physiological, the second, physical, the third,\nchemical colours. The first are fleeting and not to be arrested; the\nnext are passing, but still for a while enduring; the last may be made\npermanent for any length of time.\n\nHaving separated these classes and kept them as distinct as possible,\nwith a view to a clear, didactic exposition, we have been enabled at\nthe same time to exhibit them in an unbroken series, to connect the\nfleeting with the somewhat more enduring, and these again with the\npermanent hues; and thus, after having carefully attended to a distinct\nclassification in the first instance, to do away with it again when a\nlarger view was desirable.\n\nIn a fourth division of our work we have therefore treated generally\nwhat was previously detailed under various particular conditions, and\nhave thus, in fact, given a sketch for a future theory of colours. We\nwill here only anticipate our statements so far as to observe, that\nlight and darkness, brightness and obscurity, or if a more general\nexpression is preferred, light and its absence, are necessary to the\nproduction of colour. Next to the light, a colour appears which we call\nyellow; another appears next to the darkness, which we name blue. When\nthese, in their purest state, are so mixed that they are exactly equal,\nthey produce a third colour called green. Each of the two first-named\ncolours can however of itself produce a new tint by being condensed or\ndarkened. They thus acquire a reddish appearance which can be increased\nto so great a degree that the original blue or yellow is hardly to\nbe recognised in it: but the intensest and purest red, especially in\nphysical cases, is produced when the two extremes of the yellow-red\nand blue-red are united. This is the actual state of the appearance\nand generation of colours. But we can also assume an existing red in\naddition to the definite existing blue and yellow, and we can produce\ncontrariwise, by mixing, what we directly produced by augmentation or\ndeepening. With these three or six colours, which may be conveniently\nincluded in a circle, the elementary doctrine of colours is alone\nconcerned. All other modifications, which may be extended to infinity,\nhave reference more to the application,--have reference to the\ntechnical operations of the painter and dyer, and the various purposes\nof artificial life. To point out another general quality, we may\nobserve that colours throughout are to be considered as half-lights, as\nhalf-shadows, on which account if they are so mixed as reciprocally to\ndestroy their specific hues, a shadowy tint, a grey, is produced.\n\nIn the fifth division of our inquiry we had proposed to point out\nthe relations in which we should wish our doctrine of colours to\nstand to other pursuits. Important as this part of our work is, it\nis perhaps on this very account not so successful as we could wish.\nYet when we reflect that strictly speaking these relations cannot be\ndescribed before they exist, we may console ourselves if we have in\nsome degree failed in endeavouring for the first time to define them.\nFor undoubtedly we should first wait to see how those whom we have\nendeavoured to serve, to whom we have intended to make an agreeable and\nuseful offering, how such persons, we say, will accept the result of\nour utmost exertion: whether they will adopt it, whether they will make\nuse of it and follow it up, or whether they will repel, reject, and\nsuffer it to remain unassisted and neglected.\n\nMeanwhile, we venture to express what we believe and hope. From the\nphilosopher we believe we merit thanks for having traced the phenomena\nof colours to their first sources, to the circumstances under which\nthey simply appear and are, and beyond which no further explanation\nrespecting them is possible. It will, besides, be gratifying to him\nthat we have arranged the appearances described in a form that admits\nof being easily surveyed, even should he not altogether approve of the\narrangement itself.\n\nThe medical practitioner, especially him whose study it is to watch\nover the organ of sight, to preserve it, to assist its defects and to\ncure its disorders, we reckon to make especially our friend. In the\nchapter on the physiological colours, in the Appendix relating to those\nthat are more strictly pathological, he will find himself quite in his\nown province. We are not without hopes of seeing the physiological\nphenomena,--a hitherto neglected, and, we may add, most important\nbranch of the theory of colours,--completely investigated through the\nexertions of those individuals who in our own times are treating this\ndepartment with success.\n\nThe investigator of nature should receive us cordially, since we\nenable him to exhibit the doctrine of colours in the series of other\nelementary phenomena, and at the same time enable him to make use of a\ncorresponding nomenclature, nay, almost the same words and designations\nas under the other rubrics. It is true we give him rather more trouble\nas a teacher, for the chapter of colours is not now to be dismissed\nas heretofore with a few paragraphs and experiments; nor will the\nscholar submit to be so scantily entertained as he has hitherto been,\nwithout murmuring. On the other hand, an advantage will afterwards\narise out of this: for if the Newtonian doctrine was easily learnt,\ninsurmountable difficulties presented themselves in its application.\nOur theory is perhaps more difficult to comprehend, but once known, all\nis accomplished, for it carries its application along with it.\n\nThe chemist who looks upon colours as indications by which he may\ndetect the more secret properties of material things, has hitherto\nfound much inconvenience in the denomination and description of\ncolours; nay, some have been induced after closer and nicer examination\nto look upon colour as an uncertain and fallacious criterion in\nchemical operations. Yet we hope by means of our arrangement and the\nnomenclature before alluded to, to bring colour again into credit,\nand to awaken the conviction that a progressive, augmenting, mutable\nquality, a quality which admits of alteration even to inversion, is not\nfallacious, but rather calculated to bring to light the most delicate\noperations of nature.\n\nIn looking a little further round us, we are not without fears\nthat we may fail to satisfy another class of scientific men. By an\nextraordinary combination of circumstances the theory of colours\nhas been drawn into the province and before the tribunal of the\nmathematician, a tribunal to which it cannot be said to be amenable.\nThis was owing to its affinity with the other laws of vision which the\nmathematician was legitimately called upon to treat. It was owing,\nagain, to another circumstance: a great mathematician had investigated\nthe theory of colours, and having been mistaken in his observations as\nan experimentalist, he employed the whole force of his talent to give\nconsistency to this mistake. Were both these circumstances considered,\nall misunderstanding would presently be removed, and the mathematician\nwould willingly co-operate with us, especially in the physical\ndepartment of the theory.\n\nTo the practical man, to the dyer, on the other hand, our labour must\nbe altogether acceptable; for it was precisely those who reflected on\nthe facts resulting from the operations of dyeing who were the least\nsatisfied with the old theory: they were the first who perceived the\ninsufficiency of the Newtonian doctrine. The conclusions of men are\nvery different according to the mode in which they approach a science\nor branch of knowledge; from which side, through which door they\nenter. The literally practical man, the manufacturer, whose attention\nis constantly and forcibly called to the facts which occur under his\neye, who experiences benefit or detriment from the application of his\nconvictions, to whom loss of time and money is not indifferent, who\nis desirous of advancing, who aims at equalling or surpassing what\nothers have accomplished,--such a person feels the unsoundness and\nerroneousness of a theory much sooner than the man of letters, in whose\neyes words consecrated by authority are at last equivalent to solid\ncoin; than the mathematician, whose formula always remains infallible,\neven although the foundation on which it is constructed may not square\nwith it. Again, to carry on the figure before employed, in entering\nthis theory from the side of painting, from the side of æsthetic[2]\ncolouring generally, we shall be found to have accomplished a\nmost thank-worthy office for the artist. In the sixth part we have\nendeavoured to define the effects of colour as addressed at once to\nthe eye and mind, with a view to making them more available for the\npurposes of art. Although much in this portion, and indeed throughout,\nhas been suffered to remain as a sketch, it should be remembered that\nall theory can in strictness only point out leading principles, under\nthe guidance of which, practice may proceed with vigour and be enabled\nto attain legitimate results.\n\n\n[1] The treatise to which the author alludes in more generally ascribed\nto Aristotle.--T.\n\n[2] Æsthetic--belonging to taste as mere internal sense, from\nαἰσθάνομαι, to feel; the word was first used by Wolf.--T.\n\n\n\n\n## PART I.\n\n\n\n## PHYSIOLOGICAL COLOURS.\n\n\n\n1.\n\nWe naturally place these colours first, because they belong altogether,\nor in a great degree, to the _subject_[1]--to the eye itself. They\nare the foundation of the whole doctrine, and open to our view the\nchromatic harmony on which so much difference of opinion has existed.\nThey have been hitherto looked upon as extrinsic and casual, as\nillusion and infirmity: their appearances have been known from ancient\ndate; but, as they were too evanescent to be arrested, they were\nbanished into the region of phantoms, and under this idea have been\nvery variously described.\n\n2.\n\nThus they are called _colores adventicii_ by Boyle; _imaginarii_ and\n_phantastici_ by Rizetti; by Buffon, _couleurs accidentelles_; by\nScherfer, _scheinfarben_ (apparent colours); _ocular illusions_ and\n_deceptions of sight_ by many; by Hamberger, _vitia fugitiva_; by\nDarwin, _ocular spectra_.\n\n3.\n\nWe have called them physiological because they belong to the eye in a\nhealthy state; because we consider them as the necessary conditions\nof vision; the lively alternating action of which, with reference to\nexternal objects and a principle within it, is thus plainly indicated.\n\n4.\n\nTo these we subjoin the pathological colours, which, like all\ndeviations from a constant law, afford a more complete insight into the\nnature of the physiological colours.\n\n\n## EFFECTS OF LIGHT AND DARKNESS ON THE EYE.\n\n\n\n5.\n\nThe retina, after being acted upon by light or darkness, is found to be\nin two different states, which are entirely opposed to each other.\n\n6.\n\nIf we keep the eyes open in a totally dark place, a certain sense of\nprivation is experienced. The organ is abandoned to itself; it retires\ninto itself. That stimulating and grateful contact is wanting by means\nof which it is connected with the external world, and becomes part of a\nwhole.\n\n7.\n\nIf we look on a white, strongly illumined surface, the eye is dazzled,\nand for a time is incapable of distinguishing objects moderately\nlighted.\n\n8.\n\nThe whole of the retina is acted on in each of these extreme states,\nand thus we can only experience one of these effects at a time. In\nthe one case (6) we found the organ in the utmost relaxation and\nsusceptibility; in the other (7) in an overstrained state, and scarcely\nsusceptible at all.\n\n9.\n\nIf we pass suddenly from the one state to the other, even without\nsupposing these to be the extremes, but only, perhaps, a change from\nbright to dusky, the difference is remarkable, and we find that the\neffects last for some time.\n\n10.\n\nIn passing from bright daylight to a dusky place we distinguish nothing\nat first: by degrees the eye recovers its susceptibility; strong eyes\nsooner than weak ones; the former in a minute, while the latter may\nrequire seven or eight minutes.\n\n11.\n\nThe fact that the eye is not susceptible to faint impressions of\nlight, if we pass from light to comparative darkness, has led to\ncurious mistakes in scientific observations. Thus an observer, whose\neyes required some time to recover their tone, was long under the\nimpression that rotten wood did not emit light at noon-day, even in a\ndark room. The fact was, he did not see the faint light, because he was\nin the habit of passing from bright sunshine to the dark room, and only\nsubsequently remained so long there that the eye had time to recover\nitself.\n\nThe same may have happened to Doctor Wall, who, in the daytime, even in\na dark room, could hardly perceive the electric light of amber.\n\nOur not seeing the stars by day, as well as the improved appearance of\npictures seen through a double tube, is also to be attributed to the\nsame cause.\n\n12.\n\nIf we pass from a totally dark place to one illumined by the sun, we\nare dazzled. In coming from a lesser degree of darkness to light that\nis not dazzling, we perceive all objects clearer and better: hence eyes\nthat have been in a state of repose are in all cases better able to\nperceive moderately distinct appearances.\n\nPrisoners who have been long confined in darkness acquire so great\na susceptibility of the retina, that even in the dark (probably a\ndarkness very slightly illumined) they can still distinguish objects.\n\n13.\n\nIn the act which we call seeing, the retina is at one and the same time\nin different and even opposite states. The greatest brightness, short\nof dazzling, acts near the greatest darkness. In this state we at once\nperceive all the intermediate gradations of _chiaro-scuro_, and all the\nvarieties of hues.\n\n14.\n\nWe will proceed in due order to consider and examine these elements of\nthe visible world, as well as the relation in which the organ itself\nstands to them, and for this purpose we take the simplest objects.\n\n\n[1] The German distinction between _subject_ and _object_ is so\ngenerally understood and adopted, that it is hardly necessary to\nexplain that the subject is the _individual_, in this case the\n_beholder_; the object, _all that is without him_.--T.\n\n\n\n\nII.\n\n\n## EFFECTS OF BLACK AND WHITE OBJECTS ON THE EYE.\n\n\n\n15.\n\nIn the same manner as the retina generally is affected by brightness\nand darkness, so it is affected by single bright or dark objects.\nIf light and dark produce different results on the whole retina, so\nblack and white objects seen at the same time produce the same states\ntogether which light and dark occasioned in succession.\n\n16.\n\nA dark object appears smaller than a bright one of the same size. Let\na white disk be placed on a black ground, and a black disk on a white\nground, both being exactly similar in size; let them be seen together\nat some distance, and we shall pronounce the last to be about a fifth\npart smaller than the other. If the black circle be made larger by so\nmuch, they will appear equal.[1]\n\n17.\n\nThus Tycho de Brahe remarked that the moon in conjunction (the darker\nstate) appears about a fifth part smaller than when in opposition\n(the bright full state). The first crescent appears to belong to a\nlarger disk than the remaining dark portion, which can sometimes be\ndistinguished at the period of the new moon. Black dresses make people\nappear smaller than light ones. Lights seen behind an edge make an\napparent notch in it. A ruler, behind which the flame of a light just\nappears, seems to us indented. The rising or setting sun appears to\nmake a notch in the horizon.\n\n[Illustration]\n\n18.\n\nBlack, as the equivalent of darkness, leaves the organ in a state of\nrepose; white, as the representative of light, excites it. We may,\nperhaps, conclude from the above experiment (16) that the unexcited\nretina, if left to itself, is drawn together, and occupies a less space\nthan in its active state, produced by the excitement of light.\n\nHence Kepler says very beautifully: \"Certum est vel in retinâ caussâ\npicturæ, vel in spiritibus caussâ impressionis, exsistere dilatationem\nlucidorum.\"--_Paralip. in Vitellionem_, p. 220. Scherfer expresses a\nsimilar conjecture.--Note A.\n\n19.\n\nHowever this may be, both impressions derived from such objects remain\nin the organ itself, and last for some time, even when the external\ncause is removed. In ordinary experience we scarcely notice this, for\nobjects are seldom presented to us which are very strongly relieved\nfrom each other, and we avoid looking at those appearances that dazzle\nthe sight. In glancing from one object to another, the succession of\nimages appears to us distinct; we are not aware that some portion of\nthe impression derived from the object first contemplated passes to\nthat which is next looked at.\n\n20.\n\nIf in the morning, on waking, when the eye is very susceptible, we look\nintently at the bars of a window relieved against the dawning sky, and\nthen shut our eyes or look towards a totally dark place, we shall see a\ndark cross on a light ground before us for some time.\n\n21.\n\nEvery image occupies a certain space on the retina, and of course a\ngreater or less space in proportion as the object is seen near or at a\ndistance. If we shut the eyes immediately after looking at the sun we\nshall be surprised to find how small the image it leaves appears.\n\n22.\n\nIf, on the other hand, we turn the open eye towards the side of a\nroom, and consider the visionary image in relation to other objects,\nwe shall always see it larger in proportion to the distance of the\nsurface on which it is thrown. This is easily explained by the laws of\nperspective, according to which a small object near covers a great one\nat a distance.\n\n23.\n\nThe duration of these visionary impressions varies with the powers\nor structure of the eye in different individuals, just as the time\nnecessary for the recovery of the tone of the retina varies in passing\nfrom brightness to darkness (10): it can be measured by minutes and\nseconds, indeed much more exactly than it could formerly have been\nby causing a lighted linstock to revolve rapidly, so as to appear a\ncircle.--Note B.\n\n24.\n\nBut the force with which an impinging light impresses the eye is\nespecially worthy of attention. The image of the sun lasts longest;\nother objects, of various degrees of brightness, leave the traces of\ntheir appearance on the eye for a proportionate time.\n\n25.\n\nThese images disappear by degrees, and diminish at once in distinctness\nand in size.\n\n26.\n\nThey are reduced from the contour inwards, and the impression on some\npersons has been that in square images the angles become gradually\nblunted till at last a diminished round image floats before the eye.\n\n27.\n\nSuch an image, when its impression is no more observable, can,\nimmediately after, be again revived on the retina by opening and\nshutting the eye, thus alternately exciting and resting it.\n\n28.\n\nImages may remain on the retina in morbid affections of the eye for\nfourteen, seventeen minutes, or even longer. This indicates extreme\nweakness of the organ, its inability to recover itself; while visions\nof persons or things which are the objects of love or aversion indicate\nthe connexion between sense and thought.\n\n29.\n\nIf, while the image of the window-bars before mentioned lasts, we\nlook upon a light grey surface, the cross will then appear light\nand the panes dark. In the first case (20) the image was like the\noriginal picture, so that the visionary impression also could continue\nunchanged; but in the present instance our attention is excited by a\ncontrary effect being produced. Various examples have been given by\nobservers of nature.\n\n30.\n\nThe scientific men who made observations in the Cordilleras saw a\nbright appearance round the shadows of their heads on some clouds. This\nexample is a case in point; for, while they fixed their eyes on the\ndark shadow, and at the same time moved from the spot, the compensatory\nlight image appeared to float round the real dark one. If we look at\na black disk on a light grey surface, we shall presently, by changing\nthe direction of the eyes in the slightest degree, see a bright halo\nfloating round the dark circle.\n\nA similar circumstance happened to myself: for while, as I sat in the\nopen air, I was talking to a man who stood at a little distance from me\nrelieved on a grey sky, it appeared to me, as I slightly altered the\ndirection of my eyes, after having for some time looked fixedly at him,\nthat his head was encircled with a dazzling light.\n\nIn the same way probably might be explained the circumstance that\npersons crossing dewy meadows at sunrise see a brightness round each\nother's heads[2]; the brightness in this case may be also iridescent,\nas the phenomena of refraction come into the account.\n\nThus again it has been asserted that the shadows of a balloon thrown on\nclouds were bordered with bright and somewhat variegated circles.\n\nBeccaria made use of a paper kite in some experiments on electricity.\nRound this kite appeared a small shining cloud varying in size; the\nsame brightness was even observed round part of the string. Sometimes\nit disappeared, and if the kite moved faster the light appeared to\nfloat to and fro for a few moments on the place before occupied. This\nappearance, which could not be explained by those who observed it at\nthe time, was the image which the eye retained of the kite relieved as\na dark mass on a bright sky; that image being changed into a light mass\non a comparatively dark background.\n\nIn optical and especially in chromatic experiments, where the observer\nhas to do with bright lights whether colourless or coloured, great care\nshould be taken that the spectrum which the eye retains in consequence\nof a previous observation does not mix with the succeeding one, and\nthus affect the distinctness and purity of the impression.\n\n31.\n\nThese appearances have been explained as follows: That portion of the\nretina on which the dark cross (29) was impressed is to be considered\nin a state of repose and susceptibility. On this portion therefore the\nmoderately light surface acted in a more lively manner than on the rest\nof the retina, which had just been impressed with the light through\nthe panes, and which, having thus been excited by a much stronger\nbrightness, could only view the grey surface as a dark.\n\n32.\n\nThis mode of explanation appears sufficient for the cases in question,\nbut, in the consideration of phenomena hereafter to be adduced, we are\nforced to trace the effects to higher sources.\n\n33.\n\nThe eye after sleep exhibits its vital elasticity more especially by\nits tendency to alternate its impressions, which in the simplest form\nchange from dark to light, and from light to dark. The eye cannot for a\nmoment remain in a particular state determined by the object it looks\nupon. On the contrary, it is forced to a sort of opposition, which, in\ncontrasting extreme with extreme, intermediate degree with intermediate\ndegree, at the same time combines these opposite impressions, and thus\never tends to a whole, whether the impressions are successive, or\nsimultaneous and confined to one image.\n\n34.\n\nPerhaps the peculiarly grateful sensation which we experience in\nlooking at the skilfully treated chiaro-scuro of colourless pictures\nand similar works of art arises chiefly from the _simultaneous_\nimpression of a whole, which by the organ itself is sought, rather than\narrived at, in _succession_, and which, whatever may be the result, can\nnever be arrested.\n\n\n[1] Plate 1. fig. 1.\n\n[2] See the Life of Benvenuto Cellini, vol. i. p. 453. Milan edition,\n1806.--T.\n\n\n\n\nIII.\n\n\n## GREY SURFACES AND OBJECTS.\n\n\n\n35.\n\nA moderate light is essential to many chromatic experiments. This can\nbe presently obtained by surfaces more or less grey, and thus we have\nat once to make ourselves acquainted with this simplest kind of middle\ntint, with regard to which it is hardly necessary to observe, that\nin many cases a white surface in shadow, or in a low light, may be\nconsidered equivalent to a grey.\n\n36.\n\nSince a grey surface is intermediate between brightness and darkness,\nit admits of our illustrating a phenomenon before described (29) by an\neasy experiment.\n\n37.\n\nLet a black object be held before a grey surface, and let the\nspectator, after looking steadfastly at it, keep his eyes unmoved while\nit is taken away: the space it occupied appears much lighter. Let a\nwhite object be held up in the same manner: on taking it away the space\nit occupied will appear much darker than the rest of the surface. Let\nthe spectator in both cases turn his eyes this way and that on the\nsurface, the visionary images will move in like manner.\n\n38.\n\nA grey object on a black ground appears much brighter than the same\nobject on a white ground. If both comparisons are seen together the\nspectator can hardly persuade himself that the two greys are identical.\nWe believe this again to be a proof of the great excitability of the\nretina, and of the silent resistance which every vital principle is\nforced to exhibit when any definite or immutable state is presented to\nit. Thus inspiration already presupposes expiration; thus every systole\nits diastole. It is the universal formula of life which manifests\nitself in this as in all other cases. When darkness is presented to\nthe eye it demands brightness, and _vice versâ_: it shows its vital\nenergy, its fitness to receive the impression of the object, precisely\nby spontaneously tending to an opposite state.\n\n\n\n\nIV.\n\n\n## DAZZLING COLOURLESS OBJECTS.\n\n\n\n39.\n\nIf we look at a dazzling, altogether colourless object, it makes a\nstrong lasting impression, and its after-vision is accompanied by an\nappearance of colour.\n\n40.\n\nLet a room be made as dark as possible; let there be a circular opening\nin the window-shutter about three inches in diameter, which may be\nclosed or not at pleasure. The sun being suffered to shine through this\non a white surface, let the spectator from some little distance fix his\neyes on the bright circle thus admitted. The hole being then closed,\nlet him look towards the darkest part of the room; a circular image\nwill now be seen to float before him. The middle of this circle will\nappear bright, colourless, or somewhat yellow, but the border will at\nthe same moment appear red.\n\nAfter a time this red, increasing towards the centre, covers the whole\ncircle, and at last the bright central point. No sooner, however, is\nthe whole circle red than the edge begins to be blue, and the blue\ngradually encroaches inwards on the red. When the whole is blue\nthe edge becomes dark and colourless. This darker edge again slowly\nencroaches on the blue till the whole circle appears colourless. The\nimage then becomes gradually fainter, and at the same time diminishes\nin size. Here again we see how the retina recovers itself by a\nsuccession of vibrations after the powerful external impression it\nreceived. (25, 26.)\n\n41.\n\nBy several repetitions similar in result, I found the comparative\nduration of these appearances in my own case to be as follows:--\n\nI looked on the bright circle five seconds, and then, having closed\nthe aperture, saw the coloured visionary circle floating before me.\nAfter thirteen seconds it was altogether red; twenty-nine seconds\nnext elapsed till the whole was blue, and forty-eight seconds till\nit appeared colourless. By shutting and opening the eye I constantly\nrevived the image, so that it did not quite disappear till seven\nminutes had elapsed.\n\nFuture observers may find these periods shorter or longer as their\neyes may be stronger or weaker (23), but it would be very remarkable\nif, notwithstanding such variations, a corresponding proportion as to\nrelative duration should be found to exist.\n\n42.\n\nBut this remarkable phenomenon no sooner excites our attention than we\nobserve a new modification of it.\n\nIf we receive the impression of the bright circle as before, and then\nlook on a light grey surface in a moderately lighted room, an image\nagain floats before us; but in this instance a dark one: by degrees it\nis encircled by a green border that gradually spreads inwards over the\nwhole circle, as the red did in the former instance. As soon as this\nhas taken place a dingy yellow appears, and, filling the space as the\nblue did before, is finally lost in a negative shade.\n\n43.\n\nThese two experiments may be combined by placing a black and a white\nplane surface next each other in a moderately lighted room, and then\nlooking alternately on one and the other as long as the impression of\nthe light circle lasts: the spectator will then perceive at first a red\nand green image alternately, and afterwards the other changes. After a\nlittle practice the two opposite colours may be perceived at once, by\ncausing the floating image to fall on the junction of the two planes.\nThis can be more conveniently done if the planes are at some distance,\nfor the spectrum then appears larger.\n\n44.\n\nI happened to be in a forge towards evening at the moment when a\nglowing mass of iron was placed on the anvil; I had fixed my eyes\nsteadfastly on it, and, turning round, I looked accidentally into an\nopen coal-shed: a large red image now floated before my eyes, and, as I\nturned them from the dark opening to the light boards of which the shed\nwas constructed, the image appeared half green, half red, according as\nit had a lighter or darker ground behind it. I did not at that time\ntake notice of the subsequent changes of this appearance.\n\n45.\n\nThe after-vision occasioned by a total dazzling of the retina\ncorresponds with that of a circumscribed bright object. The red colour\nseen by persons who are dazzled with snow belongs to this class of\nphenomena, as well as the singularly beautiful green colour which dark\nobjects seem to wear after looking long on white paper in the sun. The\ndetails of such experiments may be investigated hereafter by those\nwhose young eyes are capable of enduring such trials further for the\nsake of science.\n\n46.\n\nWith these examples we may also class the black letters which in the\nevening light appear red. Perhaps we might insert under the same\ncategory the story that drops of blood appeared on the table at which\nHenry IV. of France had seated himself with the Duc de Guise to play at\ndice.\n\n\n\n\nV.\n\n\n## COLOURED OBJECTS.\n\n\n\n47.\n\nWe have hitherto seen the physiological colours displayed in the\nafter-vision of colourless bright objects, and also in the after-vision\nof general colourless brightness; we shall now find analogous\nappearances if a given colour be presented to the eye: in considering\nthis, all that has been hitherto detailed must be present to our\nrecollection.\n\n48.\n\nThe impression of coloured objects remains in the eye like that of\ncolourless ones, but in this case the energy of the retina, stimulated\nas it is to produce the opposite colour, will be more apparent.\n\n49.\n\nLet a small piece of bright-coloured paper or silk stuff be held before\na moderately lighted white surface; let the observer look steadfastly\non the small coloured object, and let it be taken away after a time\nwhile his eyes remain unmoved; the spectrum of another colour will then\nbe visible on the white plane. The coloured paper may be also left in\nits place while the eye is directed to another part of the white plane;\nthe same spectrum will be visible there too, for it arises from an\nimage which now belongs to the eye.\n\n50.\n\nIn order at once to see what colour will be evoked by this contrast,\nthe chromatic circle[1] may be referred to. The colours are here\narranged in a general way according to the natural order, and the\narrangement will be found to be directly applicable in the present\ncase; for the colours diametrically opposed to each other in this\ndiagram are those which reciprocally evoke each other in the eye. Thus,\nyellow demands purple; orange, blue; red, green; and _vice versâ_: thus\nagain all intermediate gradations reciprocally evoke each other; the\nsimpler colour demanding the compound, and _vice versâ_.--Note C.\n\n51.\n\nThe cases here under consideration occur oftener than we are aware in\nordinary life; indeed, an attentive observer sees these appearances\neverywhere, while, on the other hand, the uninstructed, like our\npredecessors, consider them as temporary visual defects, sometimes\neven as symptoms of disorders in the eye, thus exciting serious\napprehensions. A few remarkable instances may here be inserted.\n\n52.\n\nI had entered an inn towards evening, and, as a well-favoured girl,\nwith a brilliantly fair complexion, black hair, and a scarlet bodice,\ncame into the room, I looked attentively at her as she stood before me\nat some distance in half shadow. As she presently afterwards turned\naway, I saw on the white wall, which was now before me, a black face\nsurrounded with a bright light, while the dress of the perfectly\ndistinct figure appeared of a beautiful sea-green.\n\n53.\n\nAmong the materials for optical experiments, there are portraits with\ncolours and shadows exactly opposite to the appearance of nature. The\nspectator, after having looked at one of these for a time, will see the\nvisionary figure tolerably true to nature. This is conformable to the\nsame principles, and consistent with experience, for, in the former\ninstance, a negress with a white head-dress would have given me a\nwhite face surrounded with black. In the case of the painted figures,\nhowever, which are commonly small, the parts are not distinguishable by\nevery one in the after-image.\n\n54.\n\nA phenomenon which has before excited attention among the observers of\nnature is to be attributed, I am persuaded, to the same cause.\n\nIt has been stated that certain flowers, towards evening in summer,\ncoruscate, become phosphorescent, or emit a momentary light. Some\npersons have described their observation of this minutely. I had often\nendeavoured to witness it myself, and had even resorted to artificial\ncontrivances to produce it.\n\nOn the 19th of June, 1799, late in the evening, when the twilight was\ndeepening into a clear night, as I was walking up and down the garden\nwith a friend, we very distinctly observed a flame-like appearance\nnear the oriental poppy, the flowers of which are remarkable for their\npowerful red colour. We approached the place and looked attentively\nat the flowers, but could perceive nothing further, till at last, by\npassing and repassing repeatedly, while we looked sideways on them, we\nsucceeded in renewing the appearance as often as we pleased. It proved\nto be a physiological phenomenon, such as others we have described, and\nthe apparent coruscation was nothing but the spectrum of the flower in\nthe compensatory blue-green colour.\n\nIn looking directly at a flower the image is not produced, but it\nappears immediately as the direction of the eye is altered. Again, by\nlooking sideways on the object, a double image is seen for a moment,\nfor the spectrum then appears near and on the real object.\n\nThe twilight accounts for the eye being in a perfect state of repose,\nand thus very susceptible, and the colour of the poppy is sufficiently\npowerful in the summer twilight of the longest days to act with\nfull effect and produce a compensatory image. I have no doubt these\nappearances might be reduced to experiment, and the same effect\nproduced by pieces of coloured paper. Those who wish to take the most\neffectual means for observing the appearance in nature--suppose in a\ngarden--should fix the eyes on the bright flowers selected for the\npurpose, and, immediately after, look on the gravel path. This will\nbe seen studded with spots of the opposite colour. The experiment is\npracticable on a cloudy day, and even in the brightest sunshine, for\nthe sun-light, by enhancing the brilliancy of the flower, renders it\nfit to produce the compensatory colour sufficiently distinct to be\nperceptible even in a bright light. Thus, peonies produce beautiful\ngreen, marigolds vivid blue spectra.\n\n55.\n\nAs the opposite colour is produced by a constant law in experiments\nwith coloured objects on portions of the retina, so the same effect\ntakes place when the whole retina is impressed with a single colour. We\nmay convince ourselves of this by means of coloured glasses. If we look\nlong through a blue pane of glass, everything will afterwards appear\nin sunshine to the naked eye, even if the sky is grey and the scene\ncolourless. In like manner, in taking off green spectacles, we see all\nobjects in a red light. Every decided colour does a certain violence to\nthe eye, and forces the organ to opposition.\n\n56.\n\nWe have hitherto seen the opposite colours producing each other\nsuccessively on the retina: it now remains to show by experiment\nthat the same effects can exist simultaneously. If a coloured object\nimpinges on one part of the retina, the remaining portion at the same\nmoment has a tendency to produce the compensatory colour. To pursue\na former experiment, if we look on a yellow piece of paper placed\non a white surface, the remaining part of the organ has already a\ntendency to produce a purple hue on the colourless surface: in this\ncase the small portion of yellow is not powerful enough to produce\nthis appearance distinctly, but, if a white paper is placed on a yellow\nwall, we shall see the white tinged with a purple hue.\n\n57.\n\nAlthough this experiment may be made with any colours, yet red and\ngreen are particularly recommended for it, because these colours seem\npowerfully to evoke each other. Numerous instances occur in daily\nexperience. If a green paper is seen through striped or flowered\nmuslin, the stripes or flowers will appear reddish. A grey building\nseen through green pallisades appears in like manner reddish. A\nmodification of this tint in the agitated sea is also a compensatory\ncolour: the light side of the waves appears green in its own colour,\nand the shadowed side is tinged with the opposite hue. The different\ndirection of the waves with reference to the eye produces the same\neffect. Objects seen through an opening in a red or green curtain\nappear to wear the opposite hue. These appearances will present\nthemselves to the attentive observer on all occasions, even to an\nunpleasant degree.\n\n58.\n\nHaving made ourselves acquainted with the simultaneous exhibition of\nthese effects in direct cases, we shall find that we can also observe\nthem by indirect means. If we place a piece of paper of a bright\norange colour on the white surface, we shall, after looking intently\nat it, scarcely perceive the compensatory colour on the rest of the\nsurface: but when we take the orange paper away, and when the blue\nspectrum appears in its place, immediately as this spectrum becomes\nfully apparent, the rest of the surface will be overspread, as if by a\nflash, with a reddish-yellow light, thus exhibiting to the spectator\nin a lively manner the productive energy of the organ, in constant\nconformity with the same law.\n\n59.\n\nAs the compensatory colours easily appear, where they do not exist in\nnature, near and after the original opposite ones, so they are rendered\nmore intense where they happen to mix with a similar real hue. In a\ncourt which was paved with grey limestone flags, between which grass\nhad grown, the grass appeared of an extremely beautiful green when\nthe evening clouds threw a scarcely perceptible reddish light on the\npavement. In an opposite case we find, in walking through meadows,\nwhere we see scarcely anything but green, the stems of trees and the\nroads often gleam with a reddish hue. This tone is not uncommon in\nthe works of landscape painters, especially those who practice in\nwater-colours: they probably see it in nature, and thus, unconsciously\nimitating it, their colouring is criticised as unnatural.\n\n60.\n\nThese phenomena are of the greatest importance, since they direct our\nattention to the laws of vision, and are a necessary preparation for\nfuture observations on colours. They show that the eye especially\ndemands completeness, and seeks to eke out the colorific circle in\nitself. The purple or violet colour suggested by yellow contains red\nand blue; orange, which responds to blue, is composed of yellow and\nred; green, uniting blue and yellow, demands red; and so through all\ngradations of the most complicated combinations. That we are compelled\nin this case to assume three leading colours has been already remarked\nby other observers.\n\n61.\n\nWhen in this completeness the elements of which it is composed are\nstill appreciable by the eye, the result is justly called harmony. We\nshall subsequently endeavour to show how the theory of the harmony of\ncolours may be deduced from these phenomena, and how, simply through\nthese qualities, colours may be capable of being applied to æsthetic\npurposes. This will be shown when we have gone through the whole circle\nof our observations, returning to the point from which we started.\n\n\n[1] Plate 1, fig. 3.\n\n\n\n\nVI.\n\n\n## COLOURED SHADOWS.\n\n\n\n62.\n\nBefore, however, we proceed further, we have yet to observe some very\nremarkable cases of the vivacity with which the suggested colours\nappear in the neighbourhood of others: we allude to coloured shadows.\nTo arrive at these we first turn our attention to shadows that are\ncolourless or negative.\n\n63.\n\nA shadow cast by the sun, in its full brightness, on a white surface,\ngives us no impression of colour; it appears black, or, if a contrary\nlight (here assumed to differ only in degree) can act upon it, it is\nonly weaker, half-lighted, grey.\n\n64.\n\nTwo conditions are necessary for the existence of coloured shadows:\nfirst, that the principal light tinge the white surface with some hue;\nsecondly, that a contrary light illumine to a certain extent the cast\nshadow.\n\n65.\n\nLet a short, lighted candle be placed at twilight on a sheet of white\npaper. Between it and the declining daylight let a pencil be placed\nupright, so that its shadow thrown by the candle may be lighted, but\nnot overcome, by the weak daylight: the shadow will appear of the most\nbeautiful blue.\n\n66.\n\nThat this shadow is blue is immediately evident; but we can only\npersuade ourselves by some attention that the white paper acts as a\nreddish yellow, by means of which the complemental blue is excited in\nthe eye.--Note D.\n\n67.\n\nIn all coloured shadows, therefore, we must presuppose a colour excited\nor suggested by the hue of the surface on which the shadow is thrown.\nThis may be easily found to be the case by attentive consideration, but\nwe may convince ourselves at once by the following experiment.\n\n68.\n\nPlace two candles at night opposite each other on a white surface; hold\na thin rod between them upright, so that two shadows be cast by it;\ntake a coloured glass and hold it before one of the lights, so that\nthe white paper appear coloured; at the same moment the shadow cast by\nthe coloured light and slightly illumined by the colourless one will\nexhibit the complemental hue.\n\n69.\n\nAn important consideration suggests itself here, to which we shall\nfrequently have occasion to return. Colour itself is a degree of\ndarkness _σκιερόν_; hence Kircher is perfectly right in calling it\n_lumen opacatum_. As it is allied to shadow, so it combines readily\nwith it; it appears to us readily in and by means of shadow the\nmoment a suggesting cause presents itself. We could not refrain from\nadverting at once to a fact which we propose to trace and develop\nhereafter.--Note E.\n\n70.\n\nSelect the moment in twilight when the light of the sky is still\npowerful enough to cast a shadow which cannot be entirely effaced by\nthe light of a candle. The candle may be so placed that a double shadow\nshall be visible, one from the candle towards the daylight, and another\nfrom the daylight towards the candle. If the former is blue the latter\nwill appear orange-yellow: this orange-yellow is in fact, however, only\nthe yellow-red light of the candle diffused over the whole paper, and\nwhich _becomes visible in shadow_.\n\n71.\n\nThis is best exemplified by the former experiment with two candles and\ncoloured glasses.\n\nThe surprising readiness with which shadow assumes a colour will again\ninvite our attention in the further consideration of reflections and\nelsewhere.\n\n72.\n\nThus the phenomena of coloured shadows may be traced to their cause\nwithout difficulty. Henceforth let any one who sees an instance of\nthe kind observe only with what hue the light surface on which they\nare thrown is tinged. Nay, the colour of the shadow may be considered\nas a chromatoscope of the illumined surface, for the spectator may\nalways assume the colour of the light to be the opposite of that of the\nshadow, and by an attentive examination may ascertain this to be the\nfact in every instance.\n\n73.\n\nThese appearances have been a source of great perplexity to former\nobservers: for, as they were remarked chiefly in the open air, where\nthey commonly appeared blue, they were attributed to a certain inherent\nblue or blue colouring quality in the air. The inquirer can, however,\nconvince himself, by the experiment with the candle in a room, that no\nkind of blue light or reflection is necessary to produce the effect\nin question. The experiment may be made on a cloudy day with white\ncurtains drawn before the light, and in a room where no trace of blue\nexists, and the blue shadow will be only so much the more beautiful.\n\n74.\n\nDe Saussure, in the description of his ascent of Mont Blanc, says, \"A\nsecond remark, which may not be uninteresting, relates to the colour of\nthe shadows. These, notwithstanding the most attentive observation, we\nnever found dark blue, although this had been frequently the case in\nthe plain. On the contrary, in fifty-nine instances we saw them once\nyellowish, six times pale bluish, eighteen times colourless or black,\nand thirty-four times pale violet. Some natural philosophers suppose\nthat these colours arise from accidental vapours diffused in the air,\nwhich communicate their own hues to the shadows; not that the colours\nof the shadows are occasioned by the reflection of any given sky colour\nor interposition of any given air colour: the above observations seem\nto favour this opinion.\" The instances given by De Saussure may be now\nexplained and classed with analogous examples without difficulty.\n\nAt a great elevation the sky was generally free from vapours, the sun\nshone in full force on the snow, so that it appeared perfectly white\nto the eye: in this case they saw the shadows quite colourless. If the\nair was charged with a certain degree of vapour, in consequence of\nwhich the light snow would assume a yellowish tone, the shadows were\nviolet-coloured, and this effect, it appears, occurred oftenest. They\nsaw also bluish shadows, but this happened less frequently; and that\nthe blue and violet were pale was owing to the surrounding brightness,\nby which the strength of the shadows was mitigated. Once only they\nsaw the shadow yellowish: in this case, as we have already seen (70),\nthe shadow is cast by a colourless light, and slightly illumined by a\ncoloured one.\n\n75.\n\nIn travelling over the Harz in winter, I happened to descend from the\nBrocken towards evening; the wide slopes extending above and below me,\nthe heath, every insulated tree and projecting rock, and all masses of\nboth, were covered with snow or hoar-frost. The sun was sinking towards\nthe Oder ponds[1]. During the day, owing to the yellowish hue of the\nsnow, shadows tending to violet had already been observable; these\nmight now be pronounced to be decidedly blue, as the illumined parts\nexhibited a yellow deepening to orange.\n\nBut as the sun at last was about to set, and its rays, greatly\nmitigated by the thicker vapours, began to diffuse a most beautiful\nred colour over the whole scene around me, the shadow colour changed\nto a green, in lightness to be compared to a sea-green, in beauty to\nthe green of the emerald. The appearance became more and more vivid:\none might have imagined oneself in a fairy world, for every object had\nclothed itself in the two vivid and so beautifully harmonising colours,\ntill at last, as the sun went down, the magnificent spectacle was lost\nin a grey twilight, and by degrees in a clear moon-and-starlight night.\n\n76.\n\nOne of the most beautiful instances of coloured shadows may be\nobserved during the full moon. The candle-light and moon-light may be\ncontrived to be exactly equal in force; both shadows may be exhibited\nwith equal strength and clearness, so that both colours balance each\nother perfectly. A white surface being placed opposite the full moon,\nand the candle being placed a little on one side at a due distance,\nan opaque body is held before the white plane, A double shadow will\nthen be seen: that cast by the moon and illumined by the candle-light\nwill be a powerful red-yellow; and contrariwise, that cast by the\ncandle and illumined by the moon will appear of the most beautiful\nblue. The shadow, composed of the union of the two shadows, where\nthey cross each other, is black. The yellow shadow (74) cannot perhaps\nbe exhibited in a more striking manner. The immediate vicinity of\nthe blue and the interposing black shadow make the appearance the\nmore agreeable. It will even be found, if the eye dwells long on\nthese colours, that they mutually evoke and enhance each other, the\nincreasing red in the one still producing its contrast, viz. a kind of\nsea-green.\n\n77.\n\nWe are here led to remark that in this, and in all cases, a moment or\ntwo may perhaps be necessary to produce the complemental colour. The\nretina must be first thoroughly impressed with the demanding hue before\nthe responding one can be distinctly observable.\n\n78.\n\nWhen divers are under water, and the sunlight shines into the\ndiving-bell, everything is seen in a red light (the cause of which\nwill be explained hereafter), while the shadows appear green. The very\nsame phenomenon which I observed on a high mountain (75) is presented\nto others in the depths of the sea, and thus Nature throughout is in\nharmony with herself.\n\n79.\n\nSome observations and experiments which equally illustrate what has\nbeen stated with regard to coloured objects and coloured shadows may\nbe here added. Let a white paper blind be fastened inside the window\non a winter evening; in this blind let there be an opening, through\nwhich the snow of some neighbouring roof can be seen. Towards dusk let\na candle be brought into the room; the snow seen through the opening\nwill then appear perfectly blue, because the paper is tinged with warm\nyellow by the candle-light. The snow seen through the aperture is here\nequivalent to a shadow illumined by a contrary light (76), and may also\nrepresent a grey disk on a coloured surface (56).\n\n80.\n\nAnother very interesting experiment may conclude these examples. If we\ntake a piece of green glass of some thickness, and hold it so that the\nwindow bars be reflected in it, they will appear double owing to the\nthickness of the glass. The image which is reflected from the under\nsurface of the glass will be green; the image which is reflected from\nthe upper surface, and which should be colourless, will appear red.\n\nThe experiment may be very satisfactorily made by pouring water into\na vessel, the inner surface of which can act as a mirror; for both\nreflections may first be seen colourless while the water is pure, and\nthen by tinging it, they will exhibit two opposite hues.\n\n\n[1] Reservoirs in which water is collected from various small streams,\nto work the mines.--T.\n\n\n\n\nVII.\n\n\n## FAINT LIGHTS.\n\n\n\n81.\n\nLight, in its full force, appears purely white, and it gives this\nimpression also in its highest degree of dazzling splendour. Light,\nwhich is not so powerful, can also, under various conditions, remain\ncolourless. Several naturalists and mathematicians have endeavoured to\nmeasure its degrees--Lambert, Bouguer, Rumford.\n\n82.\n\nYet an appearance of colour presently manifests itself in fainter\nlights, for in their relation to absolute light they resemble the\ncoloured spectra of dazzling objects (39).\n\n83.\n\nA light of any kind becomes weaker, either when its own force, from\nwhatever cause, is diminished, or when the eye is so circumstanced or\nplaced, that it cannot be sufficiently impressed by the action of the\nlight. Those appearances which may be called objective, come under the\nhead of physical colours. We will only advert here to the transition\nfrom white to red heat in glowing iron. We may also observe that the\nflames of lights at night appear redder in proportion to their distance\nfrom the eye.--Note F.\n\n84.\n\nCandle-light at night acts as yellow when seen near; we can perceive\nthis by the effect it produces on other colours. At night a pale yellow\nis hardly to be distinguished from white; blue approaches to green, and\nrose-colour to orange.\n\n85.\n\nCandle-light at twilight acts powerfully as a yellow light: this\nis best proved by the purple blue shadows which, under these\ncircumstances, are evoked by the eye.\n\n86.\n\nThe retina may be so excited by a strong light that it cannot perceive\nfainter lights (11): if it perceive these they appear coloured: hence\ncandle-light by day appears reddish, thus resembling, in its relation\nto fuller light, the spectrum of a dazzling object; nay, if at night we\nlook long and intently on the flame of a light, it appears to increase\nin redness.\n\n87.\n\nThere are faint lights which, notwithstanding their moderate lustre,\ngive an impression of a white, or, at the most, of a light yellow\nappearance on the retina; such as the moon in its full splendour.\nRotten wood has even a kind of bluish light. All this will hereafter be\nthe subject of further remarks.\n\n88.\n\nIf at night we place a light near a white or greyish wall so that the\nsurface be illumined from this central point to some extent, we find,\non observing the spreading light at some distance, that the boundary of\nthe illumined surface appears to be surrounded with a yellow circle,\nwhich on the outside tends to red-yellow. We thus observe that when\nlight direct or reflected does not act in its full force, it gives an\nimpression of yellow, of reddish, and lastly even of red. Here we find\nthe transition to halos which we are accustomed to see in some mode or\nother round luminous points.\n\n\n\n\n## VIII.\n\n\n\n## SUBJECTIVE HALOS.\n\n\n\n89.\n\nHalos may be divided into subjective and objective. The latter will\nbe considered under the physical colours; the first only belong here.\nThese are distinguished from the objective halos by the circumstance\nof their vanishing when the point of light which produces them on the\nretina is covered.\n\n90.\n\nWe have before noticed the impression of a luminous object on the\nretina, and seen that it appears larger: but the effect is not at\nan end here, it is not confined to the impression of the image; an\nexpansive action also takes place, spreading from the centre.\n\n91.\n\nThat a nimbus of this kind is produced round the luminous image in the\neye may be best seen in a dark room, if we look towards a moderately\nlarge opening in the window-shutter. In this case the bright image is\nsurrounded by a circular misty light. I saw such a halo bounded by a\nyellow and yellow-red circle on opening my eyes at dawn, on an occasion\nwhen I passed several nights in a bed-carriage.\n\n92.\n\nHalos appear most vivid when the eye is susceptible from having been in\na state of repose. A dark background also heightens their appearance.\nBoth causes account for our seeing them so strong if a light is\npresented to the eyes on waking at night. These conditions were\ncombined when Descartes after sleeping, as he sat in a ship, remarked\nsuch a vividly-coloured halo round the light.\n\n93.\n\nA light must shine moderately, not dazzle, in order to produce the\nimpression of a halo in the eye; at all events the halos of dazzling\nlights cannot be observed. We see a splendour of this kind round the\nimage of the sun reflected from the surface of water.\n\n94.\n\nA halo of this description, attentively observed, is found to be\nencircled towards its edge with a yellow border: but even here the\nexpansive action, before alluded to, is not at an end, but appears\nstill to extend in varied circles.\n\n95.\n\nSeveral cases seem to indicate a circular action of the retina, whether\nowing to the round form of the eye itself and its different parts, or\nto some other cause.\n\n96.\n\nIf the eye is pressed only in a slight degree from the inner corner,\ndarker or lighter circles appear. At night, even without pressure, we\ncan sometimes perceive a succession of such circles emerging from, or\nspreading over, each other.\n\n97.\n\nWe have already seen that a yellow border is apparent round the white\nspace illumined by a light placed near it. This may be a kind of\nobjective halo. (88.)\n\n98.\n\nSubjective halos may be considered as the result of a conflict between\nthe light and a living surface. From the conflict between the exciting\nprinciple and the excited, an undulating motion arises, which may be\nillustrated by a comparison with the circles on water. The stone thrown\nin drives the water in all directions; the effect attains a maximum,\nit reacts, and being opposed, continues under the surface. The effect\ngoes on, culminates again, and thus the circles are repeated. If we\nhave ever remarked the concentric rings which appear in a glass of\nwater on trying to produce a tone by rubbing the edge; if we call to\nmind the intermitting pulsations in the reverberations of bells, we\nshall approach a conception of what may take place on the retina when\nthe image of a luminous object impinges on it, not to mention that as\na living and elastic structure, it has already a circular principle in\nits organisation.--Note G.\n\n99.\n\nThe bright circular space which appears round the shining object\nis yellow, ending in red: then follows a greenish circle, which is\nterminated by a red border. This appears to be the usual phenomenon\nwhere the luminous body is somewhat considerable in size. These halos\nbecome greater the more distant we are from the luminous object.\n\n100.\n\nHalos may, however, appear extremely small and numerous when the\nimpinging image is minute, yet powerful, in its effect. The experiment\nis best made with a piece of gold-leaf placed on the ground and\nillumined by the sun. In these cases the halos appear in variegated\nrays. The iridescent appearance produced in the eye when the sun\npierces through the leaves of trees seems also to belong to the same\nclass of phenomena.\n\n\n\n\n## PATHOLOGICAL COLOURS.\n\n\n\n## APPENDIX.\n\n\n\n101.\n\nWe are now sufficiently acquainted with the physiological colours to\ndistinguish them from the pathological. We know what appearances belong\nto the eye in a healthy state, and are necessary to enable the organ to\nexert its complete vitality and activity.\n\n102.\n\nMorbid phenomena indicate in like manner the existence of organic\nand physical laws: for if a living being deviates from those rules\nwith reference to which it is constructed, it still seeks to agree\nwith the general vitality of nature in conformity with general laws,\nand throughout its whole course still proves the constancy of those\nprinciples on which the universe has existed, and by which it is held\ntogether.\n\n103.\n\nWe will here first advert to a very remarkable state in which the\nvision of many persons is found to be. As it presents a deviation\nfrom the ordinary mode of seeing colours, it might be fairly classed\nunder morbid impressions; but as it is consistent in itself, as it\noften occurs, may extend to several members of a family, and probably\ndoes not admit of cure, we may consider it as bordering only on the\nnosological cases, and therefore place it first.\n\n104.\n\nI was acquainted with two individuals not more than twenty years of\nage, who were thus affected: both had bluish-grey eyes, an acute sight\nfor near and distant objects, by day-light and candle-light, and their\nmode of seeing colours was in the main quite similar.\n\n105.\n\nThey agreed with the rest of the world in denominating white, black,\nand grey in the usual manner. Both saw white untinged with any hue. One\nsaw a somewhat brownish appearance in black, and in grey a somewhat\nreddish tinge. In general they appeared to have a very delicate\nperception of the gradations of light and dark.\n\n106.\n\nThey appeared to see yellow, red-yellow, and yellow-red,[1] like\nothers: in the last case they said they saw the yellow passing as it\nwere over the red as if glazed: some thickly-ground carmine, which had\ndried in a saucer, they called red.\n\n107.\n\nBut now a striking difference presented itself. If the carmine was\npassed thinly over the white saucer, they would compare the light\ncolour thus produced to the colour of the sky, and call it blue. If\na rose was shown them beside it, they would, in like manner, call it\nblue; and in all the trials which were made, it appeared that they\ncould not distinguish light blue from rose-colour. They confounded\nrose-colour, blue, and violet on all occasions: these colours only\nappeared to them to be distinguished from each other by delicate shades\nof lighter, darker, intenser, or fainter appearance.\n\n108.\n\nAgain they could not distinguish green from dark orange, nor, more\nespecially, from a red brown.\n\n109.\n\nIf any one, accidentally conversing with these individuals, happened\nto question them about surrounding objects, their answers occasioned\nthe greatest perplexity, and the interrogator began to fancy his own\nwits were out of order. With some method we may, however, approach to a\nnearer knowledge of the law of this deviation from the general law.\n\n110.\n\nThese persons, as may be gathered from what has been stated, saw fewer\ncolours than other people: hence arose the confusion of different\ncolours. They called the sky rose-colour, and the rose blue, or\n_vice versâ_. The question now is: did they see both blue or both\nrose-colour? did they see green orange, or orange green?\n\n111.\n\nThis singular enigma appears to solve itself, if we assume that they\nsaw no blue, but, instead of it, a light pure red, a rose-colour.\nWe can comprehend what would be the result of this by means of the\nchromatic diagram.\n\n112.\n\nIf we take away blue from the chromatic circle we shall miss violet and\ngreen as well. Pure red occupies the place of blue and violet, and in\nagain mixing with yellow the red produces orange where green should be.\n\n113.\n\nProfessing to be satisfied with this mode of explanation, we have named\nthis remarkable deviation from ordinary vision \"Acyanoblepsia.\"[2]\nWe have prepared some coloured figures for its further elucidation,\nand in explaining these we shall add some further details. Among the\nexamples will be found a landscape, coloured in the mode in which the\nindividuals alluded to appeared to see nature: the sky rose-colour, and\nall that should be green varying from yellow to brown red, nearly as\nfoliage appears to us in autumn[3].--Note H.\n\n114.\n\nWe now proceed to speak of morbid and other extraordinary affections\nof the retina, by which the eye may be susceptible of an appearance\nof light without external light, reserving for a future occasion the\nconsideration of galvanic light.\n\n115.\n\nIf the eye receives a blow, sparks seem to spread from it. In some\nstates of body, again, when the blood is heated, and the system much\nexcited, if the eye is pressed first gently, and then more and more\nstrongly, a dazzling and intolerable light may be excited.\n\n116.\n\nIf those who have been recently couched experience pain and heat in the\neye, they frequently see fiery flashes and sparks: these symptoms last\nsometimes for a week or fortnight, or till the pain and heat diminish.\n\n117.\n\nA person suffering from ear-ache saw sparks and balls of light in the\neye during each attack, as long as the pain lasted.\n\n118.\n\nPersons suffering from worms often experience extraordinary appearances\nin the eye, sometimes sparks of fire, sometimes spectres of light,\nsometimes frightful figures, which they cannot by an effort of the will\ncease to see: sometimes these appearances are double.\n\n119.\n\nHypochondriacs frequently see dark objects, such as threads, hairs,\nspiders, flies, wasps. These appearances also exhibit themselves in the\nincipient hard cataract. Many see semi-transparent small tubes, forms\nlike wings of insects, bubbles of water of various sizes, which fall\nslowly down, if the eye is raised: sometimes these congregate together\nso as to resemble the spawn of frogs; sometimes they appear as complete\nspheres, sometimes in the form of lenses.\n\n120.\n\nAs light appeared, in the former instances, without external light,\nso also these images appear without corresponding external objects.\nThe images are sometimes transient, sometimes they last during\nthe patient's life. Colour, again, frequently accompanies these\nimpressions: for hypochondriacs often see yellow-red stripes in the\neye: these are generally more vivid and numerous in the morning, or\nwhen lasting.\n\n121.\n\nWe have before seen that the impression of any object may remain for a\ntime in the eye: this we have found to be a physiological phenomenon\n(23): the excessive duration of such an impression, on the other band,\nmay be considered as morbid.\n\n122.\n\nThe weaker the organ the longer the impression of the image lasts.\nThe retina does not so soon recover itself; and the effect may be\nconsidered as a kind of paralysis (28).\n\n123.\n\nThis is not to be wondered at in the case of dazzling lights. If any\none looks at the sun, he may retain the image in his eyes for several\ndays. Boyle relates an instance of ten years.\n\n124.\n\nThe same takes place, in a certain degree, with regard to objects\nthat are not dazzling. Büsch relates of himself that the image of an\nengraving, complete in all its parts, was impressed on his eye for\nseventeen minutes.\n\n125.\n\nA person inclined to fulness of blood retained the image of a bright\nred calico, with white spots, many minutes in the eye, and saw it float\nbefore everything like a veil. It only disappeared by rubbing the eye\nfor some time.\n\n126.\n\nScherfer observes that the red colour, which is the consequence of a\npowerful impression of light, may last for some hours.\n\n127.\n\nAs we can produce an appearance of light on the retina by pressure\non the eyeball, so by a gentle pressure a red colour appears, thus\ncorresponding with the after-image of an impression of light.\n\n128.\n\nMany sick persons, on awaking, see everything in the colour of the\nmorning sky, as if through a red veil: so, if in the evening they doze\nand wake again, the same appearance presents itself. It remains for\nsome minutes, and always disappears if the eye is rubbed a little. Red\nstars and balls sometimes accompany the impression. This state may last\nfor a considerable time.\n\n129.\n\nThe aëronauts, particularly Zambeccari and his companions, relate\nthat they saw the moon blood-red at the highest elevation. As they\nhad ascended above the vapours of the earth, through which we see the\nmoon and sun naturally of such a colour, it may be suspected that this\nappearance may be classed with the pathological colours. The senses,\nnamely, may be so influenced by an unusual state, that the whole\nnervous system, and particularly the retina, may sink into a kind of\ninertness and inexcitability. Hence it is not impossible that the moon\nmight act as a very subdued light, and thus produce the impression of\nthe red colour. The sun even appeared blood-red to the aëronauts of\nHamburgh.\n\nIf those who are at some elevation in a balloon scarcely hear each\nother speak, may not this, too, be attributed to the inexcitable state\nof the nerves as well as to the thinness of the air?\n\n130.\n\nObjects are often seen by sick persons in variegated colours. Boyle\nrelates an instance of a lady, who, after a fall by which an eye was\nbruised, saw all objects, but especially white objects, glittering in\ncolours, even to an intolerable degree.\n\n131.\n\nPhysicians give the name of \"Chrupsia\" to an affection of the sight,\noccurring in typhoid maladies. In these cases the patients state that\nthey see the boundaries of objects coloured where light and dark meet.\nA change probably takes place in the humours of the eye, through which\ntheir achromatism is affected.\n\n132.\n\nIn cases of milky cataract, a very turbid crystalline lens causes\nthe patient to see a red light. In a case of this kind, which was\ntreated by the application of electricity, the red light changed by\ndegrees to yellow, and at last to white, when the patient again began\nto distinguish objects. These changes of themselves warranted the\nconclusion that the turbid state of the lens was gradually approaching\nthe transparent state. We shall be enabled easily to trace this effect\nto its source as soon as we become better acquainted with the physical\ncolours.\n\n133.\n\nIf again it may be assumed that a jaundiced patient sees through\nan actually yellow-coloured humour, we are at once referred to the\ndepartment of chemical colours, and it is thus evident that we can only\nthoroughly investigate the chapter of pathological colours when we\nhave made ourselves acquainted with the whole range of the remaining\nphenomena. What has been adduced may therefore suffice for the present,\ntill we resume the further consideration of this portion of our subject.\n\n134.\n\nIn conclusion we may, however, at once advert to some peculiar states\nor dispositions of the organ.\n\nThere are painters who, instead of rendering the colours of nature,\ndiffuse a general tone, a warm or cold hue, over the picture. In some,\nagain, a predilection for certain colours displays itself; in others a\nwant of feeling for harmony.\n\n135.\n\nLastly, it is also worthy of remark, that savage nations, uneducated\npeople, and children have a great predilection for vivid colours;\nthat animals are excited to rage by certain colours; that people of\nrefinement avoid vivid colours in their dress and the objects that are\nabout them, and seem inclined to banish them altogether from their\npresence.--Note I.\n\n\n[1] It has been found necessary to follow the author's nomenclature\nthroughout--T.\n\n[2] Non-perception of blue.\n\n[3] It has not been thought necessary to copy the plates here referred\nto.--T.\n\n\n\n\n## PART II.\n\n\n\n## PHYSICAL COLOURS.\n\n\n\n136.\n\nWe give this designation to colours which are produced by certain\nmaterial mediums: these mediums, however, have no colour themselves,\nand may be either transparent, semi-transparent yet transmitting light,\nor altogether opaque. The colours in question are thus produced in the\neye through such external given causes, or are merely reflected to\nthe eye when by whatever means they are already produced without us.\nAlthough we thus ascribe to them a certain objective character, their\ndistinctive quality still consists in their being transient, and not to\nbe arrested.\n\n137.\n\nThey are called by former investigators _colores apparentes, fluxi,\nfugitivi, phantastici, falsi, variantes_. They are also called\n_speciosi_ and _emphatici_, on account of their striking splendour.\nThey are immediately connected with the physiological colours, and\nappear to have but little more reality: for, while in the production\nof the physiological colours the eye itself was chiefly efficient, and\nwe could only perceive the phenomena thus evoked within ourselves,\nbut not without us, we have now to consider the fact that colours are\nproduced in the eye by means of colourless objects; that we thus too\nhave a colourless surface before us which is acted upon as the retina\nitself is, and that we can perceive the appearance produced upon it\nwithout us. In such a process, however, every observation will convince\nus that we have to do with colours in a progressive and mutable, but\nnot in a final or complete, state.\n\n138.\n\nHence, in directing our attention to these physical colours, we find\nit quite possible to place an objective phenomenon beside a subjective\none, and often by means of the union of the two successfully to\npenetrate farther into the nature of the appearance.\n\n139.\n\nThus, in the observations by which we become acquainted with the\nphysical colours, the eye is not to be considered as acting alone; nor\nis the light ever to be considered in immediate relation with the eye:\nbut we direct our attention especially to the various effects produced\nby mediums, those mediums being themselves colourless.\n\n140.\n\nLight under these circumstances may be affected by three conditions.\nFirst, when it flashes back from the surface of a medium; in\nconsidering which _catoptrical_ experiments invite our attention.\nSecondly, when it passes by the edge of a medium: the phenomena\nthus produced were formerly called _perioptical_; we prefer the\nterm _paroptical_. Thirdly, when it passes through either a merely\nlight-transmitting or an actually transparent body; thus constituting\na class of appearances on which _dioptrical_ experiments are founded.\nWe have called a fourth class of physical colours _epoptical_, as the\nphenomena exhibit themselves on the colourless surface of bodies under\nvarious conditions, without previous or actual dye (βαφή).--Note K.\n\n141.\n\nIn examining these categories with reference to our three leading\ndivisions, according to which we consider the phenomena of colours in a\nphysiological, physical, or chemical view, we find that the catoptrical\ncolours are closely connected with the physiological; the paroptical\nare already somewhat more distinct and independent; the dioptrical\nexhibit themselves as entirely and strictly physical, and as having\na decidedly objective character; the epoptical, although still only\napparent, may be considered as the transition to the chemical colours.\n\n142.\n\nIf we were desirous of prosecuting our investigation strictly in the\norder of nature, we ought to proceed according to the classification\nwhich has just been made; but in didactic treatises it is not of\nso much consequence to connect as to duly distinguish the various\ndivisions of a subject, in order that at last, when every single\nclass and case has been presented to the mind, the whole may be\nembraced in one comprehensive view. We therefore turn our attention\nforthwith to the dioptrical class, in order at once to give the reader\nthe full impression of the physical colours, and to exhibit their\ncharacteristics the more strikingly.\n\n\n\n\nIX.\n\n\n## DIOPTRICAL COLOURS.\n\n\n\n143.\n\nColours are called dioptrical when a colourless medium is necessary\nto produce them; the medium must be such that light and darkness can\nact through it either on the eye or on opposite surfaces. It is thus\nrequired that the medium should be transparent, or at least capable, to\na certain degree, of transmitting light.\n\n144.\n\nAccording to these conditions we divide the dioptrical phenomena into\ntwo classes, placing in the first those which are produced by means of\nimperfectly transparent, yet light-transmitting mediums; and in the\nsecond such as are exhibited when the medium is in the highest degree\ntransparent.\n\n\n\n\n## X — DIOPTRICAL COLOURS OF THE FIRST CLASS.\n\n\n\n145.\n\nSpace, if we assume it to be empty, would have the quality of absolute\ntransparency to our vision. If this space is filled so that the eye\ncannot perceive that it is so, there exists a more or less material\ntransparent medium, which may be of the nature of air and gas, may be\nfluid or even solid.\n\n146.\n\nThe pure and light-transmitting semi-transparent medium is only an\naccumulated form of the transparent medium. It may therefore be\npresented to us in three modes.\n\n147.\n\nThe extreme degree of this accumulation is white; the simplest,\nbrightest, first, opaque occupation of space.\n\n148.\n\nTransparency itself, empirically considered, is already the first\ndegree of the opposite state. The intermediate degrees from this point\nto opaque white are infinite.\n\n149.\n\nAt whatever point short of opacity we arrest the thickening medium, it\nexhibits simple and remarkable phenomena when placed in relation with\nlight and darkness.\n\n150.\n\nThe highest degree of light, such as that of the sun, of phosphorus\nburning in oxygen, is dazzling and colourless: so the light of the\nfixed stars is for the most part colourless. This light, however, seen\nthrough a medium but very slightly thickened, appears to us yellow.\nIf the density of such a medium be increased, or if its volume become\ngreater, we shall see the light gradually assume a yellow-red hue,\nwhich at last deepens to a ruby-colour.--Note L.\n\n151.\n\nIf on the other hand darkness is seen through a semi-transparent\nmedium, which is itself illumined by a light striking on it, a blue\ncolour appears: this becomes lighter and paler as the density of the\nmedium is increased, but on the contrary appears darker and deeper the\nmore transparent the medium becomes: in the least degree of dimness\nshort of absolute transparence, always supposing a perfectly colourless\nmedium, this deep blue approaches the most beautiful violet.\n\n152.\n\nIf this effect takes place in the eye as here described, and may\nthus be pronounced to be subjective, it remains further to convince\nourselves of this by objective phenomena. For a light thus mitigated\nand subdued illumines all objects in like manner with a yellow,\nyellow-red, or red hue; and, although the effect of darkness through\nthe non-transparent medium does not exhibit itself so powerfully, yet\nthe blue sky displays itself in the camera obscura very distinctly on\nwhite paper, as well as every other material colour.\n\n153.\n\nIn examining the cases in which this important leading phenomenon\nappears, we naturally mention the atmospheric colours first: most of\nthese may be here introduced in order.\n\n154.\n\nThe sun seen through a certain degree of vapour appears with a yellow\ndisk; the centre is often dazzlingly yellow when the edges are already\nred. The orb seen through a thick yellow mist appears ruby-red (as was\nthe case in 1794, even in the north); the same appearance is still\nmore decided, owing to the state of the atmosphere, when the scirocco\nprevails in southern climates: the clouds generally surrounding the sun\nin the latter case are of the same colour, which is reflected again on\nall objects.\n\nThe red hues of morning and evening are owing to the same cause. The\nsun is announced by a red light, in shining through a greater mass\nof vapours. The higher he rises, the yellower and brighter the light\nbecomes.\n\n155.\n\nIf the darkness of infinite space is seen through atmospheric vapours\nillumined by the day-light, the blue colour appears. On high mountains\nthe sky appears by day intensely blue, owing to the few thin vapours\nthat float before the endless dark space: as soon as we descend in the\nvalleys, the blue becomes lighter; till at last, in certain regions,\nand in consequence of increasing vapours, it altogether changes to a\nvery pale blue.\n\n156.\n\nThe mountains, in like manner, appear to us blue; for, as we see them\nat so great a distance that we no longer distinguish the local tints,\nand as no light reflected from their surface acts on our vision, they\nare equivalent to mere dark objects, which, owing to the interposed\nvapours, appear blue.\n\n157.\n\nSo we find the shadowed parts of nearer objects are blue when the air\nis charged with thin vapours.\n\n158.\n\nThe snow-mountains, on the other hand, at a great distance, still\nappear white, or approaching to a yellowish hue, because they act on\nour eyes as brightness seen through atmospheric vapour.\n\n159.\n\nThe blue appearance at the lower part of the flame of a candle belongs\nto the same class of phenomena. If the flame be held before a white\nground, no blue will be seen, but this colour will immediately appear\nif the flame is opposed to a black ground. This phenomenon may be\nexhibited most strikingly with a spoonful of lighted spirits of wine.\nWe may thus consider the lower part of the flame as equivalent to the\nvapour which, although infinitely thin, is still apparent before the\ndark surface; it is so thin, that one may easily see to read through\nit: on the other hand, the point of the flame which conceals objects\nfrom our sight is to be considered as a self-illuminating body.\n\n160.\n\nLastly, smoke is also to be considered as a semi-transparent medium,\nwhich appears to us yellow or reddish before a light ground, but blue\nbefore a dark one.\n\n161.\n\nIf we now turn our attention to fluid mediums, we find that water,\ndeprived in a very slight degree of its transparency, produces the same\neffects.\n\n162.\n\nThe infusion of the lignum nephriticum (guilandina Linnæi), which\nformerly excited so much attention, is only a semi-transparent liquor,\nwhich in dark wooden cups must appear blue, but held towards the sun in\na transparent glass must exhibit a yellow appearance.\n\n163.\n\nA drop of scented water, of spirit varnish, of several metallic\nsolutions, may be employed to give various degrees of opacity to water\nfor such experiments. Spirit of soap perhaps answers best.\n\n164.\n\nThe bottom of the sea appears to divers of a red colour in bright\nsunshine: in this case the water, owing to its depth, acts as a\nsemi-transparent medium. Under these circumstances, they find the\nshadows green, which is the complemental colour.\n\n165.\n\nAmong solid mediums the opal attracts our attention first: its colours\nare, at least, partly to be explained by the circumstance that it is,\nin fact, a semi-transparent medium, through which sometimes light,\nsometimes dark, substrata are visible.\n\n166.\n\nFor these experiments, however, the opal-glass (vitrum astroides,\ngirasole) is the most desirable material. It is prepared in various\nways, and its semi-opacity is produced by metallic oxydes. The same\neffect is produced also by melting pulverised and calcined bones\ntogether with the glass, on which account it is also known by the name\nof _beinglas_; but, prepared in this mode, it easily becomes too opaque.\n\n167.\n\nThis glass may be adapted for experiments in various ways: it may\neither be made in a very slight degree non-transparent, in which case\nthe light seen through various layers placed one upon the other may\nbe deepened from the lightest yellow to the deepest red, or, if made\noriginally more opaque, it may be employed in thinner or thicker\nlaminæ. The experiments may be successfully made in both ways: in\norder, however, to see the bright blue colour, the glass should neither\nbe too opaque nor too thick. For, as it is quite natural that darkness\nmust act weakly through the semi-transparent medium, so this medium, if\ntoo thick, soon approaches whiteness.\n\n168.\n\nPanes of glass throw a yellow light on objects through those parts\nwhere they happen to be semi-opaque, and these same parts appear blue\nif we look at a dark object through them.\n\n169.\n\nSmoked glass may be also mentioned here, and is, in like manner, to be\nconsidered as a semi-opaque medium. It exhibits the sun more or less\nruby-coloured; and, although this appearance may be attributed to the\nblack-brown colour of the soot, we may still convince ourselves that a\nsemi-transparent medium here acts if we hold such a glass moderately\nsmoked, and lit by the sun on the unsmoked side, before a dark object,\nfor we shall then perceive a bluish appearance.\n\n170.\n\nA striking experiment may be made in a dark room with sheets of\nparchment. If we fasten a piece of parchment before the opening in the\nwindow-shutter when the sun shines, it will appear nearly white; by\nadding a second, a yellowish colour appears, which still increases as\nmore leaves are added, till at last it changes to red.\n\n171.\n\nA similar effect, owing to the state of the crystalline lens in milky\ncataract, has been already adverted to (131).\n\n172.\n\nHaving now, in tracing these phenomena, arrived at the effect of a\ndegree of opacity scarcely capable of transmitting light, we may here\nmention a singular appearance which was owing to a momentary state of\nthis kind.\n\nA portrait of a celebrated theologian had been painted some years\nbefore the circumstance to which we allude, by an artist who was known\nto have considerable skill in the management of his materials. The\nvery reverend individual was represented in a rich velvet dress, which\nwas not a little admired, and which attracted the eye of the spectator\nalmost more than the face. The picture, however, from the effect of the\nsmoke of lamps and dust, had lost much of its original vivacity. It\nwas, therefore, placed in the hands of a painter, who was to clean it,\nand give it a fresh coat of varnish. This person began his operations\nby carefully washing the picture with a sponge: no sooner, however,\nhad he gone over the surface once or twice, and wiped away the first\ndirt, than to his amazement the black velvet dress changed suddenly to\na light blue plush, which gave the ecclesiastic a very secular, though\nsomewhat old-fashioned, appearance. The painter did not venture to go\non with his washing: he could not comprehend how a light blue should be\nthe ground of the deepest black, still less how he could so suddenly\nhave removed a glazing colour capable of converting the one tint to the\nother.\n\nAt all events, he was not a little disconcerted at having spoilt the\npicture to such an extent. Nothing to characterize the ecclesiastic\nremained but the richly-curled round wig, which made the exchange\nof a faded plush for a handsome new velvet dress far from desirable.\nMeanwhile, the mischief appeared irreparable, and the good artist,\nhaving turned the picture to the wall, retired to rest with a mind ill\nat ease. But what was his joy the next morning, when, on examining the\npicture, he beheld the black velvet dress again in its full splendour.\nHe could not refrain from again wetting a corner, upon which the blue\ncolour again appeared, and after a time vanished. On hearing of this\nphenomenon, I went at once to see the miraculous picture. A wet sponge\nwas passed over it in my presence, and the change quickly took place. I\nsaw a somewhat faded, but decidedly light blue plush dress, the folds\nunder the arm being indicated by some brown strokes.\n\nI explained this appearance to myself by the doctrine of the\nsemi-opaque medium. The painter, in order to give additional depth\nto his black, may have passed some particular varnish over it: on\nbeing washed, this varnish imbibed some moisture, and hence became\nsemi-opaque, in consequence of which the black underneath immediately\nappeared blue. Perhaps those who are practically acquainted with the\neffect of varnishes may, through accident or contrivance, arrive at\nsome means of exhibiting this singular appearance, as an experiment, to\nthose who are fond of investigating natural phenomena. Notwithstanding\nmany attempts, I could not myself succeed in re-producing it.\n\n173.\n\nHaving now traced the most splendid instances of atmospheric\nappearances, as well as other less striking yet sufficiently remarkable\ncases, to the leading examples of semi-transparent mediums, we have no\ndoubt that attentive observers of nature will carry such researches\nfurther, and accustom themselves to trace and explain the various\nappearances which present themselves in every-day experience on the\nsame principle: we may also hope that such investigators will provide\nthemselves with an adequate apparatus in order to place remarkable\nfacts before the eyes of others who may be desirous of information.\n\n174.\n\nWe venture, once for all, to call the leading appearance in question,\nas generally described in the foregoing pages, a primordial and\nelementary phenomenon; and we may here be permitted at once to state\nwhat we understand by the term.\n\n175.\n\nThe circumstances which come under our notice in ordinary observation\nare, for the most part, insulated cases, which, with some attention,\nadmit of being classed under general leading facts. These again range\nthemselves under theoretical rubrics which are more comprehensive, and\nthrough which we become better acquainted with certain indispensable\nconditions of appearances in detail. From henceforth everything is\ngradually arranged under higher rules and laws, which, however, are not\nto be made intelligible by words and hypotheses to the understanding\nmerely, but, at the same time, by real phenomena to the senses. We\ncall these primordial phenomena, because nothing appreciable by the\nsenses lies beyond them, on the contrary, they are perfectly fit to be\nconsidered as a fixed point to which we first ascended, step by step,\nand from which we may, in like manner, descend to the commonest case\nof every-day experience. Such an original phenomenon is that which has\nlately engaged our attention. We see on the one side light, brightness;\non the other darkness, obscurity: we bring the semi-transparent medium\nbetween the two, and from these contrasts and this medium the colours\ndevelop themselves, contrasted, in like manner, but soon, through a\nreciprocal relation, directly tending again to a point of union.[1]\n\n176.\n\nWith this conviction we look upon the mistake that has been committed\nin the investigation of this subject to be a very serious one, inasmuch\nas a secondary phenomenon has been thus placed higher in order--the\nprimordial phenomenon has been degraded to an inferior place; nay, the\nsecondary phenomenon has been placed at the head, a compound effect has\nbeen treated as simple, a simple appearance as compound: owing to this\ncontradiction, the most capricious complication and perplexity have\nbeen introduced into physical inquiries, the effects of which are still\napparent.\n\n177.\n\nBut when even such a primordial phenomenon is arrived at, the evil\nstill is that we refuse to recognise it as such, that we still aim at\nsomething beyond, although it would become us to confess that we are\narrived at the limits of experimental knowledge. Let the observer of\nnature suffer the primordial phenomenon to remain undisturbed in its\nbeauty; let the philosopher admit it into his department, and he will\nfind that important elementary facts are a worthier basis for further\noperations than insulated cases, opinions, and hypotheses.--Note M.\n\n\n[1] That is (according to the author's statement 150. 151.) both tend\nto red; the yellow deepening to orange as the comparatively dark medium\nis thickened before brightness; the blue deepening to violet as the\nlight medium is thinned before darkness.--T.\n\n\n\n\n[Pg 74]\n\n\n\n## XI — DIOPTRICAL COLOURS OF THE SECOND CLASS.--REFRACTION.\n\n\n\n178.\n\nDioptrical colours of both classes are closely connected, as will\npresently appear on a little examination. Those of the first class\nappeared through semi-transparent mediums, those of the second class\nwill now appear through transparent mediums. But since every substance,\nhowever transparent, may be already considered to partake of the\nopposite quality (as every accumulation of a medium called transparent\nproves), so the near affinity of the two classes is sufficiently\nmanifest.\n\n179.\n\nWe will, however, first consider transparent mediums abstractedly as\nsuch, as entirely free from any degree of opacity, and direct our whole\nattention to a phenomenon which here presents itself, and which is\nknown by the name of refraction.\n\n180.\n\nIn treating of the physiological colours, we have already had occasion\nto vindicate what [Pg 75] were formerly called illusions of sight, as\nthe active energies of the healthy and duly efficient eye (2), and we\nare now again invited to consider similar instances confirming the\nconstancy of the laws of vision.\n\n181.\n\nThroughout nature, as presented to the senses, everything depends on\nthe relation which things bear to each other, but especially on the\nrelation which man, the most important of these, bears to the rest.\nHence the world divides itself into two parts, and the human being\nas _subject_, stands opposed to the _object_. Thus the practical\nman exhausts himself in the accumulation of facts, the thinker in\nspeculation; each being called upon to sustain a conflict which admits\nof no peace and no decision.\n\n182.\n\nBut still the main point always is, whether the relations are truly\nseen. As our senses, if healthy, are the surest witnesses of external\nrelations, so we may be convinced that, in all instances where they\nappear to contradict reality, they lay the greater and surer stress\non true relations. Thus a distant object appears to us smaller; and\nprecisely by this means we are aware of distance. We produced coloured\nappearances on colourless objects, through colourless mediums, and at\nthe same moment our attention was called to the degree of opacity in\nthe medium.\n\n183.\n\nThus the different degrees of opacity in so-called transparent mediums,\nnay, even other physical and chemical properties belonging to them,\nare known to our vision by means of refraction, and invite us to make\nfurther trials in order to penetrate more completely by physical and\nchemical means into those secrets which are already opened to our view\non one side.\n\n184.\n\nObjects seen through mediums more or less transparent do not appear\nto us in the place which they should occupy according to the laws of\nperspective. On this fact the dioptrical colours of the second class\ndepend.\n\n185.\n\nThose laws of vision which admit of being expressed in mathematical\nformulæ are based on the principle that, as light proceeds in straight\nlines, it must be possible to draw a straight line from the eye to any\ngiven object in order that it be seen. If, therefore, a case arises in\nwhich the light arrives to us in a bent or broken line, that we see the\nobject by means of a bent or broken line, we are at once informed that\nthe medium between the eye and the object is denser, or that it has\nassumed this or that foreign nature.\n\n186.\n\nThis deviation from the law of right-lined vision is known by the\ngeneral term of refraction; and, although we may take it for granted\nthat our readers are sufficiently acquainted with its effects, yet we\nwill here once more briefly exhibit it in its objective and subjective\npoint of view.\n\n187.\n\nLet the sun shine diagonally into an empty cubical vessel, so that\nthe opposite side be illumined, but not the bottom: let water be\nthen poured into this vessel, and the direction of the light will\nbe immediately altered; for a part of the bottom is shone upon. At\nthe point where the light enters the thicker medium it deviates from\nits rectilinear direction, and appears broken: hence the phenomenon\nis called the breaking (_brechung_) or refraction. Thus much of the\nobjective experiment.\n\n188.\n\nWe arrive at the subjective fact in the following mode:--Let the eye\nbe substituted for the sun: let the sight be directed in like manner\n[Pg 78] diagonally over one side, so that the opposite inner side be\nentirely seen, while no part of the bottom is visible. On pouring in\nwater the eye will perceive a part of the bottom; and this takes place\nwithout our being aware that we do not see in a straight line; for\nthe bottom appears to us raised, and hence we give the term elevation\n(_hebung_) to the subjective phenomenon. Some points, which are\nparticularly remarkable with reference to this, will be adverted to\nhereafter.\n\n189.\n\nWere we now to express this phenomenon generally, we might here repeat,\nin conformity with the view lately taken, that the relation of the\nobjects is changed or deranged.\n\n190.\n\nBut as it is our intention at present to separate the objective from\nthe subjective appearances, we first express the phenomenon in a\nsubjective form, and say,--a derangement or displacement of the object\nseen, or to be seen, takes place.\n\n191.\n\nBut that which is seen without a limiting outline may be thus affected\nwithout our perceiving the change. On the other hand, if what we look\nat has a visible termination, we have an evident indication that a\ndisplacement occurs. If, therefore, [Pg 79] we wish to ascertain the\nrelation or degree of such a displacement, we must chiefly confine\nourselves to the alteration of surfaces with visible boundaries; in\nother words, to the displacement of circumscribed objects.\n\n192.\n\nThe general effect may take place through parallel mediums, for every\nparallel medium displaces the object by bringing it perpendicularly\ntowards the eye. The apparent change of position is, however, more\nobservable through mediums that are not parallel.\n\n193.\n\nThese latter may be perfectly spherical, or may be employed in the\nform of convex or concave lenses. We shall make use of all these as\noccasion may require in our experiments. But as they not only displace\nthe object from its position, but alter it in various ways, we shall,\nin most cases, prefer employing mediums with surfaces, not, indeed,\nparallel with reference to each other, but still altogether plane,\nnamely, prisms. These have a triangle for their base, and may, it is\ntrue, be considered as portions of a lens, but they are particularly\navailable for our experiments, inasmuch as they very perceptibly\ndisplace the object from its position, without producing a remarkable\ndistortion.\n\n194.\n\nAnd now, in order to conduct our observations with as much exactness\nas possible, and to avoid all confusion and ambiguity, we confine\nourselves at first to\n\n\n## SUBJECTIVE EXPERIMENTS,\n\n\n\nin which, namely, the object is seen by the observer through a\nrefracting medium. As soon as we have treated these in due series, the\nobjective experiments will follow in similar order.\n\n\n\n\nXII.\n\n\n## REFRACTION WITHOUT THE APPEARANCE OF COLOUR.\n\n\n\n195.\n\nRefraction can visibly take place without our perceiving an appearance\nof colour. To whatever extent a colourless or uniformly coloured\nsurface may be altered as to its position by refraction, no colour\nconsequent upon refraction appears within it, provided it has no\noutline or boundary. We may convince ourselves of this in various ways.\n\n196.\n\nPlace a glass cube on any larger surface, and look through the glass\nperpendicularly or obliquely, the unbroken surface opposite the eye\nappears altogether raised, but no colour exhibits itself. If we look at\na pure grey or blue sky or a uniformly white or coloured wall through a\nprism, the portion of the surface which the eye thus embraces will be\naltogether changed as to its position, without our therefore observing\nthe smallest appearance of colour.\n\n\n\n\n## XIII.\n\n\n\n## CONDITIONS OF THE APPEARANCE OF COLOUR.\n\n\n\n197.\n\nAlthough in the foregoing experiments we have found all unbroken\nsurfaces, large or small, colourless, yet at the outlines or\nboundaries, where the surface is relieved upon a darker or lighter\nobject, we observe a coloured appearance.\n\n198.\n\nOutline, as well as surface, is necessary to constitute a figure or\ncircumscribed object. We therefore express the leading fact thus:\ncircumscribed objects must be displaced by refraction in order to the\nexhibition of an appearance of colour.\n\n199.\n\nWe place before us the simplest object, a light disk on a dark ground\n(A).[1] A displacement occurs with regard to this object, if we\napparently extend its outline from the centre by magnifying it. This\nmay be done with any convex glass, and in this case we see a blue edge\n(B).\n\n200.\n\nWe can, to appearance, contract the circumference of the same light\ndisk towards the centre by diminishing the object; the edge will then\nappear yellow (C). This may be done with a concave glass, which,\nhowever, should not be ground thin like common eye-glasses, but must\nhave some substance. In order, however, to make this experiment at once\nwith the convex glass, let a smaller black disk be inserted within\nthe light disk on a black ground. If we magnify the black disk on a\nwhite ground with a convex glass, the same result takes place as if we\ndiminished the white disk; for we extend the black outline upon the\nwhite, and we thus perceive the yellow edge together with the blue edge\n(D).\n\n201.\n\nThese two appearances, the blue and yellow, exhibit themselves in and\nupon the white: they both assume a reddish hue, in proportion as they\nmingle with the black.[2]\n\n[Illustration]\n\n202.\n\nIn this short statement we have described the primordial phenomena of\nall appearance of colour occasioned by refraction. These undoubtedly\nmay be repeated, varied, and rendered more striking; may be combined,\ncomplicated, confused; but, after all, may be still restored to their\noriginal simplicity.\n\n203.\n\nIn examining the process of the experiment just given, we find that\nin the one case we have, to appearance, extended the white edge upon\nthe dark surface; in the other we have extended the dark edge upon\nthe white surface, supplanting one by the other, pushing one over\nthe other. We will now endeavour, step by step, to analyse these and\nsimilar cases.\n\n204.\n\nIf we cause the white disk to move, in appearance, entirely from its\nplace, which can be done effectually by prisms, it will be coloured\naccording to the direction in which it apparently moves, in conformity\nwith the above laws. If we look at the disk _a_[3] through a prism,\nso that it appear moved to _b_, the outer edge will appear blue and\nblue-red, according to the law of the figure B (fig. 1), the other\nedge being yellow, and yellow-red, according to the law of the figure\nC (fig. 1). For in the first case the white figure is, as it were,\nextended over the dark boundary, and in the other case the dark\nboundary is passed over the white figure. The same happens if the disk\nis, to appearance, moved from _a_ to _c_, from _a_ to _d_, and so\nthroughout the circle.\n\n205.\n\nAs it is with the simple effect, so it is with more complicated\nappearances. If we look through a horizontal prism (_a b_[4]) at a\nwhite disk placed at some distance behind it at _e_, the disk will\nbe raised to _f_, and coloured according to the above law. If we\nremove this prism, and look through a vertical one (_c d_) at the same\ndisk, it will appear at _h_, and coloured according to the same law.\nIf we place the two prisms one upon the other, the disk will appear\ndisplaced diagonally, in conformity with a general law of nature, and\nwill be coloured as before; that is, according to its movement in the\ndirection, _e.g._:[5]\n\n206.\n\nIf we attentively examine these opposite coloured edges, we find that\nthey only appear in the direction of the apparent change of place.\nA round figure leaves us in some degree uncertain as to this: a\nquadrangular figure removes all doubt.\n\n207.\n\nThe quadrangular figure _a_,[6] moved in the direction _a b_ or _a d_\nexhibits no colour on the sides which are parallel with the direction\nin which it moves: on the other hand, if moved in the direction _a\nc_, parallel with its diagonal, all the edges of the figure appear\ncoloured.[7]\n\n208.\n\nThus, a former position (203) is here confirmed; viz. to produce\ncolour, an object must be so displaced that the light edges be\napparently carried over a dark surface, the dark edges over a light\nsurface, the figure over its boundary, the boundary over the figure.\nBut if the rectilinear boundaries of a figure could be indefinitely\nextended by refraction, so that figure and background might only pursue\ntheir course next, but not over each other, no colour would appear, not\neven if they were prolonged to infinity.\n\n\n[1] Plate 2, fig. 1.\n\n[2] The author has omitted the orange and purple in the coloured\ndiagrams which illustrate these first experiments, from a wish probably\nto present the elementary contrast, on which he lays a stress, in\ngreater simplicity. The reddish tinge would be apparent, as stated\nabove, where the blue and yellow are in contact with the black.--T.\n\n[3] Plate 2, fig. 2\n\n[4] Plate 2, fig. 4\n\n[5] In this case, according to the author, the refracting medium being\nincreased in mass, the appearance of colour is increased, and the\ndisplacement is greater.--T.\n\n[6] Plate 2, fig. 3.\n\n[7] Fig. 2, plate 1, contains a variety of forms, which, when viewed\nthrough a prism, are intended to illustrate the statement in this and\nthe following paragraph.\n\n\n\n\nXIV.\n\n\n## CONDITIONS UNDER WHICH THE APPEARANCE OF COLOUR INCREASES.\n\n\n\n209.\n\nWe have seen in the foregoing experiments that all appearance of colour\noccasioned by refraction depends on the condition that the boundary or\nedge be moved in upon the object itself, or the object itself over the\nground, that the figure should be, as it were, carried over itself, or\nover the ground. And we shall now find that, by increased displacement\nof the object, the appearance of colour exhibits itself in a greater\ndegree. This takes place in subjective experiments, to which, for the\npresent, we confine ourselves, under the following conditions.\n\n210.\n\nFirst, if, in looking through parallel mediums, the eye is directed\nmore obliquely.\n\nSecondly, if the surfaces of the medium are no longer parallel, but\nform a more or less acute angle.\n\nThirdly, owing to the increased proportion of the medium, whether\nparallel mediums be increased in size, or whether the angle be\nincreased, provided it does not attain a right angle.\n\nFourthly, owing to the distance of the eye armed with a refracting\nmedium from the object to be displaced.\n\nFifthly, owing to a chemical property that may be communicated to the\nglass, and which may be afterwards increased in effect.\n\n211.\n\nThe greatest change of place, short of considerable distortion of the\nobject, is produced by means of prisms, and this is the reason why the\nappearance of colour can be exhibited most powerfully through glasses\nof this form. Yet we will not, in employing them, suffer ourselves to\nbe dazzled by the splendid appearances they exhibit, but keep the above\nwell-established, simple principles calmly in view.\n\n212.\n\nThe colour which is outside, or foremost, in the apparent change of an\nobject by refraction, is always the broader, and we will henceforth\ncall this a _border_: the colour that remains next the outline is the\nnarrower, and this we will call an _edge_.\n\n213.\n\nIf we move a dark boundary towards a light surface, the yellow broader\nborder is foremost, and the narrower yellow-red edge follows close to\nthe outline. If we move a light boundary towards a dark surface, the\nbroader violet border is foremost, and the narrower blue edge follows.\n\n214.\n\nIf the object is large, its centre remains uncoloured. Its inner\nsurface is then to be considered as unlimited (195): it is displaced,\nbut not otherwise altered: but if the object is so narrow, that under\nthe above conditions the yellow border can reach the blue edge, the\nspace between the outlines will be entirely covered with colour. If we\nmake this experiment with a white stripe on a black ground,[1] the two\nextremes will presently meet, and thus produce green. We shall then see\nthe following series of colours:--\n\n    Yellow-red.\n    Yellow.\n    Green.\n    Blue.\n    Blue-red.\n\n215.\n\nIf we place a black band, or stripe, on white paper,[2] the violet\nborder will spread till it meets the yellow-red edge. In this case the\nintermediate black is effaced (as the intermediate white was in the\nlast experiment), and in its stead a splendid pure red will appear.[3]\nThe series of colours will now be as follows:--\n\n    Blue.\n    Blue-red.\n    Red.\n    Yellow-red.\n    Yellow.\n\n216.\n\nThe yellow and blue, in the first case (214), can by degrees meet so\nfully, that the two colours blend entirely in green, and the order will\nthen be,\n\n    Yellow-red.\n    Green.\n    Blue-red.\n\nIn the second case (215), under similar circumstances, we see only\n\n    Blue.\n    Red.\n    Yellow.\n\nThis appearance is best exhibited by refracting the bars of a window\nwhen they are relieved on a grey sky.[4]\n\n217.\n\nIn all this we are never to forget that this appearance is not to be\nconsidered as a complete or final state, but always as a progressive,\nincreasing, and, in many senses, controllable appearance. Thus we\nfind that, by the negation of the above five conditions, it gradually\ndecreases, and at last disappears altogether.\n\n\n[1] Plate 2, fig. 5, _left_.\n\n[2] Plate 2, fig. 5, _right_.\n\n[3] This pure red, the union of orange and violet, is considered by the\nauthor the maximum of the coloured appearance: he has appropriated the\nterm _purpur_ to it. See paragraph 703, and _note_.--T.\n\n[4] The bands or stripes in fig. 4, plate 1, when viewed through a\nprism, exhibit the colours represented in plate 2, fig. 5.\n\n\n\n\nXV.\n\n\n## EXPLANATION OF THE FOREGOING PHENOMENA.\n\n\n\n218.\n\nBefore we proceed further, it is incumbent on us to explain the first\ntolerably simple phenomenon, and to show its connexion with the\nprinciples first laid down, in order that the observer of nature may\nbe enabled clearly to comprehend the more complicated appearances that\nfollow.\n\n219.\n\nIn the first place, it is necessary to remember that we have to do\nwith circumscribed objects. In the act of seeing, generally, it is\nthe circumscribed visible which chiefly invites our observation; and\nin the present instance, in speaking of the appearance of colour, as\noccasioned by refraction, the circumscribed visible, the detached\nobject solely occupies our attention.\n\n220.\n\nFor our chromatic exhibitions we can, however, divide objects generally\ninto _primary_ and _secondary_. The expressions of themselves denote\nwhat we understand by them, but our meaning will be rendered still more\nplain by what follows.\n\n221.\n\nPrimary objects may be considered firstly as _original_, as images\nwhich are impressed on the eye by things before it, and which assure\nus of their reality. To these the secondary images may be opposed\nas _derived_ images, which remain in the organ when the object\nitself is taken away; those apparent after-images, which have been\ncircumstantially treated of in the doctrine of physiological colours.\n\n222.\n\nThe primary images, again, may be considered as _direct_ images, which,\nlike the original impressions, are conveyed immediately from the object\nto the eye. In contradistinction to these, the secondary images may\nbe considered as _indirect_, being only conveyed to us, as it were,\nat second-hand from a reflecting surface. These are the mirrored, or\ncatoptrical, images, which in certain cases can also become double\nimages:\n\n223.\n\nWhen, namely, the reflecting body is transparent, and has two parallel\nsurfaces, one behind the other: in such a case, an image may be\nreflected to the eye from both surfaces, and thus arise double images,\ninasmuch as the upper image does not quite cover the under one: this\nmay take place in various ways.\n\nLet a playing-card be held before a mirror. We shall at first see the\ndistinct image of the card, but the edge of the whole card, as well\nas that of every spot upon it, will be bounded on one side with a\nborder, which is the beginning of the second reflection. This effect\nvaries in different mirrors, according to the different thickness of\nthe glass, and the accidents of polishing. If a person wearing a white\nwaistcoat, with the remaining part of his dress dark, stands before\ncertain mirrors, the border appears very distinctly, and in like manner\nthe metal buttons on dark cloth exhibit the double reflection very\nevidently.\n\n224.\n\nThe reader who has made himself acquainted with our former descriptions\nof experiments (80) will the more readily follow the present statement.\nThe window-bars reflected by plates of glass appear double, and\nby increased thickness of the glass, and a due adaptation of the\nangle of reflection, the two reflections may be entirely separated\nfrom each other. So a vase full of water, with a plane mirror-like\nbottom, reflects any object twice, the two reflections being more or\nless separated under the same conditions. In these cases it is to be\nobserved that, where the two reflections cover each other, the perfect\nvivid image is reflected, but where they are separated they exhibit\nonly weak, transparent, and shadowy images.\n\n225.\n\nIf we wish to know which is the under and which the upper image, we\nhave only to take a coloured medium, for then a light object reflected\nfrom the under surface is of the colour of the medium, while that\nreflected from the upper surface presents the complemental colour. With\ndark objects it is the reverse; hence black and white surfaces may be\nhere also conveniently employed. How easily the double images assume\nand evoke colours will here again be striking.\n\n226.\n\nThirdly, the primary images may be considered as _principal_ images,\nwhile the secondary can be, as it were, annexed to these as _accessory_\nimages. Such an accessory image produces a sort of double form; except\nthat it does not separate itself from the principal object, although it\nmay be said to be always endeavouring to do so. It is with secondary\nimages of this last description that we have to do in prismatic\nappearances.\n\n227.\n\nA surface without a boundary exhibits no appearance of colour when\nrefracted (195). Whatever is seen must be circumscribed by an\noutline to produce this effect. In other words a figure, an object,\nis required; this object undergoes an apparent change of place by\nrefraction: the change is however not complete, not clean, not sharp;\nbut incomplete, inasmuch as an accessory image only is produced.\n\n228.\n\nIn examining every appearance of nature, but especially in examining\nan important and striking one, we should not remain in one spot, we\nshould not confine ourselves to the insulated fact, nor dwell on it\nexclusively, but look round through all nature to see where something\nsimilar, something that has affinity to it, appears: for it is only by\ncombining analogies that we gradually arrive at a whole which speaks\nfor itself, and requires no further explanation.\n\n229.\n\nThus we here call to mind that in certain cases refraction\nunquestionably produces double images, as is the case in Iceland spar:\nsimilar double images are also apparent in cases of refraction through\nlarge rock crystals, and in other instances; phenomena which have not\nhitherto been sufficiently observed.[1]\n\n230.\n\nBut since in the case under consideration (227) the question relates\nnot to double but to accessory images, we refer to a phenomenon already\nadverted to, but not yet thoroughly investigated. We allude to an\nearlier experiment, in which it appeared that a sort of conflict took\nplace in regard to the retina between a light object and its dark\nground, and between a dark object and its light ground (16). The light\nobject in this case appeared larger, the dark one smaller.\n\n231.\n\nBy a more exact observation of this phenomenon we may remark that the\nforms are not sharply distinguished from the ground, but that they\nappear with a kind of grey, in some degree, coloured edge; in short,\nwith an accessory image. If, then, objects seen only with the naked\neye produce such effects, what may not take place when a dense medium\nis interposed? It is not that alone which presents itself to us in\nobvious operation which produces and suffers effects, but likewise all\nprinciples that have a mutual relation only of some sort are efficient\naccordingly, and indeed often in a very high degree.\n\n232.\n\nThus when refraction produces its effect on an object there appears an\naccessory image next the object itself: the real form thus refracted\nseems even to linger behind, as if resisting the change of place; but\nthe accessory image seems to advance, and extends itself more or less\nin the mode already shown (212-216).\n\n233.\n\nWe also remarked (224) that in double images the fainter appear only\nhalf substantial, having a kind of transparent, evanescent character,\njust as the fainter shades of double shadows must always appear as\nhalf-shadows. These latter assume colours easily, and produce them\nreadily (69), the former also (80); and the same takes place in the\ninstance of accessory images, which, it is true, do not altogether\nquit the real object, but still advance or extend from it as\nhalf-substantial images, and hence can appear coloured so quickly and\nso powerfully.\n\n234.\n\nThat the prismatic appearance is in fact an accessory image we may\nconvince ourselves in more than one mode. It corresponds exactly with\nthe form of the object itself. Whether the object be bounded by a\nstraight line or a curve, indented or waving, the form of the accessory\nimage corresponds throughout exactly with the form of the object.[2]\n\n235.\n\nAgain, not only the form but other qualities of the object are\ncommunicated to the accessory image. If the object is sharply relieved\nfrom its ground, like white on black, the coloured accessory image in\nlike manner appears in its greatest force. It is vivid, distinct, and\npowerful; but it is most especially powerful when a luminous object is\nshown on a dark ground, which may be contrived in various ways.\n\n236.\n\nBut if the object is but faintly distinguished from the ground, like\ngrey objects on black or white, or even on each other, the accessory\nimage is also faint, and, when the original difference of tint or force\nis slight, becomes hardly discernible.\n\n237.\n\nThe appearances which are observable when coloured objects are relieved\non light, dark, or coloured grounds are, moreover, well worthy of\nattention. In this case a union takes place between the apparent colour\nof the accessory image and the real colour of the object; a compound\ncolour is the result, which is either assisted and enhanced by the\naccordance, or neutralised by the opposition of its ingredients.\n\n238.\n\nBut the common and general characteristic both of the double and\naccessory image is semi-transparence. The tendency of a transparent\nmedium to become only half transparent, or merely light-transmitting,\nhas been before adverted to (147, 148). Let the reader assume that he\nsees within or through such a medium a visionary image, and he will at\nonce pronounce this latter to be a semi-transparent image.\n\n239.\n\nThus the colours produced by refraction may be fitly explained by the\ndoctrine of the semi-transparent mediums. For where dark passes over\nlight, as the border of the semi-transparent accessory image advances,\nyellow appears; and, on the other hand, where a light outline passes\nover the dark background, blue appears (150, 151).\n\n240.\n\nThe advancing foremost colour is always the broader. Thus the yellow\nspreads over the light with a broad border, but the yellow-red appears\nas a narrower stripe and is next the dark, according to the doctrine of\naugmentation, as an effect of shade.[3]\n\n241.\n\nOn the opposite side the condensed blue is next the edge, while the\nadvancing border, spreading as a thinner veil over the black, produces\nthe violet colour, precisely on the principles before explained in\ntreating of semi-transparent mediums, principles which will hereafter\nbe found equally efficient in many other cases.\n\n242.\n\nSince an analysis like the present requires to be confirmed by ocular\ndemonstration, we beg every reader to make himself acquainted with the\nexperiments hitherto adduced, not in a superficial manner, but fairly\nand thoroughly. We have not placed arbitrary signs before him instead\nof the appearances themselves; no modes of expression are here proposed\nfor his adoption which may be repeated for ever without the exercise\nof thought and without leading any one to think; but we invite him to\nexamine intelligible appearances, which must be present to the eye and\nmind, in order to enable him clearly to trace these appearances to\ntheir origin, and to explain them to himself and to others.\n\n\n[1] The date of the publication, 1810, is sometimes to be\nremembered.--T.\n\n[2] The forms in fig. 2, plate 1, when seen through a prism, are\nagain intended to exemplify this. In the plates to the original work\ncurvilinear figures are added, but the circles, fig. 1, in the same\nplate, may answer the same end.--T.\n\n[3] The author has before observed that colour is a degree of darkness,\nand he here means that increase of darkness, produced by transparent\nmediums, is, to a certain extent, increase of colour.--T.\n\n\n\n\nXVI.\n\n\n## DECREASE OF THE APPEARANCE OF COLOUR.\n\n\n\n243.\n\nWe need only take the five conditions (210) under which the appearance\nof colour increases in the contrary order, to produce the contrary or\ndecreasing state; it may be as well, however, briefly to describe and\nreview the corresponding modifications which are presented to the eye.\n\n244.\n\nAt the highest point of complete junction of the opposite edges, the\ncolours appear as follows (216):--\n\n    Yellow-red.  Blue.\n    Green.       Red.\n    Blue-red.    Yellow.\n\n245.\n\nWhere the junction is less complete, the appearance is as follows (214,\n215):--\n\n    Yellow-red.  Blue.\n    Yellow.      Blue-red.\n    Green.       Red.\n    Blue.        Yellow-red.\n    Blue-red.    Yellow.\n\nHere, therefore, the surface still appears completely coloured, but\nneither series is to be considered as an elementary series, always\ndeveloping itself in the same manner and in the same degrees; on the\ncontrary, they can and should be resolved into their elements; and, in\ndoing this, we become better acquainted with their nature and character.\n\n246.\n\nThese elements then are (199, 200, 201)--\n\n    Yellow-red.  Blue.\n    Yellow.      Blue-red.\n    White.       Black.\n    Blue.        Yellow-red.\n    Blue-red.    Yellow.\n\nHere the surface itself, the original object, which has been hitherto\ncompletely covered, and as it were lost, again appears in the centre of\nthe colours, asserts its right, and enables us fully to recognise the\nsecondary nature of the accessory images which exhibit themselves as\n\"edges\" and \"borders.\"--Note N.\n\n247.\n\nWe can make these edges and borders as narrow as we please; nay, we\ncan still have refraction in reserve after having done away with all\nappearance of colour at the boundary of the object.\n\nHaving now sufficiently investigated the exhibition of colour in this\nphenomenon, we repeat that we cannot admit it to be an elementary\nphenomenon. On the contrary, we have traced it to an antecedent and\na simpler one; we have derived it, in connexion with the theory of\nsecondary images, from the primordial phenomenon of light and darkness,\nas affected or acted upon by semi-transparent mediums. Thus prepared,\nwe proceed to describe the appearances which refraction produces on\ngrey and coloured objects, and this will complete the section of\nsubjective phenomena.\n\n\n\n\n## XVII — GREY OBJECTS DISPLACED BY REFRACTION.\n\n\n\n248.\n\nHitherto we have confined our attention to black and white objects\nrelieved on respectively opposite grounds, as seen through the prism,\nbecause the coloured edges and borders are most clearly displayed in\nsuch cases. We now repeat these experiments with grey objects, and\nagain find similar results.\n\n249.\n\nAs we called black the equivalent of darkness, and white the\nrepresentative of light (18), so we now venture to say that grey\nrepresents half-shadow, which partakes more or less of light and\ndarkness, and thus stands between the two. We invite the reader to call\nto mind the following facts as bearing on our present view.\n\n250.\n\nGrey objects appear lighter on a black than on a white ground (33);\nthey appear as a light on a black ground, and larger; as a dark on the\nwhite ground, and smaller. (16.)\n\n251.\n\nThe darker the grey the more it appears as a faint light on black, as a\nstrong dark on white, and _vice versâ_; hence the accessory images of\ndark-grey on black are faint, on white strong: so the accessory images\nof light-grey on white are faint, on black strong.\n\n252.\n\nGrey on black, seen through the prism, will exhibit the same\nappearances as white on black; the edges are coloured according to the\nsame law, only the borders appear fainter. If we relieve grey on white,\nwe have the same edges and borders which would be produced if we saw\nblack on white through the prism.--Note O.\n\n253.\n\nVarious shades of grey placed next each other in gradation will exhibit\nat their edges, either blue and violet only, or red and yellow only,\naccording as the darker grey is placed over or under.\n\n254.\n\nA series of such shades of grey placed horizontally next each other\nwill be coloured conformably to the same law according as the whole\nseries is relieved, on a black or white ground above or below.\n\n255.\n\nThe observer may see the phenomena exhibited by the prism at one\nglance, by enlarging the plate intended to illustrate this section.[1]\n\n256.\n\nIt is of great importance duly to examine and consider another\nexperiment in which a grey object is placed partly on a black and\npartly on a white surface, so that the line of division passes\nvertically through the object.\n\n257.\n\nThe colours will appear on this grey object in conformity with the\nusual law, but according to the opposite relation of the light to the\ndark, and will be contrasted in a line. For as the grey is as a light\nto the black, so it exhibits the red and yellow above the blue and\nviolet below: again, as the grey is as a dark to the white, the blue\nand violet appear above the red and yellow below. This experiment will\nbe found of great importance with reference to the next chapter.\n\n\n[1] It has been thought unnecessary to give all the examples in the\nplate alluded to, but the leading instance referred to in the next\nparagraph will be found in plate 3, fig. 1. The grey square when seen\nthrough a prism will exhibit the effects described in par. 257.--T.\n\n\n\n\n## XVIII.\n\n\n\n## COLOURED OBJECTS DISPLACED BY REFRACTION.\n\n\n\n258.\n\nAn unlimited coloured surface exhibits no prismatic colour in addition\nto its own hue, thus not at all differing from a black, white, or\ngrey surface. To produce the appearance of colour, light and dark\nboundaries must act on it either accidentally or by contrivance. Hence\nexperiments and observations on coloured surfaces, as seen through the\nprism, can only be made when such surfaces are separated by an outline\nfrom another differently tinted surface, in short when _circumscribed\nobjects_ are coloured.\n\n259.\n\nAll colours, whatever they may be, correspond so far with grey, that\nthey appear darker than white and lighter than black. This shade-like\nquality of colour (σκιέρον) has been already alluded to (69), and will\nbecome more and more evident. If then we begin by placing coloured\nobjects on black and white surfaces, and examine them through the\nprism, we shall again have all that we have seen exhibited with grey\nsurfaces.\n\n\n[Illustration]\n\n260.\n\nIf we displace a coloured object by refraction, there appears, as\nin the case of colourless objects and according to the same laws,\nan accessory image. This accessory image retains, as far as colour\nis concerned, its usual nature, and acts on one side as a blue and\nblue-red, on the opposite side as a yellow and yellow-red. Hence the\napparent colour of the edge and border will be either homogeneous\nwith the real colour of the object, or not so. In the first case the\napparent image identifies itself with the real one, and appears to\nincrease it, while, in the second case, the real image may be vitiated,\nrendered indistinct, and reduced in size by the apparent image. We\nproceed to review the cases in which these effects are most strikingly\nexhibited.\n\n261.\n\nIf we take a coloured drawing enlarged from the plate, which\nillustrates this experiment[1], and examine the red and blue squares\nplaced next each other on a black ground, through the prism as usual,\nwe shall find that as both colours are lighter than the ground,\nsimilarly coloured edges and borders will appear above and below, at\nthe outlines of both, only they will not appear equally distinct to the\neye.\n\n262.\n\nRed is proportionally much lighter on black than blue is. The colours\nof the edges will therefore appear stronger on the red than on the\nblue, which here acts as a dark-grey, but little different from black.\n(251.)\n\n263.\n\nThe extreme red edge will identify itself with the vermilion colour\nof the square, which will thus appear a little elongated in this\ndirection; while the yellow border immediately underneath it only gives\nthe red surface a more brilliant appearance, and is not distinguished\nwithout attentive observation.\n\n264.\n\nOn the other hand the red edge and yellow border are heterogeneous\nwith the blue square; a dull red appears at the edge, and a dull green\nmingles with the figure, and thus the blue square seems, at a hasty\nglance, to be comparatively diminished on this side.\n\n265.\n\nAt the lower outline of the two squares a blue edge and a violet border\nwill appear, and will produce the contrary effect; for the blue edge,\nwhich is heterogeneous with the warm red surface, will vitiate it\nand produce a neutral colour, so that the red on this side appears\ncomparatively reduced and driven upwards, and the violet border on the\nblack is scarcely perceptible.\n\n266.\n\nOn the other hand, the blue apparent edge will identify itself with the\nblue square, and not only not reduce, but extend it. The blue edge and\neven the violet border next it have the apparent effect of increasing\nthe surface, and elongating it in that direction.\n\n267.\n\nThe effect of homogeneous and heterogeneous edges, as I have now\nminutely described it, is so powerful and singular that the two squares\nat the first glance seem pushed out of their relative horizontal\nposition and moved in opposite directions, the red upwards, the blue\ndownwards. But no one who is accustomed to observe experiments in a\ncertain succession, and respectively to connect and trace them, will\nsuffer himself to be deceived by such an unreal effect.\n\n268.\n\nA just impression with regard to this important phenomenon will,\nhowever, much depend on some nice and even troublesome conditions,\nwhich are necessary to produce the illusion in question. Paper should\nbe tinged with vermilion or the best minium for the red square, and\nwith deep indigo for the blue square. The blue and red prismatic edges\nwill then unite imperceptibly with the real surfaces where they are\nrespectively homogeneous; where they are not, they vitiate the colours\nof the squares without producing a very distinct middle tint. The real\nred should not incline too much to yellow, otherwise the apparent deep\nred edge above will be too distinct; at the same time it should be\nsomewhat yellow, otherwise the transition to the yellow border will be\ntoo observable. The blue must not be light, otherwise the red edge will\nbe visible, and the yellow border will produce a too decided green,\nwhile the violet border underneath would not give us the impression of\nbeing part of an elongated light blue square.\n\n269.\n\nAll this will be treated more circumstantially hereafter, when we speak\nof the apparatus intended to facilitate the experiments connected with\nthis part of our subject.[2] Every inquirer should prepare the figures\nhimself, in order fairly to exhibit this specimen of ocular deception,\nand at the same time to convince himself that the coloured edges, even\nin this case, cannot escape accurate examination.\n\n270.\n\nMeanwhile various other combinations, as exhibited in the plate, are\nfully calculated to remove all doubt on this point in the mind of every\nattentive observer.\n\n271.\n\nIf, for instance, we look at a white square, next the blue one, on a\nblack ground, the prismatic hues of the opposite edges of the white,\nwhich here occupies the place of the red in the former experiment, will\nexhibit themselves in their utmost force. The red edge extends itself\nabove the level of the blue almost in a greater degree than was the\ncase with the red square itself in the former experiment. The lower\nblue edge, again, is visible in its full force next the white, while,\non the other hand, it cannot be distinguished next the blue square. The\nviolet border underneath is also much more apparent on the white than\non the blue.\n\n272.\n\nIf the observer now compares these double squares, carefully prepared\nand arranged one above the other, the red with the white, the two blue\nsquares together, the blue with the red, the blue with the white, he\nwill clearly perceive the relations of these surfaces to their coloured\nedges and borders.\n\n273.\n\nThe edges and their relations to the coloured surfaces appear still\nmore striking if we look at the coloured squares and a black square\non a white ground; for in this case the illusion before mentioned\nceases altogether, and the effect of the edges is as visible as in\nany case that has come under our observation. Let the blue and red\nsquares be first examined through the prism. In both the blue edge now\nappears above; this edge, homogeneous with the blue surface, unites\nwith it, and appears to extend it upwards, only the blue edge, owing\nto its lightness, is somewhat too distinct in its upper portion; the\nviolet border underneath it is also sufficiently evident on the blue.\nThe apparent blue edge is, on the other hand, heterogeneous with the\nred square; it is neutralised by contrast, and is scarcely visible;\nmeanwhile the violet border, uniting with the real red, produces a hue\nresembling that of the peach-blossom.\n\n274.\n\nIf thus, owing to the above causes, the upper outlines of these\nsquares do not appear level with each other, the correspondence of the\nunder outlines is the more observable; for since both colours, the red\nand the blue, are darks compared with the white (as in the former case\nthey were light compared with the black), the red edge with its yellow\nborder appears very distinctly under both. It exhibits itself under the\nwarm red surface in its full force, and under the dark blue nearly as\nit appears under the black: as may be seen if we compare the edges and\nborders of the figures placed one above the other on the white ground.\n\n275.\n\nIn order to present these experiments with the greatest variety and\nperspicuity, squares of various colours are so arranged[3] that the\nboundary of the black and white passes through them vertically.\nAccording to the laws now known to us, especially in their application\nto coloured objects, we shall find the squares as usual doubly coloured\nat each edge; each square will appear to be split in two, and to be\nelongated upwards or downwards. We may here call to mind the experiment\nwith the grey figure seen in like manner on the line of division\nbetween black and white (257).[4]\n\n276.\n\nA phenomenon was before exhibited, even to illusion, in the instance of\na red and blue square on a black ground; in the present experiment the\nelongation upwards and downwards of two differently coloured figures\nis apparent in the two halves of one and the same figure of one and\nthe same colour. Thus we are still referred to the coloured edges and\nborders, and to the effects of their homogeneous and heterogeneous\nrelations with respect to the real colours of the objects.\n\n277.\n\nI leave it to observers themselves to compare the various gradations\nof coloured squares, placed half on black half on white, only inviting\ntheir attention to the apparent alteration which takes place in\ncontrary directions; for red and yellow appear elongated upwards if\non a black ground, downwards if on a white; blue, downwards if on a\nblack ground, upwards if on a white. All which, however, is quite in\naccordance with the diffusely detailed examples above given.\n\n278.\n\nLet the observer now turn the figures so that the before-mentioned\nsquares placed on the line of division between black and white may\nbe in a horizontal series; the black above, the white underneath. On\nlooking at these squares through the prism, he will observe that the\nred square gains by the addition of two red edges; on more accurate\nexamination he will observe the yellow border on the red figure, and\nthe lower yellow border upon the white will be perfectly apparent.\n\n279.\n\nThe upper red edge on the blue square is on the other hand hardly\nvisible; the yellow border next it produces a dull green by mingling\nwith the figure; the lower red edge and the yellow border are displayed\nin lively colours.\n\n280.\n\nAfter observing that the red figure in these cases appears to gain by\nan addition on both sides, while the dark blue, on one side at least,\nloses something; we shall see the contrary effect produced by turning\nthe same figures upside down, so that the white ground be above, the\nblack below.\n\n281.\n\nFor as the homogeneous edges and borders now appear above and below\nthe blue square, this appears elongated, and a portion of the surface\nitself seems even more brilliantly coloured: it is only by attentive\nobservation that we can distinguish the edges and borders from the\ncolour of the figure itself.\n\n282.\n\nThe yellow and red squares, on the other hand, are comparatively\nreduced by the heterogeneous edges in this position of the figures,\nand their colours are, to a certain extent, vitiated. The blue edge\nin both is almost invisible. The violet border appears as a beautiful\npeach-blossom hue on the red, as a very pale colour of the same kind on\nthe yellow; both the lower edges are green; dull on the red, vivid on\nthe yellow; the violet border is but faintly perceptible under the red,\nbut is more apparent under the yellow.\n\n283.\n\nEvery inquirer should make it a point to be thoroughly acquainted with\nall the appearances here adduced, and not consider it irksome to follow\nout a single phenomenon through so many modifying circumstances. These\nexperiments, it is true, may be multiplied to infinity by differently\ncoloured figures, upon and between differently coloured grounds. Under\nall such circumstances, however, it will be evident to every attentive\nobserver that coloured squares only appear relatively altered, or\nelongated, or reduced by the prism, because an addition of homogeneous\nor heterogeneous edges produces an illusion. The inquirer will now\nbe enabled to do away with this illusion if he has the patience to\ngo through the experiments one after the other, always comparing the\neffects together, and satisfying himself of their correspondence.\n\nExperiments with coloured objects might have been contrived in various\nways: why they have been exhibited precisely in the above mode, and\nwith so much minuteness, will be seen hereafter. The phenomena,\nalthough formerly not unknown, were much misunderstood; and it was\nnecessary to investigate them thoroughly to render some portions of our\nintended historical view clearer.\n\n284.\n\nIn conclusion, we will mention a contrivance by means of which our\nscientific readers may be enabled to see these appearances distinctly\nat one view, and even in their greatest splendour. Cut in a piece of\npasteboard five perfectly similar square openings of about an inch,\nnext each other, exactly in a horizontal line: behind these openings\nplace five coloured glasses in the natural order, orange, yellow,\ngreen, blue, violet. Let the series thus adjusted be fastened in an\nopening of the camera obscura, so that the bright sky may be seen\nthrough the squares, or that the sun may shine on them; they will thus\nappear very powerfully coloured. Let the spectator now examine them\nthrough the prism, and observe the appearances, already familiar by\nthe foregoing experiments, with coloured objects, namely, the partly\nassisting, partly neutralising effects of the edges and borders, and\nthe consequent apparent elongation or reduction of the coloured squares\nwith reference to the horizontal line. The results witnessed by the\nobserver in this case, entirely correspond with those in the cases\nbefore analysed; we do not, therefore, go through them again in detail,\nespecially as we shall find frequent occasions hereafter to return to\nthe subject.--Note P.\n\n\n[1] Plate 3, fig. 1. The author always recommends making the\nexperiments on an increased scale, in order to see the prismatic\neffects distinctly.\n\n[2] Neither the description of the apparatus nor the recapitulation\nof the whole theory, so often alluded to by the author, were ever\ngiven.--T.\n\n[3] Plate 3. fig. 1.\n\n[4] The grey square is introduced in the same plate, fig. 1, above the\ncoloured squares.\n\n\n\n\nXIX.\n\n\n## ACHROMATISM AND HYPERCHROMATISM.\n\n\n\n285.\n\nFormerly when much that is regular and constant in nature was\nconsidered as mere aberration and accident, the colours arising from\nrefraction were but little attended to, and were looked upon as an\nappearance attributable to particular local circumstances.\n\n286.\n\nBut after it had been assumed that this appearance of colour\naccompanies refraction at all times, it was natural that it should\nbe considered as intimately and exclusively connected with that\nphenomenon; the belief obtaining that the measure of the coloured\nappearance was in proportion to the measure of the refraction, and that\nthey must advance _pari passu_ with each other.\n\n287.\n\nIf, again, philosophers ascribed the phenomenon of a stronger or weaker\nrefraction, not indeed wholly, but in some degree, to the different\ndensity of the medium, (as purer atmospheric air, air charged with\nvapours, water, glass, according to their increasing density, increase\nthe so-called refraction, or displacement of the object;) so they\ncould hardly doubt that the appearance of colour must increase in the\nsame proportion; and hence took it for granted, in combining different\nmediums which were to counteract refraction, that as long as refraction\nexisted, the appearance of colour must take place, and that as soon as\nthe colour disappeared, the refraction also must cease.\n\n288.\n\nAfterwards it was, however, discovered that this relation which was\nassumed to correspond, was, in fact, dissimilar; that two mediums can\nrefract an object with equal power, and yet produce very dissimilar\ncoloured borders.\n\n289.\n\nIt was found that, in addition to the physical principle to which\nrefraction was ascribed, a chemical one was also to be taken into the\naccount. We propose to pursue this subject hereafter, in the chemical\ndivision of our inquiry, and we shall have to describe the particulars\nof this important discovery in our history of the doctrine of colours.\nWhat follows may suffice for the present.\n\n290.\n\nIn mediums of similar or nearly similar refracting power, we find\nthe remarkable circumstance that a greater and lesser appearance of\ncolour can be produced by a chemical treatment; the greater effect is\nowing, namely, to acids, the lesser to alkalis. If metallic oxydes are\nintroduced into a common mass of glass, the coloured appearance through\nsuch glasses becomes greatly increased without any perceptible change\nof refracting power. That the lesser effect, again, is produced by\nalkalis, may be easily supposed.\n\n291.\n\nThose kinds of glass which were first employed after the discovery,\nare called flint and crown glass; the first produces the stronger, the\nsecond the fainter appearance of colour.\n\n292.\n\nWe shall make use of both these denominations as technical terms in our\npresent statement, and assume that the refractive power of both is\nthe same, but that flint-glass produces the coloured appearance more\nstrongly by one-third than the crown-glass. The diagram (Plate 3, fig.\n2,) may serve in illustration.\n\n293.\n\nA black surface is here divided into compartments for more convenient\ndemonstration: let the spectator imagine five white squares between the\nparallel lines _a, b,_ and _c, d_. The square No. 1, is presented to\nthe naked eye unmoved from its place.\n\n294.\n\nBut let the square No. 2, seen through a crown-glass prism _g_, be\nsupposed to be displaced by refraction three compartments, exhibiting\nthe coloured borders to a certain extent; again, let the square No. 3,\nseen through a flint glass prism _h_, in like manner be moved downwards\nthree compartments, when it will exhibit the coloured borders by about\na third wider than No. 2.\n\n295.\n\nAgain, let us suppose that the square No. 4, has, like No. 2, been\nmoved downwards three compartments by a prism of crown-glass, and that\nthen by an oppositely placed prism _h_, of flint-glass, it has been\nagain raised to its former situation, where it now stands.\n\n296.\n\nHere, it is true, the refraction is done away with by the opposition of\nthe two; but as the prism _h_, in displacing the square by refraction\nthrough three compartments, produces coloured borders wider by a\nthird than those produced by the prism _g_, so, notwithstanding the\nrefraction is neutralised, there must be an excess of coloured border\nremaining. (The position of this colour, as usual, depends on the\ndirection of the apparent motion (204) communicated to the square by\nthe prism _h_, and, consequently, it is the reverse of the appearance\nin the two squares 2 and 3, which have been moved in an opposite\ndirection.) This excess of colour we have called Hyperchromatism, and\nfrom this the achromatic state may be immediately arrived at.\n\n297.\n\nFor assuming that it was the square No. 5 which was removed three\ncompartments from its first supposed place, like No. 2, by a prism of\ncrown-glass _g_, it would only be necessary to reduce the angle of a\nprism of flint-glass _h_, and to connect it, reversed, to the prism\n_g_, in order to raise the square No. 5 two degrees or compartments;\nby which means the Hyperchromatism of the first case would cease, the\nfigure would not quite return to its first position, and yet be already\ncolourless. The prolonged lines of the united prisms, under No. 5, show\nthat a single complete prism remains: again, we have only to suppose\nthe lines curved, and an object-glass presents itself. Such is the\nprinciple of the achromatic telescopes.\n\n298.\n\nFor these experiments, a small prism composed of three different\nprisms, as prepared in England, is extremely well adapted. It is to be\nhoped our own opticians will in future enable every friend of science\nto provide himself with this necessary instrument.\n\n\n\n\nXX.\n\n\n## ADVANTAGES OF SUBJECTIVE EXPERIMENTS.--TRANSITION TO THE OBJECTIVE.\n\n\n\n299.\n\nWe have presented the appearances of colour as exhibited by refraction,\nfirst, by means of subjective experiments; and we have so far arrived\nat a definite result, that we have been enabled to deduce the phenomena\nin question from the doctrine of semi-transparent mediums and double\nimages.\n\n300.\n\nIn statements which have reference to nature, everything depends on\nocular inspection, and these experiments are the more satisfactory as\nthey may be easily and conveniently made. Every amateur can procure\nhis apparatus without much trouble or cost, and if he is a tolerable\nadept in pasteboard contrivances, he may even prepare a great part of\nhis machinery himself. A few plain surfaces, on which black, white,\ngrey, and coloured objects may be exhibited alternately on a light and\ndark ground, are all that is necessary. The spectator fixes them before\nhim, examines the appearances at the edge of the figures conveniently,\nand as long as he pleases; he retires to a greater distance, again\napproaches, and accurately observes the progressive states of the\nphenomena.\n\n301.\n\nBesides this, the appearances may be observed with sufficient exactness\nthrough small prisms, which need not be of the purest glass. The other\ndesirable requisites in these glass instruments will, however, be\npointed out in the section which treats of the apparatus.[1]\n\n302.\n\nA great advantage in these experiments, again, is, that they can be\nmade at any hour of the day in any room, whatever aspect it may have.\nWe have no need to wait for sunshine, which in general is not very\npropitious to northern observers.\n\n\n[1] This description of the apparatus was never given.\n\n\n\n\n## OBJECTIVE EXPERIMENTS.\n\n\n\n303.\n\nThe objective experiments, on the contrary, necessarily require the\nsun-light which, even when it is to be had, may not always have the\nmost desirable relation with the apparatus placed opposite to it.\nSometimes the sun is too high, sometimes too low, and withal only a\nshort time in the meridian of the best situated room. It changes its\ndirection during the observation, the observer is forced to alter\nhis own position and that of his apparatus, in consequence of which\nthe experiments in many cases become uncertain. If the sun shines\nthrough the prism it exhibits all inequalities, lines, and bubbles\nin the glass, and thus the appearance is rendered confused, dim, and\ndiscoloured.\n\n304.\n\nYet both kinds of experiments must be investigated with equal accuracy.\nThey appear to be opposed to each other, and yet are always parallel.\nWhat one order of experiments exhibits the other exhibits likewise,\nand yet each has its peculiar capabilities, by means of which certain\neffects of nature are made known to us in more than one way.\n\n305.\n\nIn the next place there are important phenomena which may be exhibited\nby the union of subjective and objective experiments. The latter\nexperiments again have this advantage, that we can in most cases\nrepresent them by diagrams, and present to view the component relations\nof the phenomena. In proceeding, therefore, to describe the objective\nexperiments, we shall so arrange them that they may always correspond\nwith the analogous subjective examples; for this reason, too, we annex\nto the number of each paragraph the number of the former corresponding\none. But we set out by observing generally that the reader must consult\nthe plates, that the scientific investigator must be familiar with the\napparatus in order that the twin-phenomena in one mode or the other may\nbe placed before them.\n\n\n\n\nXXI.\n\n\n## REFRACTION WITHOUT THE APPEARANCE OF COLOUR.\n\n\n\n306 (195, 196).\n\nThat refraction may exhibit its effects without producing an appearance\nof colour, is not to be demonstrated so perfectly in objective as\nin subjective experiments. We have, it is true, unlimited spaces\nwhich we can look at through the prism, and thus convince ourselves\nthat no colour appears where there is no boundary; but we have no\nunlimited source of light which we can cause to act through the prism.\nOur light comes to us from circumscribed bodies; and the sun, which\nchiefly produces our prismatic appearances, is itself only a small,\ncircumscribed, luminous object.\n\n307.\n\nWe may, however, consider every larger opening through which the sun\nshines, every larger medium through which the sun-light is transmitted\nand made to deviate from its course, as so far unlimited that we can\nconfine our attention to the centre of the surface without considering\nits boundaries.\n\n308 (197).\n\nIf we place a large water-prism in the sun, a large bright space is\nrefracted upwards by it on the plane intended to receive the image, and\nthe middle of this illumined space will be colourless. The same effect\nmay be produced if we make the experiment with glass prisms having\nangles of few degrees: the appearance may be produced even through\nglass prisms, whose refracting angle is sixty degrees, provided we\nplace the recipient surface near enough.\n\n\n\n\n## XXII.\n\n\n\n## CONDITIONS OF THE APPEARANCE OF COLOUR.\n\n\n\n309 (198).\n\nAlthough, then, the illumined space before mentioned appears indeed\nrefracted and moved from its place, but not coloured, yet on the\nhorizontal edges of this space we observe a coloured appearance.\nThat here again the colour is solely owing to the displacement of a\ncircumscribed object may require to be more fully proved.\n\nThe luminous body which here acts is circumscribed: the sun, while it\nshines and diffuses light, is still an insulated object. However small\nthe opening in the lid of a camera obscura be made, still the whole\nimage of the sun will penetrate it. The light which streams from all\nparts of the sun's disk, will cross itself in the smallest opening, and\nform the angle which corresponds with the sun's apparent diameter. On\nthe outside we have a cone narrowing to the orifice; within, this apex\nspreads again, producing on an opposite surface a round image, which\nstill increases in size in proportion to the distance of the recipient\nsurface from the apex. This image, together with all other objects\nof the external landscape, appears reversed on the white surface in\nquestion in a dark room.\n\n310.\n\nHow little therefore we have here to do with single sun-rays, bundles\nor fasces of rays, cylinders of rays, pencils, or whatever else of the\nkind may be imagined, is strikingly evident. For the convenience of\ncertain diagrams the sun-light may be assumed to arrive in parallel\nlines, but it is known that this is only a fiction; a fiction quite\nallowable where the difference between the assumption and the true\nappearance is unimportant; but we should take care not to suffer such a\npostulate to be equivalent to a fact, and proceed to further operations\non such a fictitious basis.\n\n311.\n\nLet the aperture in the window-shutter be now enlarged at pleasure, let\nit be made round or square, nay, let the whole shutter be opened, and\nlet the sun shine into the room through the whole window; the space\nwhich the sun illumines will always be larger according to the angle\nwhich its diameter makes; and thus even the whole space illumined by\nthe sun through the largest window is only the image of the sun _plus_\nthe size of the opening. We shall hereafter have occasion to return to\nthis.\n\n312 (199).\n\nIf we transmit the image of the sun through convex glasses we contract\nit towards the focus. In this case, according to the laws before\nexplained, a yellow border and a yellow-red edge must appear when the\nspectrum is thrown on white paper. But as this experiment is dazzling\nand inconvenient, it may be made more agreeably with the image of the\nfull moon. On contracting this orb by means of a convex glass, the\ncoloured edge appears in the greatest splendour; for the moon transmits\na mitigated light in the first instance, and can thus the more readily\nproduce colour which to a certain extent accompanies the subduing of\nlight: at the same time the eye of the observer is only gently and\nagreeably excited.\n\n313 (200).\n\nIf we transmit a luminous image through concave glasses, it is\ndilated. Here the image appears edged with blue.\n\n314.\n\nThe two opposite appearances may be produced by a convex glass,\nsimultaneously or in succession; simultaneously by fastening an opaque\ndisk in the centre of the convex glass, and then transmitting the sun's\nimage. In this case the luminous image and the black disk within it are\nboth contracted, and, consequently, the opposite colours must appear.\nAgain, we can present this contrast in succession by first contracting\nthe luminous image towards the focus, and then suffering it to expand\nagain beyond the focus, when it will immediately exhibit a blue edge.\n\n315 (201).\n\nHere too what was observed in the subjective experiments is again to be\nremarked, namely, that blue and yellow appear in and upon the white,\nand that both assume a reddish appearance in proportion as they mingle\nwith the black.\n\n316 (202, 203).\n\nThese elementary phenomena occur in all subsequent objective\nexperiments, as they constituted the groundwork of the subjective\nones. The process too which takes place is the same; a light boundary\nis carried over a dark surface, a dark surface is carried over a light\nboundary. The edges must advance, and as it were push over each other\nin these experiments as in the former ones.\n\n317 (204).\n\nIf we admit the sun's image through a larger or smaller opening into\nthe dark room, if we transmit it through a prism so placed that its\nrefracting angle, as usual, is underneath; the luminous image, instead\nof proceeding in a straight line to the floor, is refracted upwards on\na vertical surface placed to receive it. This is the moment to take\nnotice of the opposite modes in which the subjective and objective\nrefractions of the object appear.\n\n318.\n\nIf we _look_ through a prism, held with its refracting angle\nunderneath, at an object above us, the object is moved downwards;\nwhereas a luminous image refracted through the same prism is moved\nupwards. This, which we here merely mention as a matter of fact for\nthe sake of brevity, is easily explained by the laws of refraction and\nelevation.\n\n319.\n\nThe luminous object being moved from its place in this manner, the\ncoloured borders appear in the order, and according to the laws before\nexplained. The violet border is always foremost, and thus in objective\ncases proceeds upwards, in subjective cases downwards.\n\n320 (205).\n\nThe observer may convince himself in like manner of the mode in which\nthe appearance of colour takes place in the diagonal direction when the\ndisplacement is effected by means of two prisms, as has been plainly\nenough shown in the subjective example; for this experiment, however,\nprisms should be procured of few degrees, say about fifteen.\n\n321(206, 207).\n\nThat the colouring of the image takes place here too, according to the\ndirection in which it moves, will be apparent if we make a _square_\nopening of moderate size in a shutter, and cause the luminous image\nto pass through a water-prism; the spectrum being moved first in the\nhorizontal and vertical directions, then diagonally, the coloured edges\nwill change their position accordingly.\n\n322(208).\n\nWhence it is again evident that to produce colour the boundaries must\nbe carried over each other, not merely move side by side.\n\n\n\n\n## XXIII — CONDITIONS OF THE INCREASE OF COLOUR.\n\n\n\n323 (209).\n\nHere too an increased displacement of the object produces a greater\nappearance of colour.\n\n324 (210).\n\nThis increased displacement occurs,\n\n1. By a more oblique direction of the impinging luminous object through\nmediums with parallel surfaces.\n\n2. By changing the parallel form for one more or less acute angled.\n\n3. By increased proportion of the medium, whether parallel or acute\nangled; partly because the object is by this means more powerfully\ndisplaced, partly because an effect depending on the mere mass\nco-operates.\n\n4. By the distance of the recipient surface from the refracting medium\nso that the coloured spectrum emerging from the prism may be said to\nhave a longer way to travel.\n\n5. When a chemical property produces its effects under all these\ncircumstances: this we have already entered into more fully under the\nhead of achromatism and hyperchromatism.\n\n325 (211).\n\nThe objective experiments have this advantage that the progressive\nstates of the phenomenon may be arrested and clearly represented by\ndiagrams, which is not the case with the subjective experiments.\n\n326.\n\nWe can observe the luminous image after it has emerged from the prism,\nstep by step, and mark its increasing colour by receiving it on a\nplane at different distances, thus exhibiting before our eyes various\nsections of this cone, with an elliptical base: again, the phenomenon\nmay at once be rendered beautifully visible throughout its whole course\nin the following manner:--Let a cloud of fine white dust be excited\nalong the line in which the image passes through the dark space; the\ncloud is best produced by fine, perfectly dry, hair-powder. The more or\nless coloured appearance will now be painted on the white atoms, and\npresented in its whole length and breadth to the eye of the spectator.\n\n327.\n\nBy this means we have prepared some diagrams, which will be found among\nthe plates. In these the appearance is exhibited from its first origin,\nand by these the spectator can clearly comprehend why the luminous\nimage is so much more powerfully coloured through prisms than through\nparallel mediums.\n\n328 (212).\n\nAt the two opposite outlines of the image an opposite appearance\npresents itself, beginning from an acute angle;[1] the appearance\nspreads as it proceeds further in space, according to this angle. On\none side, in the direction in which the luminous image is moved, a\nviolet border advances on the dark, a narrower blue edge remains next\nthe outline of the image. On the opposite side a yellow border advances\ninto the light of the image itself, and a yellow-red edge remains at\nthe outline.\n\n329 (213).\n\nHere, therefore, the movement of the dark against the light, of the\nlight against the dark, may be clearly observed.\n\n\n[Illustration]\n\n330 (214).\n\nThe centre of a large object remains long uncoloured, especially with\nmediums of less density and smaller angles; but at last the opposite\nborders and edges touch each other, upon which a green appears in the\ncentre of the luminous image.\n\n331 (215).\n\nObjective experiments have been usually made with the sun's image: an\nobjective experiment with a dark object has hitherto scarcely been\nthought of. We have, however, prepared a convenient contrivance for\nthis also. Let the large water-prism before alluded to be placed in\nthe sun, and let a round pasteboard disk be fastened either inside or\noutside. The coloured appearance will again take place at the outline,\nbeginning according to the usual law; the edges will appear, they will\nspread in the same proportion, and when they meet, red will appear in\nthe centre[2]. An intercepting square may be added near the round disk,\nand placed in any direction _ad libitum_, and the spectator can again\nconvince himself of what has been before so often described.\n\n332 (216).\n\nIf we take away these dark objects from the prism, in which case,\nhowever, the glass is to be carefully cleaned, and hold a rod or a\nlarge pencil before the centre of the horizontal prism, we shall\nthen accomplish the complete immixture of the violet border and the\nyellow-red edge, and see only the three colours, the external blue, and\nyellow, and the central red.\n\n333.\n\nIf again we cut a long horizontal opening in the middle of a piece of\npasteboard, fastened on the prism, and then cause the sun-light to pass\nthrough it, we shall accomplish the complete union of the yellow border\nwith the blue edge upon the light, and only see yellow-red, green and\nviolet. The details of this are further entered into in the description\nof the plates.\n\n334 (217).\n\nThe prismatic appearance is thus by no means complete and final when\nthe luminous image emerges from the prism. It is then only that\nwe perceive its elements in contrast; for as it increases these\ncontrasting elements unite, and are at last intimately joined. The\nsection of this phenomenon arrested on a plane surface is different\nat every degree of distance from the prism; so that the notion of an\nimmutable series of colours, or of a pervading similar proportion\nbetween them, cannot be a question for a moment.\n\n\n[1] Plate 4. fig. 1.\n\n[2] Plate 4. fig. 2.\n\n\n\n\n## XXIV.\n\n\n\n## EXPLANATION OF THE FOREGOING PHENOMENA.\n\n\n\n335 (218).\n\nAs we have already entered into this analysis circumstantially while\ntreating of the subjective experiments, as all that was of force there\nis equally valid here, it will require no long details in addition to\nshow that the phenomena, which are entirely parallel in the two cases,\nmay also be traced precisely to the same sources.\n\n336 (219).\n\nThat in objective experiments also we have to do with circumscribed\nimages, has been already demonstrated at large. The sun may shine\nthrough the smallest opening, yet the image of the whole disk\npenetrates beyond. The largest prism may be placed in the open\nsun-light, yet it is still the sun's image that is bounded by the\nedges of the refracting surfaces, and produces the accessory images\nof this boundary. We may fasten pasteboard, with many openings cut in\nit, before the water-prism, yet we still merely see multiplied images\nwhich, after having been moved from their place by refraction, exhibit\ncoloured edges and borders, and in these mere accessory images.\n\n337 (235).\n\nIn subjective experiments we have seen that objects strongly relieved\nfrom each other produce a very lively appearance of colour, and this\nwill be the case in objective experiments in a much more vivid and\nsplendid degree. The sun's image is the most powerful brightness we\nknow; hence its accessory image will be energetic in proportion, and\nnotwithstanding its really secondary dimmed and darkened character,\nmust be still very brilliant. The colours thrown by the sun-light\nthrough the prism on any object, carry a powerful light with them, for\nthey have the highest and most intense source of light, as it were, for\ntheir ground.\n\n338.\n\nThat we are warranted in calling even these accessory images\nsemi-transparent, thus deducing the appearances from the doctrine\nof the semi-transparent mediums, will be clear to every one who has\nfollowed us thus far, but particularly to those who have supplied\nthemselves with the necessary apparatus, so as to be enabled at all\ntimes to witness the precision and vivacity with which semi-transparent\nmediums act.\n\n\n\n\nXXV.\n\n\n## DECREASE OF THE APPEARANCE OF COLOUR.\n\n\n\n339 (243).\n\nIf we could afford to be concise in the description of the decreasing\ncoloured appearance in subjective cases, we may here be permitted\nto proceed with still greater brevity while we refer to the former\ndistinct statement. One circumstance, only on account of its great\nimportance, may be here recommended to the reader's especial attention\nas a leading point of our whole thesis.\n\n340 (244, 247).\n\nThe decline of the prismatic appearance must be preceded by its\nseparation, by its resolution into its elements. At a due distance from\nthe prism, the image of the sun being entirely coloured, the blue and\nyellow at length mix completely, and we see only yellow-red, green, and\nblue-red. If we bring the recipient surface nearer to the refracting\nmedium, yellow and blue appear again, and we see the five colours with\ntheir gradations. At a still shorter distance the yellow and blue\nseparate from each other entirely, the green vanishes, and the image\nitself appears, colourless, between the coloured edges and borders. The\nnearer we bring the recipient surface to the prism, the narrower the\nedges and borders become, till at last, when in contact with the prism,\nthey are reduced to nothing.\n\n\n\n\n## XXVI.\n\n\n\n## GREY OBJECTS.\n\n\n\n341 (218).\n\nWe have exhibited grey objects as very important to our inquiry in the\nsubjective experiments. They show, by the faintness of the accessory\nimages, that these same images are in all cases derived from the\nprincipal object. If we wish here, too, to carry on the objective\nexperiments parallel with the others, we may conveniently do this by\nplacing a more or less dull ground glass before the opening through\nwhich the sun's image enters. By this means a subdued image would be\nproduced, which on being refracted would exhibit much duller colours on\nthe recipient plane than those immediately derived from the sun's disk;\nand thus, even from the intense sun-image, only a faint accessory image\nwould appear, proportioned to the mitigation of the light by the glass.\nThis experiment, it is true, will only again and again confirm what is\nalready sufficiently familiar to us.\n\n\n\n\n## XXVII.\n\n\n\n## COLOURED OBJECTS.\n\n\n\n342 (260).\n\nThere are various modes of producing coloured images in objective\nexperiments. In the first place, we can fix coloured glass before the\nopening, by which means a coloured image is at once produced; secondly,\nwe can fill the water-prism with coloured fluids; thirdly, we can cause\nthe colours, already produced in their full vivacity by the prism, to\npass through proportionate small openings in a tin plate, and thus\nprepare small circumscribed colours for a second operation. This last\nmode is the most difficult; for owing to the continual progress of the\nsun, the image cannot be arrested in any direction at will. The second\nmethod has also its inconveniences, since not all coloured liquids can\nbe prepared perfectly bright and clear. On these accounts the first is\nto be preferred, and deserves the more to be adopted because natural\nphilosophers have hitherto chosen to consider the colours produced\nfrom the sun-light through the prism, those produced through liquids\nand glasses, and those which are already fixed on paper or cloth, as\nexhibiting effects equally to be depended on, and equally available in\ndemonstration.\n\n343.\n\nAs it is thus merely necessary that the image should be coloured, so\nthe large water-prism before alluded to affords us the best means of\neffecting this. A pasteboard screen may be contrived to slide before\nthe large surfaces of the prism, through which, in the first instance,\nthe light passes uncoloured. In this screen openings of various forms\nmay be cut, in order to produce different images, and consequently\ndifferent accessory images. This being done, we need only fix coloured\nglasses before the openings, in order to observe what effect refraction\nproduces on coloured images in an objective sense.\n\n344.\n\nA series of glasses may be prepared in a mode similar to that before\ndescribed (284); these should be accurately contrived to slide in the\ngrooves of the large water-prism. Let the sun then shine through them,\nand the coloured images refracted upwards will appear bordered and\nedged, and will vary accordingly: for these borders and edges will be\nexhibited quite distinctly on some images, and on others will be mixed\nwith the specific colour of the glass, which they will either enhance\nor neutralize. Every observer will be enabled to convince himself\nhere again that we have only to do with the same simple phenomenon so\ncircumstantially described subjectively and objectively.\n\n\n\n\n## XXVIII.\n\n\n\n## ACHROMATISM AND HYPERCHROMATISM.\n\n\n\n345 (285, 290).\n\nIt is possible to make the hyperchromatic and achromatic experiments\nobjectively as well as subjectively. After what has been already\nstated, a short description of the method will suffice, especially as\nwe take it for granted that the compound prism before mentioned is in\nthe hands of the observer.\n\n346.\n\nLet the sun's image pass through an acute-angled prism of few degrees,\nprepared from crown-glass, so that the spectrum be refracted upwards on\nan opposite surface; the edges will appear coloured, according to the\nconstant law, namely, the violet and blue above and outside, the yellow\nand yellow-red below and within the image. As the refracting angle of\nthis prism is undermost, let another proportionate prism of flint-glass\nbe placed against it, with its refracting angle uppermost. The sun's\nimage will by this means be again moved to its place, where, owing to\nthe excess of the colouring power of the prism of flint-glass, it will\nstill appear a little coloured, and, in consequence of the direction\nin which it has been moved, the blue and violet will now appear\nunderneath and outside, the yellow and yellow-red above and inside.\n\n347.\n\nIf the whole image be now moved a little upwards by a proportionate\nprism of crown-glass, the hyperchromatism will disappear, the sun's\nimage will be moved from its place, and yet will appear colourless.\n\n348.\n\nWith an achromatic object-glass composed of three glasses, this\nexperiment may be made step by step, if we do not mind taking out the\nglasses from their setting. The two convex glasses of crown-glass in\ncontracting the sun's image towards the focus, the concave glass of\nflint-glass in dilating the image beyond it, exhibit at the edges the\nusual colours. A convex glass united with a concave one exhibits the\ncolours according to the law of the latter. If all three glasses are\nplaced together, whether we contract the sun's image towards the focus,\nor suffer it to dilate beyond the focus, coloured edges never appear,\nand the achromatic effect intended by the optician is, in this case,\nagain attained.\n\n349.\n\nBut as the crown-glass has always a greenish tint, and as a tendency\nto this hue may be more decided in large and strong object-glasses,\nand under certain circumstances produce the compensatory red,\n(which, however, in repeated experiments with several instruments of\nthis kind did not occur to us,) philosophers have resorted to the\nmost extraordinary modes of explaining such a result; and having\nbeen compelled, in support of their system, theoretically to prove\nthe impossibility of achromatic telescopes, have felt a kind of\nsatisfaction in having some apparent ground for denying so great an\nimprovement. Of this, however, we can only treat circumstantially in\nour historical account of these discoveries.\n\n\n\n\n## XXIX.\n\n\n\n## COMBINATION OF SUBJECTIVE AND OBJECTIVE EXPERIMENTS.\n\n\n\n350.\n\nHaving shown above (318) that refraction, considered objectively and\nsubjectively, must act in opposite directions, it will follow that if\nwe combine the experiments, the effects will reciprocally destroy each\nother.\n\n351.\n\nLet the sun's image be thrown upwards on a vertical plane, through\na horizontally-placed prism. If the prism is long enough to admit of\nthe spectator also looking through it, he will see the image elevated\nby the objective refraction again depressed, and in the same place in\nwhich it appeared without refraction.\n\n352.\n\nHere a remarkable case presents itself, but at the same time a natural\nresult of a general law. For since, as often before stated, the\nobjective sun's image thrown on the vertical plane is not an ultimate\nor unchangeable state of the phenomenon, so in the above operation the\nimage is not only depressed when seen through the prism, but its edges\nand borders are entirely robbed of their hues, and the spectrum is\nreduced to a colourless circular form.\n\n353.\n\nBy employing two perfectly similar prisms placed next each other, for\nthis experiment, we can transmit the sun's image through one, and look\nthrough the other.\n\n354.\n\nIf the spectator advances nearer with the prism through which he looks,\nthe image is again elevated, and by degrees becomes coloured according\nto the law of the first prism. If he again retires till he has brought\nthe image to the neutralized point, and then retires still farther\naway, the image, which had become round and colourless, moves still\nmore downwards and becomes coloured in the opposite sense, so that\nif we look through the prism and upon the refracted spectrum at the\nsame time, we see the same image coloured according to subjective and\nobjective laws.\n\n355.\n\nThe modes in which this experiment may be varied are obvious. If the\nrefracting angle of the prism, through which the sun's image was\nobjectively elevated, is greater than that of the prism through which\nthe observer looks, he must retire to a much greater distance, in order\nto depress the coloured image so low on the vertical plane that it\nshall appear colourless, and _vice versâ_.\n\n356.\n\nIt will be easily seen that we may exhibit achromatic and\nhyperchromatic effects in a similar manner, and we leave it to the\namateur to follow out such researches more fully. Other complicated\nexperiments in which prisms and lenses are employed together, others\nagain, in which objective and subjective experiments are variously\nintermixed, we reserve for a future occasion, when it will be our\nobject to trace such effects to the simple phenomena with which we are\nnow sufficiently familiar.\n\n\n\n\nXXX.\n\n\n## TRANSITION.\n\n\n\n357.\n\nIn looking back on the description and analysis of dioptrical colours,\nwe do not repent either that we have treated them so circumstantially,\nor that we have taken them into consideration before the other physical\ncolours, out of the order we ourselves laid down. Yet, before we quit\nthis branch of our inquiry, it may be as well to state the reasons that\nhave weighed with us.\n\n358.\n\nIf some apology is necessary for having treated the theory of the\ndioptrical colours, particularly those of the second class, so\ndiffusely, we should observe, that the exposition of any branch of\nknowledge is to be considered partly with reference to the intrinsic\nimportance of the subject, and partly with reference to the particular\nnecessities of the time in which the inquiry is undertaken. In our\nown case we were forced to keep both these considerations constantly\nin view. In the first place we had to state a mass of experiments with\nour consequent convictions; next, it was our especial aim to exhibit\ncertain phenomena (known, it is true, but misunderstood, and above\nall, exhibited in false connection,) in that natural and progressive\ndevelopment which is strictly and truly conformable to observation; in\norder that hereafter, in our polemical or historical investigations,\nwe might be enabled to bring a complete preparatory analysis to bear\non, and elucidate, our general view. The details we have entered into\nwere on this account unavoidable; they may be considered as a reluctant\nconsequence of the occasion. Hereafter, when philosophers will look\nupon a simple principle as simple, a combined effect as combined; when\nthey will acknowledge the first elementary, and the second complicated\nstates, for what they are; then, indeed, all this statement may be\nabridged to a narrower form; a labour which, should we ourselves\nnot be able to accomplish it, we bequeath to the active interest of\ncontemporaries and posterity.\n\n359.\n\nWith respect to the order of the chapters, it should be remembered\nthat natural phenomena, which are even allied to each other, are\nnot connected in any particular sequence or constant series; their\nefficient causes act in a narrow circle, so that it is in some sort\nindifferent what phenomenon is first or last considered; the main point\nis, that all should be as far as possible present to us, in order that\nwe may embrace them at last from one point of view, partly according to\ntheir nature, partly according to generally received methods.\n\n360.\n\nYet, in the present particular instance, it may be asserted that the\ndioptrical colours are justly placed at the head of the physical\ncolours; not only on account of their striking splendour and their\nimportance in other respects, but because, in tracing these to their\nsource, much was necessarily entered into which will assist our\nsubsequent enquiries.\n\n361.\n\nFor, hitherto, light has been considered as a kind of abstract\nprinciple, existing and acting independently; to a certain extent\nself-modified, and on the slightest cause, producing colours out of\nitself. To divert the votaries of physical science from this mode\nof viewing the subject; to make them attentive to the fact, that in\nprismatic and other appearances we have not to do with light as an\nuncircumscribed and modifying principle, but as circumscribed and\nmodified; that we have to do with a luminous image; with images or\ncircumscribed objects generally, whether light or dark: this was the\npurpose we had in view, and such is the problem to be solved.\n\n362.\n\nAll that takes place in dioptrical cases,--especially those of the\nsecond class which are connected with the phenomena of refraction,--is\nnow sufficiently familiar to us, and will serve as an introduction to\nwhat follows.\n\n363.\n\nCatoptrical appearances remind us of the physiological phenomena, but\nas we ascribe a more objective character to the former, we thought\nourselves justified in classing them with the physical examples. It is\nof importance, however, to remember that here again it is not light, in\nan abstract sense, but a luminous image that we have to consider.\n\n364.\n\nIn proceeding onwards to the paroptrical class, the reader, if duly\nacquainted with the foregoing facts, will be pleased to find himself\nonce more in the region of circumscribed forms. The shadows of bodies,\nespecially, as secondary images, so exactly accompanying the object,\nwill serve greatly to elucidate analogous appearances.\n\n365.\n\nWe will not, however, anticipate these statements, but proceed as\nheretofore in what we consider the regular course.\n\n\n\n\n## XXXI.\n\n\n\n## CATOPTRICAL COLOURS.\n\n\n\n366.\n\nCatoptrical colours are such as appear in consequence of a mirror-like\nreflection. We assume, in the first place, that the light itself\nas well as the surface from which it is reflected, is perfectly\ncolourless. In this sense the appearances in question come under the\nhead of physical colours. They arise in consequence of reflection, as\nwe found the dioptrical colours of the second class appear by means of\nrefraction. Without further general definitions, we turn our attention\nat once to particular cases, and to the conditions which are essential\nto the exhibition of these phenomena.\n\n367.\n\nIf we unroll a coil of bright steel-wire, and after suffering it to\nspring confusedly together again, place it at a window in the light,\nwe shall see the prominent parts of the circles and convolutions\nillumined, but neither resplendent nor iridescent. But if the sun\nshines on the wire, this light will be condensed into a point, and we\nperceive a small resplendent image of the sun, which, when seen near,\nexhibits no colour. On retiring a little, however, and fixing the eyes\non this refulgent appearance, we discern several small mirrored suns,\ncoloured in the most varied manner; and although the impression is that\ngreen and red predominate, yet, on a more accurate inspection, we find\nthat the other colours are also present.\n\n368.\n\nIf we take an eye-glass, and examine the appearance through it, we\nfind the colours have vanished, as well as the radiating splendour in\nwhich they were seen, and we perceive only the small luminous points,\nthe repeated images of the sun. We thus find that the impression is\nsubjective in its nature, and that the appearance is allied to those\nwhich we have adverted to under the name of radiating halos (100).\n\n369.\n\nWe can, however, exhibit this phenomenon objectively. Let a piece\nof white paper be fastened beneath a small aperture in the lid of a\ncamera-obscura, and when the sun shines through this aperture, let\nthe confusedly-rolled steel-wire be held in the light, so that it be\nopposite to the paper. The sun-light will impinge on and in the circles\nof the wire, and will not, as in the concentrating lens of the eye,\ndisplay itself in a point; but, as the paper can receive the reflection\nof the light in every part of its surface will be seen in hair-like\nlines, which are also iridescent.\n\n370.\n\nThis experiment is purely catoptrical; for as we cannot imagine that\nthe light penetrates the surface of the steel, and thus undergoes a\nchange, we are soon convinced that we have here a mere reflection\nwhich, in its subjective character, is connected with the theory of\nfaintly acting lights, and the after-image of dazzling lights, and as\nfar as it can be considered objective, announces even in the minutest\nappearances, a real effect, independent of the action and reaction of\nthe eye.\n\n371.\n\nWe have seen that to produce these effects not merely light but a\npowerful light is necessary; that this powerful light again is not an\nabstract and general quality, but a circumscribed light, a luminous\nimage. We can convince ourselves still further of this by analogous\ncases.\n\n372.\n\nA polished surface of silver placed in the sun reflects a dazzling\nlight, but in this case no colour is seen. If, however, we slightly\nscratch the surface, an iridescent appearance, in which green and red\nare conspicuous, will be exhibited at a certain angle. In chased and\ncarved metals the effect is striking: yet it may be remarked throughout\nthat, in order to its appearance, some form, some alternation of light\nand dark must co-operate with the reflection; thus a window-bar,\nthe stem of a tree, an accidentally or purposely interposed object\nproduces a perceptible effect. This appearance, too, may be exhibited\nobjectively in the camera-obscura.\n\n373.\n\nIf we cause a polished plated surface to be so acted on by aqua fortis\nthat the copper within is touched, and the surface itself thus rendered\nrough, and if the sun's image be then reflected from it, the splendour\nwill be reverberated from every minutest prominence, and the surface\nwill appear iridescent. So, if we hold a sheet of black unglazed paper\nin the sun, and look at it attentively, it will be seen to glisten in\nits minutest points with the most vivid colours.\n\n374.\n\nAll these examples are referable to the same conditions. In the first\ncase the luminous image is reflected from a thin line; in the second\nprobably from sharp edges; in the third from very small points. In all\na very powerful and circumscribed light is requisite. For all these\nappearances of colour again it is necessary that the eye should be at a\ndue distance from the reflecting points.\n\n375.\n\nIf these observations are made with the microscope, the appearance\nwill be greatly increased in force and splendour, for we then see the\nsmallest portion of the surfaces, lit by the sun, glittering in these\ncolours of reflection, which, allied to the hues of refraction, now\nattain their highest degree of brilliancy. In such cases we may observe\na vermiform iridescence on the surface of organic bodies, the further\ndescription of which will be given hereafter.\n\n376.\n\nLastly, the colours which are chiefly exhibited in reflection are red\nand green, whence we may infer that the linear appearance especially\nconsists of a thin line of red, bounded by blue on one side and yellow\non the other. If these triple lines approach very near together, the\nintermediate space must appear green; a phenomenon which will often\noccur to us as we proceed.\n\n377.\n\nWe frequently meet with these colours in nature. The colours of the\nspider's web might be considered exactly of the same class with those\nreflected from the steel wire, except that the non-translucent quality\nof the former is not so certain as in the case of steel; on which\naccount some have been inclined to class the colours of the spider's\nweb with the phenomena of refraction.\n\n378.\n\nIn mother-of-pearl we perceive infinitely fine organic fibres and\nlamellæ in juxta-position, from which, as from the scratched silver\nbefore alluded to, varied colours, but especially red and green, may\narise.\n\n379.\n\nThe changing colours of the plumage of birds may also be mentioned\nhere, although in all organic instances a chemical principle\nand an adaptation of the colour to the structure may be assumed;\nconsiderations to which we shall return in treating of chemical colours.\n\n380.\n\nThat the appearances of objective halos also approximate catoptrical\nphenomena will be readily admitted, while we again do not deny that\nrefraction as well may here come into the account. For the present\nwe restrict ourselves to one or two observations; hereafter we may\nbe enabled to make a fuller application of general principles to\nparticular examples.\n\n381.\n\nWe first call to mind the yellow and red circles produced on a white or\ngrey wall by a light placed near it (88). Light when reflected appears\nsubdued, and a subdued light excites the impression of yellow, and\nsubsequently of red.\n\n382.\n\nLet the wall be illumined by a candle placed quite close to it. The\nfarther the light is diffused the fainter it becomes; but it is still\nthe effect of the flame, the continuation of its action, the dilated\neffect of its image. We might, therefore, very fairly call these\ncircles reiterated images, because they constitute the successive\nboundaries of the action of the light, and yet at the same time only\npresent an extended image of the flame.\n\n383.\n\nIf the sky is white and luminous round the sun owing to the atmosphere\nbeing filled with light vapours; if mists or clouds pass before the\nmoon, the reflection of the disk mirrors itself in them; the halos we\nthen perceive are single or double, smaller or greater, sometimes very\nlarge, often colourless, sometimes coloured.\n\n384.\n\nI witnessed a very beautiful halo round the moon the 15th of November,\n1799, when the barometer stood high; the sky was cloudy and vapoury.\nThe halo was completely coloured, and the circles were concentric round\nthe light as in subjective halos. That this halo was objective I was\npresently convinced by covering the moon's disk, when the same circles\nwere nevertheless perfectly visible.\n\n385.\n\nThe different extent of the halos appears to have a relation with the\nproximity or distance of the vapour from the eye of the observer.\n\n386.\n\nAs window-panes lightly breathed upon increase the brilliancy of\nsubjective halos, and in some degree give them an objective character,\nso, perhaps, with a simple contrivance in winter, during a quickly\nfreezing temperature, a more exact definition of this might be arrived\nat.\n\n387.\n\nHow much reason we have in considering these circles to insist on the\n_image_ and its effects, is apparent in the phenomenon of the so-called\ndouble suns. Similar double images always occur in certain points\nof halos and circles, and only present in a circumscribed form what\ntakes place in a more general way in the whole circle. All this will\nbe more conveniently treated in connexion with the appearance of the\nrainbow.--Note Q.\n\n388.\n\nIn conclusion it is only necessary to point out the affinity between\nthe catoptrical and paroptical colours.\n\nWe call those paroptical colours which appear when the light passes\nby the edge of an opaque colourless body. How nearly these are allied\nto the dioptrical colours of the second class will be easily seen by\nthose who are convinced with us that the colours of refraction [Pg 163]\ntake place only at the edges of objects. The affinity again between the\ncatoptrical and paroptical colours will be evident in the following\nchapter.\n\n\n\n\n## XXXII.\n\n\n\n## PAROPTICAL COLOURS.\n\n\n\n389.\n\nThe paroptical colours have been hitherto called peri-optical, because\na peculiar effect of light was supposed to take place as it were round\nthe object, and was ascribed to a certain flexibility of the light to\nand from the object.\n\n390.\n\nThese colours again may be divided into subjective and objective,\nbecause they appear partly without us, as it were, painted on surfaces,\nand partly within us, immediately on the retina. In this chapter we\nshall find it more to our purpose to take the objective cases first,\nsince the subjective are so closely connected with other appearances\nalready known to us, that it is hardly possible to separate them.\n\n391.\n\nThe paroptical colours then are so called because the light must pass\nby an outline or edge to produce them. They do not, however, always\nappear in this case; to produce the effect very particular conditions\nare necessary besides.\n\n392.\n\nIt is also to be observed that in this instance again light does not\nact as an abstract diffusion (361), the sun shines towards an edge.\nThe volume of light poured from the sun-image passes by the edge of\na substance, and occasions shadows. Within these shadows we shall\npresently find colours appear.\n\n393.\n\nBut, above all, we should make the experiments and observations that\nbear upon our present inquiry in the fullest light. We, therefore,\nplace the observer in the open air before we conduct him to the limits\nof a dark room.\n\n394.\n\nA person walking in sun-shine in a garden, or on any level path, may\nobserve that his shadow only appears sharply defined next the foot on\nwhich he rests; farther from this point, especially round the head, it\nmelts away into the bright ground. For as the sun-light proceeds not\nonly from the middle of the sun, but also acts cross-wise from the two\nextremes of every diameter, an objective parallax takes place which\nproduces a half-shadow on both sides of the object.\n\n395.\n\nIf the person walking raises and spreads his hand, he distinctly sees\nin the shadow of each finger the diverging separation of the two\nhalf-shadows outwards, and the diminution of the principal shadow\ninwards, both being effects of the cross action of the light.\n\n396.\n\nThis experiment may be repeated and varied before a smooth wall,\nwith rods of different thicknesses, and again with balls; we shall\nalways find that the farther the object is removed from the surface of\nthe wall, the more the weak double shadow spreads, and the more the\nforcible main shadow diminishes, till at last the main shadow appears\nquite effaced, and even the double shadows become so faint, that they\nalmost disappear; at a still greater distance they are, in fact,\nimperceptible.\n\n397.\n\nThat this is caused by the cross-action of the light we may easily\nconvince ourselves; for the shadow of a pointed object plainly exhibits\ntwo points. We must thus never lose sight of the fact that in this\ncase the whole sun-image acts, produces shadows, changes them to double\nshadows, and finally obliterates them.\n\n398.\n\nInstead of solid bodies let us now take openings cut of various given\nsizes next each other, and let the sun shine through them on a plane\nsurface at some little distance; we shall find that the bright image\nproduced by the sun on the surface, is larger than the opening; this\nis because one edge of the sun shines towards the opposite edge of the\nopening, while the other edge of the disk is excluded on that side.\nHence the bright image is more weakly lighted towards the edges.\n\n399.\n\nIf we take square openings of any size we please, we shall find that\nthe bright image on a surface nine feet from the opening, is on every\nside about an inch larger than the opening; thus nearly corresponding\nwith the angle of the apparent diameter of the sun.\n\n400.\n\nThat the brightness should gradually diminish towards the edges of the\nimage is quite natural, for at last only a minimum of the light can\nact cross-wise from the sun's circumference through the edge of the\naperture.\n\n401.\n\nThus we here again see how much reason we have in actual observation to\nguard against the assumption of parallel rays, bundles and fasces of\nrays, and the like hypothetical notions.\n\n402.\n\nWe might rather consider the splendour of the sun, or of any light,\nas an infinite specular multiplication of the circumscribed luminous\nimage, whence it may be explained that all square openings through\nwhich the sun shines, at certain distances, according as the apertures\nare greater or smaller, must give a round image of light.\n\n403.\n\nThe above experiments may be repeated through openings of various\nshapes and sizes, and the same effect will always take place at\nproportionate distances. In all these cases, however, we may still\nobserve that in a full light and while the sun merely shines past an\nedge, no colour is apparent.\n\n404.\n\nWe therefore proceed to experiments with a subdued light, which is\nessential to the appearance of colour. Let a small opening be made in\nthe window-shutter of a dark room; let the crossing sun-light which\nenters, be received on a surface of white paper, and we shall find that\nthe smaller the opening is, the dimmer the light image will be. This is\nquite obvious, because the paper does not receive light from the whole\nsun, but partially from single points of its disk.\n\n405.\n\nIf we look attentively at this dim image of the sun, we find it still\ndimmer towards the outlines where a yellow border is perceptible. The\ncolour is still more apparent if a vapour or a transparent cloud passes\nbefore the sun, thus subduing and dimming its brightness. The halo on\nthe wall, the effect of the decreasing brightness of a light placed\nnear it, is here forced on our recollection. (88.)\n\n406.\n\nIf we examine the image more accurately, we perceive that this yellow\nborder is not the only appearance of colour; we can see, besides, a\nbluish circle, if not even a halo-like repetition of the coloured\nborder. If the room is quite dark, we discern that the sky next the\nsun also has its effect: we see the blue sky, nay, even the whole\nlandscape, on the paper, and are thus again convinced that as far as\nregards the sun, we have here only to do with a luminous image.\n\n407.\n\nIf we take a somewhat larger square opening, so large that the image\nof the sun shining through it does not immediately become round, we\nmay distinctly observe the half-shadows of every edge or side, the\njunction of these in the corners, and their colours; just as in the\nabove-mentioned appearance with the round opening.\n\n408.\n\nWe have now subdued a parallactic light by causing it to shine through\nsmall apertures, but we have not taken from it its parallactic\ncharacter; so that it can produce double shadows of bodies, although\nwith diminished power. These double shadows which we have hitherto\nbeen describing, follow each other in light and dark, coloured and\ncolourless circles, and produce repeated, nay, almost innumerable\nhalos. These effects have been often represented in drawings and\nengravings. By placing needles, hairs, and other small bodies, in the\nsubdued light, the numerous halo-like double shadows may be increased;\nthus observed, they have been ascribed to an alternating flexile action\nof the light, and the same assumption has been employed to explain the\nobliteration of the central shadow, and the appearance of a light in\nthe place of the dark.\n\n409.\n\nFor ourselves, we maintain that these again are parallactic double\nshadows, which appear edged with coloured borders and halos.\n\n410.\n\nAfter having seen and investigated the foregoing phenomena, we\ncan proceed to the experiments with knife-blades,[1] exhibiting\neffects which may be referred to the contact and parallactic mutual\nintersection of the half-shadows and halos already familiar to us.\n\n411.\n\nLastly, the observer may follow out the experiments with hairs,\nneedles, and wires, in the half-light produced as before described by\nthe sun, as well as in that derived from the blue sky, and indicated on\nthe white paper. He will thus make himself still better acquainted with\nthe true nature of this phenomenon.\n\n412.\n\nBut since in these experiments everything depends on our being\npersuaded of the parallactic action of the light, we can make this more\nevident by means of two sources of light, the two shadows from which\nintersect each other, and may be altogether separated. By day this may\nbe contrived with two small openings in a window-shutter; by night,\nwith two candles. There are even accidental effects in interiors, on\nopening and closing shutters, by means of which we can better observe\nthese appearances than with the most careful apparatus. But still,\nall and each of these may be reduced to experiment by preparing a box\nwhich the observer can look into from above, and gradually diminishing\nthe openings after having caused a double light to shine in. In this\ncase, as might be expected, the coloured shadow, considered under the\nphysiological colours, appears very easily.\n\n413.\n\nIt is necessary to remember, generally, what has been before stated\nwith regard to the nature of double shadows, half-lights, and the like.\nExperiments also should especially be made with different shades of\ngrey placed next each other, where every stripe will appear light by a\ndarker, and dark by a lighter stripe next it. If at night, with three\nor more lights, we produce shadows which cross each other successively,\nwe can observe this phenomenon very distinctly, and we shall be\nconvinced that the physiological case before more fully treated, here\ncomes into the account (38).\n\n414.\n\nTo what extent the appearances that accompany the paroptical colours,\nmay be derived from the doctrine of subdued lights, from half-shadows,\nand from the physiological disposition of the retina, or whether we\nshall be forced to take refuge in certain intrinsic qualities of light,\nas has hitherto been done, time may teach. Suffice it here to have\npointed out the conditions under which the paroptical colours appear,\nand we may hope that our allusion to their connexion with the facts\nbefore adduced by us will not remain unnoticed by the observers of\nnature.\n\n415.\n\nThe affinity of the paroptical colours with the dioptrical of the\nsecond class will also be readily seen and followed up by every\nreflecting investigator. Here, as in those instances, we have to do\nwith edges or boundaries; here, as in those instances, with a light,\nwhich appears at the outline. How natural, therefore, it is to conclude\nthat the paroptical effects may be heightened, strengthened, and\nenriched by the dioptrical. Since, however, the luminous image actually\nshines through the medium, we can here only have to do with objective\ncases of refraction: it is these which are strictly allied to the\nparoptical cases. The subjective cases of refraction, where we see\nobjects through the medium, are quite distinct from the paroptical.\nWe have already recommended them on account of their clearness and\nsimplicity.\n\n416.\n\nThe connexion between the paroptical colours and the catoptrical may\nbe already inferred from what has been said: for as the catoptrical\ncolours only appear on scratches, points, steel-wire, and delicate\nthreads, so it is nearly the same case as if the light shone past an\nedge. The light must always be reflected from an edge in order to\nproduce colour. Here again, as before pointed out, the partial action\nof the luminous image and the subduing of the light are both to be\ntaken into the account.\n\n417.\n\nWe add but few observations on the subjective paroptical colours,\nbecause these may be classed partly with the physiological colours,\npartly with the dioptrical of the second order. The greater part hardly\nseem to belong here, but, when attentively considered, they still\ndiffuse a satisfactory light over the whole doctrine, and establish its\nconnexion.\n\n418.\n\nIf we hold a ruler before the eyes so that the flame of a light just\nappears above it, we see the ruler as it were indented and notched\nat the place where the light appears. This seems deducible from the\nexpansive power of light acting on the retina (18).\n\n419.\n\nThe same phenomenon on a large scale is exhibited at sun-rise; for when\nthe orb appears distinctly, but not too powerfully, so that we can\nstill look at it, it always makes a sharp indentation in the horizon.\n\n420.\n\nIf, when the sky is grey, we approach a window, so that the dark cross\nof the window-bars be relieved on the sky; if after fixing the eyes on\nthe horizontal bar we bend the head a little forward; on half closing\nthe eyes as we look up, we shall presently perceive a bright yellow-red\nborder under the bar, and a bright light-blue one above it. The duller\nand more monotonous the grey of the sky, the more dusky the room, and,\nconsequently, the more previously unexcited the eye, the livelier the\nappearance will be; but it may be seen by an attentive observer even in\nbright daylight.\n\n421.\n\nIf we move the head backwards while half closing the eyes, so that the\nhorizontal bar be seen below, the phenomenon will appear reversed. The\nupper edge will appear yellow, the under edge blue.\n\n422.\n\nSuch observations are best made in a dark room. If white paper is\nspread before the opening where the solar microscope is commonly\nfastened, the lower edge of the circle will appear blue, the upper\nyellow, even while the eyes are quite open, or only by half-closing\nthem so far that a halo no longer appears round the white. If the head\nis moved backwards the colours are reversed.\n\n423.\n\nThese phenomena seem to prove that the humours of the eye are in fact\nonly really achromatic in the centre where vision takes place, but that\ntowards the circumference, and in unusual motions of the eyes, as in\nlooking horizontally when the head is bent backwards or forwards, a\nchromatic tendency remains, especially when distinctly relieved objects\nare thus looked at. Hence such phenomena may be considered as allied to\nthe dioptrical colours of the second class.\n\n424.\n\nSimilar colours appear if we look on black and white objects, through a\npin-hole in a card. Instead of a white object we may take the minute\nlight aperture in the tin plate of a camera obscura, as prepared for\nparoptical experiments.\n\n425.\n\nIf we look through a tube, the farther end of which is contracted or\nvariously indented, the same colours appear.\n\n426.\n\nThe following phenomena appear to me to be more nearly allied to the\nparoptical appearances. If we hold up a needle near the eye, the point\nappears double. A particularly remarkable effect again is produced if\nwe look towards a grey sky through the blades of knives prepared for\nparoptical experiments. We seem to look through a gauze; a multitude of\nthreads appear to the eye; these are in fact only the reiterated images\nof the sharp edges, each of which is successively modified by the next,\nor perhaps modified in a parallactic sense by the oppositely acting\none, the whole mass being thus changed to a thread-like appearance.\n\n427.\n\nLastly, it is to be remarked that if we look through the blades towards\na minute light in the window-shutter, coloured stripes and halos\nappear on the retina as on the paper.\n\n428.\n\nThe present chapter may be here terminated, the less reluctantly,\nas a friend has undertaken to investigate this subject by further\nexperiments. In our recapitulation, in the description of the\nplates and apparatus, we hope hereafter to give an account of his\nobservations.[2]\n\n\n[1] See Newton's Optics, book iii.\n\n[2] The observations here alluded to never appeared.\n\n\n\n\n## XXXIII.\n\n\n\n## EPOPTICAL COLOURS.\n\n\n\n429.\n\nWe have hitherto had to do with colours which appear with vivacity, but\nwhich immediately vanish again when certain conditions cease. We have\nnow to become acquainted with others, which it is true are still to be\nconsidered as transient, but which, under certain circumstances, become\nso fixed that, even after the conditions which first occasioned their\nappearance cease, they still remain, and thus constitute the link\nbetween the physical and the chemical colours.\n\n430.\n\nThey appear from various causes on the surface of a colourless body,\noriginally, without communication, die or immersion (βαφή); and we now\nproceed to trace them, from their faintest indication to their most\npermanent state, through the different conditions of their appearance,\nwhich for easier survey we here at once summarily state.\n\n431.\n\nFirst condition.--The contact of two smooth surfaces of hard\ntransparent bodies.\n\nFirst case: if masses or plates of glass, or if lenses are pressed\nagainst each other.\n\nSecond case: if a crack takes place in a solid mass of glass, chrystal,\nor ice.\n\nThird case: if lamellæ of transparent stones become separated.\n\nSecond condition.--If a surface of glass or a polished stone is\nbreathed upon.\n\nThird condition.--The combination of the two last; first, breathing on\nthe glass, then placing another plate of glass upon it, thus exciting\nthe colours by pressure; then removing the upper glass, upon which the\ncolours begin to fade and vanish with the breath.\n\nFourth condition.--Bubbles of various liquids, soap, chocolate, beer,\nwine, fine glass bubbles.\n\nFifth condition.--Very fine pellicles and lamellæ, produced by the\ndecomposition of minerals and metals. The pellicles of lime, the\nsurface of stagnant water, especially if impregnated with iron, and\nagain pellicles of oil on water, especially of varnish on aqua fortis.\n\nSixth condition.--If metals are heated; the operation of imparting\ntints to steel and other metals.\n\nSeventh condition.--If the surface of glass is beginning to decompose.\n\n432.\n\nFirst condition, first case. If two convex glasses, or a convex and\nplane glass, or, best of all, a convex and concave glass come in\ncontact, concentric coloured circles appear. The phenomenon exhibits\nitself immediately on the slightest pressure, and may then be gradually\ncarried through various successive states. We will describe the\ncomplete appearance at once, as we shall then be better enabled to\nfollow the different states through which it passes.\n\n433.\n\nThe centre is colourless; where the glasses are, so to speak, united\nin one by the strongest pressure, a dark grey point appears with a\nsilver white space round it: then follow, in decreasing distances,\nvarious insulated rings, all consisting of three colours, which are\nin immediate contact with each other. Each of these rings, of which\nperhaps three or four might be counted, is yellow on the inner side,\nblue on the outer, and red in the centre. Between two rings there\nappears a silver white interval. The rings which are farthest from the\ncentre are always nearer together: they are composed of red and green\nwithout a perceptible white space between them.\n\n434.\n\nWe will now observe the appearances in their gradual formation,\nbeginning from the slightest pressure.\n\n435.\n\nOn the slightest pressure the centre itself appears of a green colour.\nThen follow as far as the concentric circles extend, red and green\nrings. They are wide, accordingly, and no trace of a silver white\nspace is to be seen between them. The green is produced by the blue of\nan imperfectly developed circle, mixing with the yellow of the first\ncircle. All the remaining circles are, in this slight contact, broad;\ntheir yellow and blue edges mix together, thus producing a beautiful\ngreen. The red, however, of each circle, remains pure and untouched;\nhence the whole series is composed of these two colours.\n\n436.\n\nA somewhat stronger pressure separates the first circle by a slight\ninterval from the imperfectly developed one: it is thus detached, and\nmay be said to appear in a complete state. The centre is now a blue\npoint; for the yellow of the first circle is now separated from this\ncentral point by a silver white space. From the centre of the blue a\nred appears, which is thus, in all cases, bounded on the outside by\nits blue edge. The second and third rings from the centre are quite\ndetached. Where deviations from this order present themselves, the\nobserver will be enabled to account for them, from what has been or\nremains to be stated.\n\n437.\n\nOn a stronger pressure the centre becomes yellow; this yellow is\nsurrounded by a red and blue edge: at last, the yellow also retires\nfrom the centre; the innermost circle is formed and is bounded with\nyellow. The whole centre itself now appears silver white, till at last,\non the strongest pressure, the dark point appears, and the phenomenon,\nas described at first, is complete.\n\n438.\n\nThe relative size of the concentric circles and their intervals depends\non the form of the glasses which are pressed together.\n\n439.\n\nWe remarked above, that the coloured centre is, in fact, an undeveloped\ncircle. It is, however, often found, on the slightest pressure, that\nseveral undeveloped circles exist there, as it were, in the germ; these\ncan be successively developed before the eye of the observer.\n\n440.\n\nThe regularity of these rings is owing to the form of the convex\nglasses, and the diameter of the coloured appearance depends on the\ngreater or lesser section of a circle on which a lens is polished. We\neasily conclude from this, that by pressing plane glasses together,\nirregular appearances only will be produced; the colours, in fact,\nundulate like watered silks, and spread from the point of pressure in\nall directions. Yet, the phenomenon as thus exhibited is much more\nsplendid than in the former instance, and cannot fail to strike every\nspectator. If we make the experiment in this mode, we shall distinctly\nsee, as in the other case, that, on a slight pressure, the green and\nred waves appear; on a stronger, stripes of blue, red, and yellow,\nbecome detached. At first, the outer sides of these stripes touch; on\nincreased pressure they are separated by a silver white space.\n\n441.\n\nBefore we proceed to a further description of this phenomenon, we may\npoint out the most convenient mode of exhibiting it. Place a large\nconvex glass on a table near the window; upon this glass lay a plate\nof well-polished mirror-glass, about the size of a playing-card, and\nthe mere weight of the plate will press sufficiently to produce one\nor other of the phenomena above described. So, also, by the different\nweight of plates of glass, by other accidental circumstances, for\ninstance, by slipping the plate on the side of the convex glass where\nthe pressure cannot be so strong as in the centre, all the gradations\nabove described can be produced in succession.\n\n442.\n\nIn order to observe the phenomenon it is necessary to look obliquely\non the surface where it appears. But, above all, it is to be remarked\nthat by stooping still more, and looking at the appearance under a more\nacute angle, the circles not only grow larger but other circles are\ndeveloped from the centre, of which no trace is to be discovered when\nwe look perpendicularly, even through the strongest magnifiers.\n\n443.\n\nIn order to exhibit the phenomenon in its greatest beauty, the utmost\nattention should be paid to the cleanness of the glasses. If the\nexperiment is made with plate-glass adapted for mirrors, the glass\nshould be handled with gloves. The inner surfaces, which must come in\ncontact with the utmost nicety, may be most conveniently cleaned before\nthe experiment, and the outer surfaces should be kept clean while the\npressure is increased.\n\n444.\n\nFrom what has been said it will be seen that an exact contact of two\nsmooth surfaces is necessary. Polished glasses are best adapted for the\npurpose. Plates of glass exhibit the most brilliant colours when they\nfit closely together, and for this reason the phenomenon will increase\nin beauty if exhibited under an air-pump, by exhausting the air.\n\n445.\n\nThe appearance of the coloured rings may be produced in the greatest\nperfection by placing a convex and concave glass together which have\nbeen ground on similar segments of circles. I have never seen the\neffect more brilliant than with the object-glass of an achromatic\ntelescope, in which the crown-glass and flint-glass were necessarily\nin the closest contact.\n\n446.\n\nA remarkable appearance takes place when dissimilar surfaces are\npressed together; for example, a polished crystal and a plate of\nglass. The appearance does not at all exhibit itself in large flowing\nwaves, as in the combination of glass with glass, but it is small and\nangular, and, as it were, disjointed: thus it appears that the surface\nof the polished crystal, which consists of infinitely small sections of\nlamellæ, does not come so uninterruptedly in contact with the glass as\nanother glass-plate would.\n\n447.\n\nThe appearance of colour vanishes on the strongest pressure, which so\nintimately unites the two surfaces that they appear to make but one\nsubstance. It is this which occasions the dark centre, because the\npressed lens no longer reflects any light from this point, for the\nvery same point, when seen against the light, is perfectly clear and\ntransparent. On relaxing the pressure, the colours, in like manner,\ngradually diminish, and disappear entirely when the surfaces are\nseparated.\n\n448.\n\nThese same appearances occur in two similar cases. If entirely\ntransparent masses become partially separated, the surfaces of their\nparts being still sufficiently in contact, we see the same circles and\nwaves more or less. They may be produced in great beauty by plunging a\nhot mass of glass in water; the different fissures and cracks enabling\nus to observe the colours in various forms. Nature often exhibits the\nsame phenomena in split rock crystals.\n\n449.\n\nThis appearance, again, frequently displays itself in the mineral world\nin those kinds of stone which by nature have a tendency to exfoliate.\nThese original lamellæ are, it is true, so intimately united, that\nstones of this kind appear altogether transparent and colourless, yet,\nthe internal layers become separated, from various accidental causes,\nwithout altogether destroying the contact: thus the appearance, which\nis now familiar to us by the foregoing description, often occurs in\nnature, particularly in calcareous spars; the specularis, adularia, and\nother minerals of similar structure. Hence it shows an ignorance of the\nproximate causes of an appearance so often accidentally produced, to\nconsider it so important in mineralogy, and to attach especial value to\nthe specimens exhibiting it.\n\n450.\n\nWe have yet to speak of the very remarkable inversion of this\nappearance, as related by men of science. If, namely, instead of\nlooking at the colours by a reflected light, we examine them by a\ntransmitted light, the opposite colours are said to appear, and in\na mode corresponding with that which we have before described as\nphysiological; the colours evoking each other. Instead of blue, we\nshould thus see red-yellow; instead of red, green, &c., and _vice\nversâ_. We reserve experiments in detail, the rather as we have\nourselves still some doubts on this point.\n\n451.\n\nIf we were now called upon to give some general explanation of these\nepoptical colours, as they appear under the first condition, and to\nshow their connexion with the previously detailed physical phenomena,\nwe might proceed to do so as follows:--\n\n452.\n\nThe glasses employed for the experiments are to be regarded as the\nutmost possible practical approach to transparence. By the intimate\ncontact, however, occasioned by the pressure applied to them, their\nsurfaces, we are persuaded, immediately become in a very slight\ndegree dimmed. Within this semi-transparence the colours immediately\nappear, and every circle comprehends the whole scale; for when the two\nopposites, yellow and blue, are united by their red extremities, pure\nred appears: the green, on the other hand, as in prismatic experiments,\nwhen yellow and blue touch.\n\n453.\n\nWe have already repeatedly found that where colour exists at all, the\nwhole scale is soon called into existence; a similar principle may be\nsaid to lurk in the nature of every physical phenomenon; it already\nfollows, from the idea of polar opposition, from which an elementary\nunity or completeness results.\n\n454.\n\nThe fact that a colour exhibited by transmitted light is different\nfrom that displayed by reflected light, reminds us of those dioptrical\ncolours of the first class which we found were produced precisely in\nthe same way through semi-opacity. That here, too, a diminution of\ntransparency exists there can scarcely be a doubt; for the adhesion\nof the perfectly smooth plates of glass (an adhesion so strong that\nthey remain hanging to each other) produces a degree of union which\ndeprives each of the two surfaces, in some degree, of its smoothness\nand transparence. The fullest proof may, however, be found in the\nfact that in the centre, where the lens is most strongly pressed on\nthe other glass, and where a perfect union is accomplished, a complete\ntransparence takes place, in which we no longer perceive any colour.\nAll this may be hereafter confirmed in a recapitulation of the whole.\n\n455.\n\nSecond condition.--If after breathing on a plate of glass, the breath\nis merely wiped away with the finger, and if we then again immediately\nbreathe on the glass, we see very vivid colours gliding through each\nother; these, as the moisture evaporates, change their place, and at\nlast vanish altogether. If this operation is repeated, the colours are\nmore vivid and beautiful, and remain longer than they did the first\ntime.\n\n456.\n\nQuickly as this appearance passes, and confused as it appears to be, I\nhave yet remarked the following effects:--At first all the principal\ncolours appear with their combinations; on breathing more strongly, the\nappearance may be perceived in some order. In this succession it may be\nremarked, that when the breath in evaporating becomes contracted from\nall sides towards the centre, the blue colour vanishes last.\n\n457.\n\nThe phenomenon appears most readily between the minute lines, which the\naction of passing the fingers leaves on the clear surface; a somewhat\nrough state of the surface of the glass is otherwise requisite. On\nsome glass the appearance may be produced by merely breathing; in\nother cases the wiping with the fingers is necessary: I have even met\nwith polished mirror-glasses, one side of which immediately showed the\ncolours vividly; the other not. To judge from some remaining pieces,\nthe former was originally the front of the glass, the latter the side\nwhich was covered with quicksilver.\n\n458.\n\nThese experiments may be best made in cold weather, because the glass\nmay be more quickly and distinctly breathed upon, and the breath\nevaporates more suddenly. In severe frost the phenomenon may be\nobserved on a large scale while travelling in a carriage; the glasses\nbeing well cleaned, and all closed. The breath of the persons within is\nvery gently diffused over the glass, and immediately produces the most\nvivid play of colours. How far they may present a regular succession I\nhave not been able to remark; but they appear particularly vivid when\nthey have a dark object as a background. This alternation of colours\ndoes not, however, last long; for as soon as the breath gathers in\ndrops, or freezes to points of ice, the appearance is at once at an end.\n\n459.\n\nThird condition.--The two foregoing experiments of the pressure and\nbreathing may be united; namely, by breathing on a plate of glass, and\nimmediately after pressing the other upon it. The colours then appear\nas in the case of two glasses unbreathed upon, with this difference,\nthat the moisture occasions here and there an interruption of the\nundulations. On pushing one glass away from the other the moisture\nappears iridescent as it evaporates.\n\n460.\n\nIt might, however, be asserted that this combined experiment exhibits\nno more than each single experiment; for it appears the colours excited\nby pressure disappear in proportion as the glasses are less in contact,\nand the moisture then evaporates with its own colours.\n\n461.\n\nFourth condition.--Iridescent appearances are observable in almost all\nbubbles; soap-bubbles are the most commonly known, and the effect in\nquestion is thus exhibited in the easiest mode; but it may be observed\nin wine, beer, in pure spirit, and again, especially, in the froth of\nchocolate.\n\n462.\n\nAs in the above cases we required an infinitely narrow space between\ntwo surfaces which are in contact, so we can consider the pellicle\nof the soap-bubble as an infinitely thin lamina between two elastic\nbodies; for the appearance in fact takes place between the air within,\nwhich distends the bubble, and the atmospheric air.\n\n463.\n\nThe bubble when first produced is colourless; then coloured stripes,\nlike those in marble paper, begin to appear: these at length spread\nover the whole surface, or rather are driven round it as it is\ndistended.\n\n464.\n\nIn a single bubble, suffered to hang from the straw or tube, the\nappearance of colour is difficult to observe, for the quick rotation\nprevents any accurate observation, and all the colours seem to mix\ntogether; yet we can perceive that the colours begin at the orifice of\nthe tube. The solution itself may, however, be blown into carefully,\nso that only one bubble shall appear. This remains white (colourless)\nif not much agitated; but if the solution is not too watery, circles\nappear round the perpendicular axis of the bubble; these being near\neach other, are commonly composed alternately of green and red. Lastly,\nseveral bubbles may be produced together by the same means; in this\ncase the colours appear on the sides where two bubbles have pressed\neach other flat.\n\n465.\n\nThe bubbles of chocolate-froth may perhaps be even more conveniently\nobserved than those of soap; though smaller, they remain longer. In\nthese, owing to the heat, an impulse, a movement, is produced and\nsustained, which appears necessary to the development and succession of\nthe appearances.\n\n466.\n\nIf the bubble is small, or shut in between others, coloured lines\nchase each other over the surface, resembling marbled paper; all the\ncolours of the scale are seen to pass through each other; the pure, the\naugmented, the combined, all distinctly clear and beautiful. In small\nbubbles the appearance lasts for a considerable time.\n\n467.\n\nIf the bubble is larger, or if it becomes by degrees detached, owing\nto the bursting of others near, we perceive that this impulsion and\nattraction of the colours has, as it were, an end in view; for on\nthe highest point of the bubble we see a small circle appear, which\nis yellow in the centre; the other remaining coloured lines move\nconstantly round this with a vermicular action.\n\n468.\n\nIn a short time the circle enlarges and sinks downwards on all sides;\nin the centre the yellow remains; below and on the outside it becomes\nred, and soon blue; below this again appears a new circle of the\nsame series of colours: if they approximate sufficiently, a green is\nproduced by the union of the border-colours.\n\n469.\n\nWhen I could count three such leading circles, the centre was\ncolourless, and this space became by degrees larger as the circles sank\nlower, till at last the bubble burst.\n\n470.\n\nFifth condition.--Very delicate pellicles may be formed in various\nways: on these films we discover a very lively play of colours, either\nin the usual order, or more confusedly passing through each other. The\nwater in which lime has been slaked soon skims over with a coloured\npellicle: the same happens on the surface of stagnant water, especially\nif impregnated with iron. The lamellæ of the fine tartar which adheres\nto bottles, especially in red French wine, exhibit the most brilliant\ncolours, on being exposed to the light, if carefully detached. Drops of\noil on water, brandy, and other fluids, produce also similar circles\nand brilliant effects: but the most beautiful experiment that can be\nmade is the following:--Let aqua fortis, not too strong, be poured into\na flat saucer, and then with a brush drop on it some of the varnish\nused by engravers to cover certain portions during the process of\nbiting their plates. After quick commotion there presently appears a\nfilm which spreads itself out in circles, and immediately produces the\nmost vivid appearances of colour.\n\n471.\n\nSixth condition.--When metals are heated, colours rapidly succeeding\neach other appear on the surface: these colours can, however, be\narrested at will.\n\n472.\n\nIf a piece of polished steel is heated, it will, at a certain degree\nof warmth, be overspread with yellow. If taken suddenly away from the\nfire, this yellow remains.\n\n473.\n\nAs the steel becomes hotter, the yellow appears darker, intenser, and\npresently passes into red. This is difficult to arrest, for it hastens\nvery quickly to bright blue.\n\n474.\n\nThis beautiful blue is to be arrested if the steel is suddenly taken\nout of the heat and buried in ashes. The blue steel works are produced\nin this way. If, again, the steel is held longer over the fire, it soon\nbecomes a light blue, and so it remains.\n\n475.\n\nThese colours pass like a breath over the plate of steel; each seems\nto fly before the other, but, in reality, each successive hue is\nconstantly developed from the preceding one.\n\n476.\n\nIf we hold a penknife in the flame of a light, a coloured stripe will\nappear across the blade. The portion of the stripe which was nearest to\nthe flame is light blue; this melts into blue-red; the red is in the\ncentre; then follow yellow-red and yellow.\n\n477.\n\nThis phenomenon is deducible from the preceding ones; for the portion\nof the blade next the handle is less heated than the end which is in\nthe flame, and thus all the colours which in other cases exhibited\nthemselves in succession, must here appear at once, and may thus be\npermanently preserved.\n\n478.\n\nRobert Boyle gives this succession of colours as follows:--\"A florido\nflavo ad flavum saturum et rubescentem (quem artifices sanguineum\nvocant) inde ad languidum, postea ad saturiorem cyaneum.\" This would be\nquite correct if the words \"languidus\" and \"saturior\" were to change\nplaces. How far the observation is correct, that the different colours\nhave a relation to the degree of temper which the metal afterwards\nacquires, we leave to others to decide. The colours are here only\nindications of the different degrees of heat.--Note R.\n\n479.\n\nWhen lead is calcined, the surface is first greyish. This greyish\npowder, with greater heat, becomes yellow, and then orange. Silver,\ntoo, exhibits colours when heated; the fracture of silver in the\nprocess of refining belongs to the same class of examples. When\nmetallic glasses melt, colours in like manner appear on the surface.\n\n480.\n\nSeventh condition.--When the surface of glass becomes decomposed. The\naccidental opacity (blindwerden) of glass has been already noticed: the\nterm (blindwerden) is employed to denote that the surface of the glass\nis so affected as to appear dim to us.\n\n481.\n\nWhite glass becomes \"blind\" soonest; cast, and afterwards polished\nglass is also liable to be so affected; the bluish less, the green\nleast.\n\n482.\n\nOf the two sides of a plate of glass one is called the mirror side;\nit is that which in the oven lies uppermost, on which one may observe\nroundish elevations: it is smoother than the other, which is undermost\nin the oven, and on which scratches may be sometimes observed. On this\naccount the mirror side is placed facing the interior of rooms, because\nit is less affected by the moisture adhering to it from within, than\nthe other would be, and the glass is thus less liable to become \"blind.\"\n\n483.\n\nThis half-opacity or dimness of the glass assumes by degrees an\nappearance of colour which may become very vivid, and in which perhaps\na certain succession, or otherwise regular order, might be discovered.\n\n484.\n\nHaving thus traced the physical colours from their simplest effects to\nthe present instances, where these fleeting appearances are found to\nbe fixed in bodies, we are, in fact, arrived at the point where the\nchemical colours begin; nay, we have in some sort already passed those\nlimits; a circumstance which may excite a favourable prejudice for the\nconsistency of our statement. By way of conclusion to this part of our\ninquiry, we subjoin a general observation, which may not be without its\nbearing on the common connecting principle of the phenomena that have\nbeen adduced.\n\n485.\n\nThe colouring of steel and the appearances analogous to it, might\nperhaps be easily deduced from the doctrine of the semi-opaque mediums.\nPolished steel reflects light powerfully: we may consider the colour\nproduced by the heat as a slight degree of dimness: hence a bright\nyellow must immediately appear; this, as the dimness increases, must\nstill appear deeper, more condensed, and redder, and at last pure and\nruby-red. The colour has now reached the extreme point of depth, and\nif we suppose the same degree of semi-opacity still to continue, the\ndimness would now spread itself over a dark ground, first producing a\nviolet, then a dark-blue, and at last a light-blue, and thus complete\nthe series of the appearances.\n\nWe will not assert that this mode of explanation will suffice in\nall cases; our object is rather to point out the road by which the\nall-comprehensive formula, the very key of the enigma, may be at last\ndiscovered.--Note S.\n\n\n\n\n## PART III.\n\n\n\n## CHEMICAL COLOURS.\n\n\n\n486.\n\nWe give this denomination to colours which we can produce, and more\nor less fix, in certain bodies; which we can render more intense,\nwhich we can again take away and communicate to other bodies, and to\nwhich, therefore, we ascribe a certain permanency: duration is their\nprevailing characteristic.\n\n487.\n\nIn this view the chemical colours were formerly distinguished with\nvarious epithets; they were called _colores proprii, corporei,\nmateriales, veri, permanentes, fixi_.\n\n488.\n\nIn the preceding chapter we observed how the fluctuating and transient\nnature of the physical colours becomes gradually fixed, thus forming\nthe natural transition to our present subject.\n\n489.\n\nColour becomes fixed in bodies more or less permanently; superficially,\nor thoroughly.\n\n490.\n\nAll bodies are susceptible of colour; it can either be excited,\nrendered intense, and gradually fixed in them, or at least communicated\nto them.\n\n\n\n\n## XXXIV.\n\n\n\n## CHEMICAL CONTRAST.\n\n\n\n491.\n\nIn the examination of coloured appearances we had occasion everywhere\nto take notice of a principle of contrast: so again, in approaching the\nprecincts of chemistry, we find a chemical contrast of a remarkable\nnature. We speak here, with reference to our present purpose, only of\nthat which is comprehended under the general names of acid and alkali.\n\n492.\n\nWe characterised the chromatic contrast, in conformity with all other\nphysical contrasts as a _more_ and _less_; ascribing the _plus_ to\nthe yellow side, the _minus_ to the blue; and we now find that these\ntwo divisions correspond with the chemical contrasts. The yellow and\nyellow-red affect the acids, the blue and blue-red the alkalis; thus\nthe phenomena of chemical colours, although still necessarily mixed\nup with other considerations, admit of being traced with sufficient\nsimplicity.\n\n493.\n\nThe principal phenomena in chemical colours are produced by the\noxydation of metals, and it will be seen how important this\nconsideration is at the outset. Other facts which come into the\naccount, and which are worthy of attention, will be examined under\nseparate heads; in doing this we, however, expressly state that we only\npropose to offer some preparatory suggestions to the chemist in a very\ngeneral way, without entering into the nicer chemical problems and\nquestions, or presuming to decide on them. Our object is only to give a\nsketch of the mode in which, according to our conviction, the chemical\ntheory of colours may be connected with general physics.\n\n\n\n\n## XXXV.\n\n\n\n## WHITE.\n\n\n\n494.\n\nIn treating of the dioptrical colours of the first class (155) we\nhave already in some degree anticipated this subject. Transparent\nsubstances may be said to be in the highest class of inorganic matter.\nWith these, colourless semi-transparence is closely connected, and\nwhite may be considered the last opaque degree of this.\n\n495.\n\nPure water crystallised to snow appears white, for the transparence of\nthe separate parts makes no transparent whole. Various crystallised\nsalts, when deprived to a certain extent of moisture, appear as a white\npowder. The accidentally opaque state of a pure transparent substance\nmight be called white; thus pounded glass appears as a white powder.\nThe cessation of a combining power, and the exhibition of the atomic\nquality of the substance might at the same time be taken into the\naccount.\n\n496.\n\nThe known undecomposed earths are, in their pure state, all white.\nThey pass to a state of transparence by natural crystallization. Silex\nbecomes rock-crystal; argile, mica; magnesia, talc; calcareous earth\nand barytes appear transparent in various spars.--Note T.\n\n497.\n\nAs in the colouring of mineral bodies the metallic oxydes will often\ninvite our attention, we observe, in conclusion, that metals, when\nslightly oxydated, at first appear white, as lead is converted to white\nlead by vegetable acid.\n\n\n\n\n## XXXVI.\n\n\n\n## BLACK.\n\n\n\n498.\n\nBlack is not exhibited in so elementary a state as white. We meet\nwith it in the vegetable kingdom in semi-combustion; and charcoal, a\nsubstance especially worthy of attention on other accounts, exhibits\na black colour. Again, if woods--for example, boards, owing to the\naction of light, air, and moisture, are deprived in part of their\ncombustibility, there appears first the grey then the black colour. So\nagain, we can convert even portions of animal substance to charcoal by\nsemi-combustion.\n\n499.\n\nIn the same manner we often find that a sub-oxydation takes place\nin metals when the black colour is to be produced. Various metals,\nparticularly iron, become black by slight oxydation, by vinegar, by\nmild acid fermentations; for example, a decoction of rice, &c.\n\n500.\n\nAgain, it may be inferred that a de-oxydation may produce black. This\noccurs in the preparation of ink, which becomes yellow by the solution\nof iron in strong sulphuric acid, but when partly de-oxydised by the\ninfusion of gall-nuts, appears black.\n\n\n\n\n## XXXVII.\n\n\n\n## FIRST EXCITATION OF COLOUR.\n\n\n\n501.\n\nIn the division of physical colours, where semi-transparent mediums\nwere considered, we saw colours antecedently to white and black. In the\npresent case we assume a white and black already produced and fixed;\nand the question is, how colour can be excited in them?\n\n502.\n\nHere, too, we can say, white that becomes darkened or dimmed inclines\nto yellow; black, as it becomes lighter, inclines to blue.--Note U.\n\n503.\n\nYellow appears on the active (plus) side, immediately in the light, the\nbright, the white. All white surfaces easily assume a yellow tinge;\npaper, linen, wool, silk, wax: transparent fluids again, which have\na tendency to combustion, easily become yellow; in other words they\neasily pass into a very slight state of semi-transparence.\n\n504.\n\nSo again the excitement on the passive side, the tendency to obscure,\ndark, black, is immediately accompanied with blue, or rather with a\nreddish-blue. Iron dissolved in sulphuric acid, and much diluted with\nwater, if held to the light in a glass, exhibits a beautiful violet\ncolour as soon as a few drops only of the infusion of gall-nuts are\nadded. This colour presents the peculiar hues of the dark topaz, the\n_orphninon_ of a burnt-red, as the ancients expressed it.\n\n505.\n\nWhether any colour can be excited in the pure earths by the chemical\noperations of nature and art, without the admixture of metallic oxydes,\nis an important question, generally, indeed, answered in the negative.\nIt is perhaps connected with the question--to what extent changes may\nbe produced in the earths through oxydation?\n\n506.\n\nUndoubtedly the negation of the above question is confirmed by the\ncircumstance that wherever mineral colours are found, some trace of\nmetal, especially of iron, shows itself; we are thus naturally led\nto consider how easily iron becomes oxydised, how easily the oxyde\nof iron assumes different colours, how infinitely divisible it is,\nand how quickly it communicates its colour. It were to be wished,\nnotwithstanding, that new experiments could be made in regard to the\nabove point, so as either to confirm or remove any doubt.\n\n507.\n\nHowever this may be, the susceptibility of the earths with regard\nto colours already existing is very great; aluminous earth is thus\nparticularly distinguished.\n\n508.\n\nIn proceeding to consider the metals, which in the inorganic world\nhave the almost exclusive prerogative of appearing coloured, we find\nthat, in their pure, independent, natural state, they are already\ndistinguished from the pure earths by a tendency to some one colour or\nother.\n\n509.\n\nWhile silver approximates most to pure white,--nay, really represents\npure white, heightened by metallic splendour,--steel, tin, lead, and so\nforth, incline towards pale blue-grey; gold, on the other hand, deepens\nto pure yellow, copper approaches a red hue, which, under certain\ncircumstances, increases almost to bright red, but which again returns\nto a yellow golden colour when combined with zinc.\n\n510.\n\nBut if metals in their pure state have so specific a determination\ntowards this or that exhibition of colour, they are, through the effect\nof oxydation, in some degree reduced to a common character; for the\nelementary colours now come forth in their purity, and although this\nor that metal appears to have a particular tendency to this or that\ncolour, we find some that can go through the whole circle of hues,\nothers, that are capable of exhibiting more than one colour; tin,\nhowever, is distinguished by its comparative inaptitude to become\ncoloured. We propose to give a table hereafter, showing how far the\ndifferent metals can be more or less made to exhibit the different\ncolours.\n\n511.\n\nWhen the clean, smooth surface of a pure metal, on being heated,\nbecomes overspread with a mantling colour, which passes through a\nseries of appearances as the heat increases, this, we are persuaded,\nindicates the aptitude of the metal to pass through the whole range of\ncolours. We find this phenomenon most beautifully exhibited in polished\nsteel; but silver, copper, brass, lead, and tin, easily present similar\nappearances. A superficial oxydation is probably here taking place,\nas may be inferred from the effects of the operation when continued,\nespecially in the more easily oxydizable metals.\n\n512.\n\nThe same conclusion may be drawn from the fact that iron is more\neasily oxydizable by acid liquids when it is red hot, for in this\ncase the two effects concur with each other. We observe, again, that\nsteel, accordingly as it is hardened in different stages of its\ncolorification, may exhibit a difference of elasticity: this is quite\nnatural, for the various appearances of colour indicate various degrees\nof heat.[1]\n\n513.\n\nIf we look beyond this superficial mantling, this pellicle of colour,\nwe observe that as metals are oxydized throughout their masses, white\nor black appears with the first degree of heat, as may be seen in white\nlead, iron, and quicksilver.\n\n514.\n\nIf we examine further, and look for the actual exhibition of colour,\nwe find it most frequently on the _plus_ side. The mantling, so often\nmentioned, of smooth metallic surfaces begins with yellow. Iron\npasses presently into yellow ochre, lead from white lead to massicot,\nquicksilver from æthiops to yellow turbith. The solutions of gold and\nplatinum in acids are yellow.\n\n515.\n\nThe exhibitions on the _minus_ side are less frequent. Copper slightly\noxydized appears blue. In the preparation of Prussian-blue, alkalis are\nemployed.\n\n516.\n\nGenerally, however, these appearances of colour are of so mutable a\nnature that chemists look upon them as deceptive tests, at least in the\nnicer gradations. For ourselves, as we can only treat of these matters\nin a general way, we merely observe that the appearances of colour in\nmetals may be classed according to their origin, manifold appearance,\nand cessation, as various results of oxydation, hyper-oxydation,\nab-oxydation, and de-oxydation.[2]\n\n\n[1] See par. 478.\n\n[2] As these terms are afterwards referred to (par. 525), it was\nnecessary to preserve them.\n\n\n\n\n## XXXVIII.\n\n\n\nAUGMENTATION OF COLOUR.[1]\n\n\n517.\n\nThe augmentation of colour exhibits itself as a condensation, a\nfulness, a darkening of the hue. We have before seen, in treating of\ncolourless mediums, that by increasing the degree of opacity in the\nmedium, we can deepen a bright object from the lightest yellow to the\nintensest ruby-red. Blue, on the other hand, increases to the most\nbeautiful violet, if we rarefy and diminish a semi-opaque medium,\nitself lighted, but through which we see darkness (150, 151).\n\n518.\n\nIf the colour is positive, a similar colour appears in the intenser\nstate. Thus if we fill a white porcelain cup with a pure yellow\nliquor, the fluid will appear to become gradually redder towards the\nbottom, and at last appears orange. If we pour a pure blue solution\ninto another cup, the upper portion will exhibit a sky-blue, that\ntowards the bottom, a beautiful violet. If the cup is placed in the\nsun, the shadowed side, even of the upper portion, is already violet.\nIf we throw a shadow with the hand, or any other substance, over the\nillumined portion, the shadow in like manner appears reddish.\n\n519.\n\nThis is one of the most important appearances connected with the\ndoctrine of colours, for we here manifestly find that a difference of\nquantity produces a corresponding qualified impression on our senses.\nIn speaking of the last class of epoptical colours (452, 485), we\nstated our conjecture that the colouring of steel might perhaps be\ntraced to the doctrine of the semi-transparent mediums, and we would\nhere again recall this to the reader's recollection.\n\n520.\n\nAll chemical augmentation of colour, again, is the immediate\nconsequence of continued excitation. The augmentation advances\nconstantly and unremittingly, and it is to be observed that the\nincrease of intenseness is most common on the _plus_ side. Yellow iron\nochre increases, as well by fire as by other operations, to a very\nstrong red: massicot is increased to red lead, turbith to vermilion,\nwhich last attains a very high degree of the yellow-red. An intimate\nsaturation of the metal by the acid, and its separation to infinity,\ntake place together with the above effects.\n\n521.\n\nThe augmentation on the _minus_ side is less frequent; but we observe\nthat the more pure and condensed the Prussian-blue or cobalt glass is\nprepared, the more readily it assumes a reddish hue and inclines to the\nviolet.\n\n522.\n\nThe French have a happy expression for the less perceptible tendency of\nyellow and blue towards red: they say the colour has \"un œil de rouge,\"\nwhich we might perhaps express by a reddish glance (einen röthlichen\nblick).\n\n\n[1] Steigerung, literally _gradual ascent_. See the note to par. 523.\n\n\n\n\n## XXXIX.\n\n\n\nCULMINATION[1]\n\n\n523.\n\nThis is the consequence of still progressing augmentation. Red, in\nwhich neither yellow nor blue is to be detected, here constitutes the\nacme.\n\n524.\n\nIf we wish to select a striking example of a culmination on the _plus_\nside, we again find it in the coloured steel, which attains the bright\nred acme, and can be arrested at this point.\n\n525.\n\nWere we here to employ the terminology before proposed, we should\nsay that the first oxydation produces yellow, the hyper-oxydation\nyellow-red; that here a kind of maximum exists, and that then an\nab-oxydation, and lastly a de-oxydation takes place.\n\n526.\n\nHigh degrees of oxydation produce a bright red. Gold in solution,\nprecipitated by a solution of tin, appears bright red: oxyde of\narsenic, in combination, with sulphur, produces a ruby colour.\n\n527.\n\nHow far, however, a kind of sub-oxydation may co-operate in some\nculminations, is matter for inquiry; for an influence of alkalis on\nyellow-red also appears to produce the culmination; the colour reaching\nthe acme by being forced towards the _minus_ side.\n\n528.\n\nThe Dutch prepare a colour known by the name of vermilion, from the\nbest Hungarian cinnabar, which exhibits the brightest yellow-red. This\nvermilion is still only a cinnabar, which, however, approximates the\npure red, and it may be conjectured that alkalis are used to bring it\nnearer to the culminating point.\n\n529.\n\nVegetable juices, treated in this way, offer very striking examples of\nthe above effects. The colouring-matter of turmeric, annotto, dyer's\nsaffron,[2] and other vegetables, being extracted with spirits of wine,\nexhibits tints of yellow, yellow-red, and hyacinth-red; these, by the\nadmixture of alkalis, pass to the culminating point, and even beyond it\nto blue-red.\n\n530.\n\nNo instance of a culmination on the _minus_ side has come to my\nknowledge in the mineral and vegetable kingdoms. In the animal\nkingdom the juice of the murex is remarkable; of its augmentation and\nculmination on the _minus_ side, we shall hereafter have occasion to\nspeak.\n\n\n[1] _Culmination_, the original word. It might have been rendered\n_maximum of colour_, but as the author supposes an _ascent_ through\nyellow and blue to red, his meaning is better expressed by his own term.\n\n[2] Curcuma, Bixa Orellana, Carthamus Tinctorius.\n\n\n\n\nXL.\n\n\n## FLUCTUATION.\n\n\n\n531.\n\nThe mutability of colour is so great, that even those pigments, which\nmay have been considered to be defined and arrested, still admit of\nslight variations on one side or the other. This mutability is most\nremarkable near the culminating point, and is effected in a very\nstriking manner by the alternate employment of acids and alkalis.\n\n532.\n\nTo express this appearance in dyeing, the French make use of the word\n\"virer,\" to turn from one side to the other; they thus very adroitly\nconvey an idea which others attempt to express by terms indicating the\ncomponent hues.\n\n533.\n\nThe effect produced with litmus is one of the most known and striking\nof this kind. This colouring substance is tendered red-blue by means of\nalkalis. The red-blue is very readily changed to red-yellow by means\nof acids, and again returns to its first state by again employing\nalkalis. The question whether a culminating point is to be discovered\nand arrested by nice experiments, is left to those who are practised\nin these operations. Dyeing, especially scarlet-dyeing, might afford a\nvariety of examples of this fluctuation.\n\n\n\n\nXLI.\n\n\n## PASSAGE THROUGH THE WHOLE SCALE.\n\n\n\n534.\n\nThe first excitation and gradual increase of colour take place more on\nthe _plus_ than on the _minus_ side. So, also, in passing through the\nwhole scale, colour exhibits itself most on the _plus_ side.\n\n535.\n\nA passage of this kind, regular and evident to the senses, from yellow\nthrough red to blue, is apparent in the colouring of steel.\n\n536.\n\nThe metals may be arrested at various points of the colorific circle by\nvarious degrees and kinds of oxydation.\n\n537.\n\nAs they also appear green, a question arises whether chemists know any\ninstance in the mineral kingdom of a constant transition from yellow,\nthrough green, to blue, and _vice versâ_. Oxyde of iron, melted with\nglass, produces first a green, and with a more powerful heat, a blue\ncolour.\n\n538.\n\nWe may here observe of green generally, that it appears, especially\nin an atomic sense, and certainly in a pure state, when we mix blue\nand yellow: but, again, an impure and dirty yellow soon gives us the\nimpression of green; yellow and black already produce green; this,\nhowever, is owing to the affinity between black and blue. An imperfect\nyellow, such as that of sulphur, gives us the impression of a greenish\nhue: thus, again, an imperfect blue appears green. The green of wine\nbottles arises, it appears, from an imperfect union of the oxyde of\niron with the glass. If we produce a more complete union by greater\nheat, a beautiful blue-glass is the result.\n\n539.\n\nFrom all this it appears that a certain chasm exists in nature between\nyellow and blue, the opposite characters of which, it is true, may be\ndone away atomically by due immixture, and, thus combined, to green;\nbut the true reconciliation between yellow and blue, it seems, only\ntakes place by means of red.\n\n540.\n\nThe process, however, which appears unattainable in inorganic\nsubstances, we shall find to be possible when we turn our attention to\norganic productions; for in these, the passage through the whole circle\nfrom yellow, through green and blue, to red, really takes place.\n\n\n\n\n## XLII.\n\n\n\n## INVERSION.\n\n\n\n541.\n\nAgain, an immediate inversion or change to the totally opposite hue, is\na very remarkable appearance which sometimes occurs; at present, we are\nmerely enabled to adduce what follows.\n\n542.\n\nThe mineral chameleon, a name which has been given to an oxyde of\nmanganese, may be considered, in its perfectly dry state, as a green\npowder. If we strew it in water, the green colour displays itself very\nbeautifully in the first moment of solution, but it changes presently\nto the bright red opposite to green, without any apparent intermediate\nstate.\n\n543.\n\nThe same occurs with the sympathetic ink, which may be considered a\nreddish liquid, but which, when dried by warmth, appears as a green\ncolour on paper.\n\n544.\n\nIn fact, this phenomenon appears to be owing to the conflict between\na dry and moist state, as has been already observed, if we are not\nmistaken, by the chemists. We may look to the improvements of time to\npoint out what may further be deduced from these phenomena, and to show\nwhat other facts they may be connected with.\n\n\n\n\n## XLIII.\n\n\n\n## FIXATION.\n\n\n\n545.\n\nMutable as we have hitherto found colour to be, even as a substance,\nyet under certain circumstances it may at last be fixed.\n\n546.\n\nThere are bodies capable of being entirely converted into colouring\nmatter: here it may be said that the colour fixes itself in its own\nsubstance, stops at a certain point, and is there defined. Such\ncolouring substances are found throughout nature; the vegetable world\naffords a great quantity of examples, among which some are particularly\ndistinguished, and may be considered as the representatives of the\nrest; such as, on the active side, madder, on the passive side, indigo.\n\n547.\n\nIn order to make these materials available in use, it is necessary\nthat the colouring quality in them should be intimately condensed, and\nthe tinging substance refined, practically speaking, to an infinite\ndivisibility. This is accomplished in various ways, and particularly by\nthe well-known means of fermentation and decomposition.\n\n548.\n\nThese colouring substances now attach themselves again to other bodies.\nThus, in the mineral kingdom they adhere to earths and metallic oxydes;\nthey unite in melting with glasses; and in this case, as the light is\ntransmitted through them, they appear in the greatest beauty, while an\neternal duration may be ascribed to them.\n\n549.\n\nThey fasten on vegetable and animal bodies with more or less power, and\nremain more or less permanently; partly owing to their nature,--as\nyellow, for instance, is more evanescent than blue,--or owing to\nthe nature of the substance on which they appear. They last less in\nvegetable than in animal substances, and even within this latter\nkingdom there are again varieties. Hemp or cotton threads, silk or\nwool, exhibit very different relations to colouring substances.\n\n550.\n\nHere comes into the account the important operation of employing\nmordants, which may be considered as the intermediate agents between\nthe colour and the recipient substance; various works on dyeing speak\nof this circumstantially. Suffice it to have alluded to processes by\nmeans of which the colour retains a permanency only to be destroyed\nwith the substance, and which may even increase in brightness and\nbeauty by use.\n\n\n\n\n## XLIV.\n\n\n\n## INTERMIXTURE, REAL.\n\n\n\n551.\n\nEvery intermixture pre-supposes a specific state of colour; and thus\nwhen we speak of intermixture, we here understand it in an atomic\nsense. We must first have before us certain bodies arrested at any\ngiven point of the colorific circle, before we can produce gradations\nby their union.\n\n552.\n\nYellow, blue, and red, may be assumed as pure elementary colours,\nalready existing; from these, violet, orange, and green, are the\nsimplest combined results.\n\n553.\n\nSome persons have taken much pains to define these intermixtures more\naccurately, by relations of number, measure, and weight, but nothing\nvery profitable has been thus accomplished.\n\n554.\n\nPainting consists, strictly speaking, in the intermixture of\nsuch specific colouring bodies and their infinite possible\ncombinations--combinations which can only be appreciated by the nicest,\nmost practised eye, and only accomplished under its influence.\n\n555.\n\nThe intimate combination of these ingredients is effected, in the first\ninstance, through the most perfect comminution of the material by means\nof grinding, washing, &c., as well as by vehicles or liquid mediums\nwhich hold together the pulverized substance, and combine organically,\nas it were, the unorganic; such are the oils, resins, &c.--Note V.\n\n556.\n\nIf all the colours are mixed together they retain their general\ncharacter as σκιερόν, and as they are no longer seen next each other,\nno completeness, no harmony, is experienced; the result is grey, which,\nlike apparent colour, always appears somewhat darker than white, and\nsomewhat lighter than black.\n\n557.\n\nThis grey may be produced in various ways. By mixing yellow and blue to\nan emerald green, and then adding pure red, till all three neutralize\neach other; or, by placing the primitive and intermediate colours next\neach other in a certain proportion, and afterwards mixing them.\n\n558.\n\nThat all the colours mixed together produce white, is an absurdity\nwhich people have credulously been accustomed to repeat for a century,\nin opposition to the evidence of their senses.\n\n559.\n\nColours when mixed together retain their original darkness. The darker\nthe colours, the darker will be the grey resulting from their union,\ntill at last this grey approaches black. The lighter the colours the\nlighter will be the grey, which at last approaches white.\n\n\n\n\nXLV.\n\n\n## INTERMIXTURE, APPARENT.\n\n\n\n560.\n\nThe intermixture, which is only apparent, naturally invites our\nattention in connexion with the foregoing; it is in many respects\nimportant, and, indeed, the intermixture which we have distinguished as\nreal, might be considered as merely apparent. For the elements of which\nthe combined colour consists are only too small to be considered as\ndistinct parts. Yellow and blue powders mingled together appear green\nto the naked eye, but through a magnifying glass we can still perceive\nyellow and blue distinct from each other. Thus yellow and blue stripes\nseen at a distance, present a green mass; the same observation is\napplicable with regard to the intermixture of other specific colours.\n\n561.\n\nIn the description of our apparatus we shall have occasion to mention\nthe wheel by means of which the apparent intermixture is produced by\nrapid movement. Various colours are arranged near each other round\nthe edge of a disk, which is made to revolve with velocity, and thus\nby having several such disks ready, every possible intermixture can\nbe presented to the eye, as well as the mixture of all colours to\ngrey, darker or lighter, according to the depth of the tints as above\nexplained.\n\n562.\n\nPhysiological colours admit, in like manner, of being mixed with\nothers. If, for example, we produce the blue shadow (65) on a light\nyellow paper, the surface will appear green. The same happens with\nregard to the other colours if the necessary preparations are attended\nto.\n\n563.\n\nIf, when the eye is impressed with visionary images that last for a\nwhile, we look on coloured surfaces, an intermixture also takes place;\nthe spectrum is determined to a new colour which is composed of the two.\n\n564.\n\nPhysical colours also admit of combination. Here might be adduced the\nexperiments in which many-coloured images are seen through the prism,\nas we have before shown in detail (258, 284).\n\n565.\n\nThose who have prosecuted these inquiries have, however, paid most\nattention to the appearances which take place when the prismatic\ncolours are thrown on coloured surfaces.\n\n566.\n\nWhat is seen under these circumstances is quite simple. In the first\nplace it must be remembered that the prismatic colours are much more\nvivid than the colours of the surface on which they are thrown.\nSecondly, we have to consider that the prismatic colours may be either\nhomogeneous or heterogeneous, with the recipient surface. In the former\ncase the surface deepens and enhances them, and is itself enhanced in\nreturn, as a coloured stone is displayed by a similarly coloured foil.\nIn the opposite case each vitiates, disturbs, and destroys the other.\n\n567.\n\nThese experiments may be repeated with coloured glasses, by causing the\nsun-light to shine through them on coloured surfaces. In every instance\nsimilar results will appear.\n\n568.\n\nThe same effect takes place when we look on coloured objects through\ncoloured glasses; the colours being thus according to the same\nconditions enhanced, subdued, or neutralized.\n\n569.\n\nIf the prismatic colours are suffered to pass through coloured glasses,\nthe appearances that take place are perfectly analogous; in these cases\nmore or less force, more or less light and dark, the clearness and\ncleanness of the glass are all to be allowed for, as they produce many\ndelicate varieties of effect: these will not escape the notice of every\naccurate observer who takes sufficient interest in the inquiry to go\nthrough the experiments.\n\n570.\n\nIt is scarcely necessary to mention that several coloured glasses, as\nwell as oiled or transparent papers, placed over each other, may be\nmade to produce and exhibit every kind of intermixture at pleasure.\n\n571.\n\nLastly, the operation of glazing in painting belongs to this kind of\nintermixture; by this means a much more refined union may be produced\nthan that arising from the mechanical, atomic mixture which is commonly\nemployed.\n\n\n\n\n## XLVI.\n\n\n\n## COMMUNICATION, ACTUAL.\n\n\n\n572.\n\nHaving now provided the colouring materials, as before shown, a further\nquestion arises how to communicate these to colourless substances:\nthe answer is of the greatest importance from the connexion of the\nobject with the ordinary wants of men, with useful purposes, and with\ncommercial and technical interests.\n\n573.\n\nHere, again, the dark quality of every colour again comes into the\naccount. From a yellow, that is very near to white, through orange,\nand the hue of minium to pure red and carmine, through all gradations\nof violet to the deepest blue which is almost identified with black,\ncolour still increases in darkness. Blue once defined, admits of\nbeing diluted, made light, united with yellow, and then, as green,\nit approaches the light side of the scale: but this is by no means\naccording to its own nature.\n\n574.\n\nIn the physiological colours we have already seen that they are less\nthan the light, inasmuch as they are a repetition of an impression\nof light, nay, at last they leave this impression quite as a dark. In\nphysical experiments the employment of semi-transparent mediums, the\neffect of semi-transparent accessory images, taught us that in such\ncases we have to do with a subdued light, with a transition to darkness.\n\n575.\n\nIn treating of the chemical origin of pigments we found that the same\neffect was produced on the very first excitement. The yellow tinge\nwhich mantles over the steel, already darkens the shining surface. In\nchanging white lead to massicot it is evident that the yellow is darker\nthan white.\n\n576.\n\nThis process is in the highest degree delicate; the growing\nintenseness, as it still increases, tinges the substance more and more\nintimately and powerfully, and thus indicates the extreme fineness, and\nthe infinite divisibility of the coloured atoms.\n\n577.\n\nThe colours which approach the dark side, and consequently, blue in\nparticular, can be made to approximate to black; in fact, a very\nperfect Prussian blue, or an indigo acted on by vitriolic acid appears\nalmost as a black.\n\n578.\n\nA remarkable appearance may be here adverted to; pigments, in their\ndeepest and most condensed state, especially those produced from\nthe vegetable kingdom, such as the indigo just mentioned, or madder\ncarried to its intensest hue, no longer show their own colour; on the\ncontrary, a decided metallic shine is seen on their surface, in which\nthe physiological compensatory colour appears.\n\n579.\n\nAll good indigo exhibits a copper-colour in its fracture, a\ncircumstance attended to, as a known characteristic, in trade. Again,\nthe indigo which has been acted on by sulphuric acid, if thickly laid\non, or suffered to dry so that neither white paper nor the porcelain\ncan appear through, exhibits a colour approaching to orange.\n\n580.\n\nThe bright red Spanish rouge, probably prepared from madder, exhibits\non its surface a perfectly green, metallic shine. If this colour, or\nthe blue before mentioned, is washed with a pencil on porcelain or\npaper, it is seen in its real state owing to the bright ground shining\nthrough.\n\n581.\n\nColoured liquids appear black when no light is transmitted through\nthem, as we may easily see in cubic tin vessels with glass bottoms.\nIn these every transparent-coloured infusion will appear black and\ncolourless if we place a black surface under them.\n\n582.\n\nIf we contrive that the image of a flame be reflected from the bottom,\nthe image will appear coloured. If we lift up the vessel and suffer the\ntransmitted light to fall on white paper under it, the colour of the\nliquid appears on the paper. Every light ground seen through such a\ncoloured medium exhibits the colour of the medium.\n\n583.\n\nThus every colour, in order to be seen, must have a light within or\nbehind it. Hence the lighter and brighter the grounds are, the more\nbrilliant the colours appear. If we pass lac-varnish over a shining\nwhite metal surface, as the so-called foils are prepared, the splendour\nof the colour is displayed by this internally reflected light as\npowerfully as in any prismatic experiment; nay, the force of the\nphysical colours is owing principally to the circumstance that light is\nalways acting with and behind them.\n\n584.\n\nLichtenberg, who of necessity followed the received theory, owing\nto the time and circumstances in which he lived, was yet too good an\nobserver, and too acute not to explain and classify, after his fashion,\nwhat was evident to his senses. He says, in the preface to Delaval,\n\"It appears to me also, on other grounds, probable, that our organ, in\norder to be impressed by a colour, must at the same time be impressed\nby all light (white).\"\n\n585.\n\nTo procure white as a ground is the chief business of the dyer. Every\ncolour may be easily communicated to colourless earths, especially\nto alum: but the dyer has especially to do with animal and vegetable\nproducts as the ground of his operations.\n\n586.\n\nEverything living tends to colour--to local, specific colour, to\neffect, to opacity--pervading the minutest atoms. Everything in which\nlife is extinct approximates to white (494), to the abstract, the\ngeneral state, to clearness[1], to transparence.\n\n587.\n\nHow this is put in practice in technical operations remains to be\nadverted to in the chapter on the privation of colour. With regard\nto the communication of colour, we have especially to bear in mind\nthat animals and vegetables, in a living state, produce colours, and\nhence their substances, if deprived of colours, can the more readily\nre-assume them.\n\n\n[1] Verklärung, literally _clarification_.\n\n\n\n\n## XLVII.\n\n\n\n## COMMUNICATION, APPARENT.\n\n\n\n588.\n\nThe communication of colours, real as well as apparent, corresponds, as\nmay easily be seen, with their intermixture: we need not, therefore,\nrepeat what has been already sufficiently entered into.\n\n589.\n\nYet we may here point out more circumstantially the importance of an\napparent communication which takes place by means of reflection. This\nphenomenon is well known, but still it is pregnant with inferences, and\nis of the greatest importance both to the investigator of nature and to\nthe painter.\n\n590.\n\nLet a surface coloured with any one of the positive colours be placed\nin the sun, and let its reflection be thrown on other colourless\nobjects. This reflection is a kind of subdued light, a half-light,\na half-shadow, which, in a subdued state, reflects the colours in\nquestion.\n\n591.\n\nIf this reflection acts on light surfaces, it is so far overpowered\nthat we can scarcely perceive the colour which accompanies it; but if\nit acts on shadowed portions, a sort of magical union takes place with\nthe σκιερῷ. Shadow is the proper element of colour, and in this case\na subdued colour approaches it, lighting up, tinging, and enlivening\nit. And thus arises an appearance, as powerful as agreeable, which may\nrender the most pleasing service to the painter who knows how to make\nuse of it. These are the types of the so-called reflexes, which were\nonly noticed late in the history of art, and which have been too seldom\nemployed in their full variety.\n\n592.\n\nThe schoolmen called these colours _colores notionales_ and\n_intentionales_, and the history of the doctrine of colours will\ngenerally show that the old inquirers already observed the phenomena\nwell enough, and knew how to distinguish them properly, although the\nwhole method of treating such subjects is very different from ours.\n\n\n\n\n## XLVIII.\n\n\n\n## EXTRACTION.\n\n\n\n593.\n\nColour may be extracted from substances, whether they possess it\nnaturally or by communication, in various ways. We have thus the power\nto remove it intentionally for a useful purpose, but, on the other\nhand, it often flies contrary to our wish.\n\n594.\n\nNot only are the elementary earths in their natural state white, but\nvegetable and animal substances can be reduced to a white state without\ndisturbing their texture. A pure white is very desirable for various\nuses, as in the instance of our preferring to use linen and cotton\nstuffs uncoloured. In like manner some silk stuffs, paper, and other\nsubstances, are the more agreeable the whiter they can be. Again,\nthe chief basis of all dyeing consists in white grounds. For these\nreasons manufacturers, aided by accident and contrivance, have devoted\nthemselves assiduously to discover means of extracting colour: infinite\nexperiments have been made in connexion with this object, and many\nimportant facts have been arrived at.\n\n595.\n\nIt is in accomplishing this entire extraction of colour that the\noperation of bleaching consists, which is very generally practised\nempirically or methodically. We will here shortly state the leading\nprinciples.\n\n596.\n\nLight is considered as one of the first means of extracting colour\nfrom substances, and not only the sun-light, but the mere powerless\nday-light: for as both lights--the direct light of the sun, as well as\nthe derived light of the sky--kindle Bologna phosphorus, so both act on\ncoloured surfaces. Whether the light attacks the colour allied to it,\nand, as it were, kindles and consumes it, thus reducing the definite\nquality to a general state, or whether some other operation, unknown\nto us, takes place, it is clear that light exercises a great power on\ncoloured surfaces, and bleaches them more or less. Here, however, the\ndifferent colours exhibit a different degree of durability; yellow,\nespecially if prepared from certain materials, is, in this case, the\nfirst to fly.\n\n597.\n\nNot only light, but air, and especially water, act strongly in\ndestroying colour. It has been even asserted that thread, well soaked\nand spread on the grass at night, bleaches better than that which is\nexposed, after soaking, to the sun-light. Thus, in this case, water\nproves to be a solving and conducting agent, removing the accidental\nquality, and restoring the substance to a general or colourless state.\n\n598.\n\nThe extraction of colour is also effected by re-agents. Spirits of wine\nhas a peculiar tendency to attract the juice which tinges plants, and\nbecomes coloured with it often in a very permanent manner. Sulphuric\nacid is very efficient in removing colour, especially from wool and\nsilk, and every one is acquainted with the use of sulphur vapours in\nbleaching.\n\n599.\n\nThe strongest acids have been recommended more recently as more\nexpeditious agents in bleaching.\n\n600.\n\nThe alkaline re-agents produce the same effects by contrary\nmeans--lixiviums alone, oils and fat combined with lixiviums to soap,\nand so forth.\n\n601.\n\nBefore we dismiss this subject, we observe [Pg 240] that it may be\nwell worth while to make certain delicate experiments as to how far\nlight and air exhibit their action in the removal of colour. It might\nbe possible to expose coloured substances to the light under glass\nbells, without air, or filled with common or particular kinds of air.\nThe colours might be those of known fugacity, and it might be observed\nwhether any of the volatilized colour attached itself to the glass or\nwas otherwise perceptible as a deposit or precipitate; whether, again,\nin such a case, this appearance would be perfectly like that which had\ngradually ceased to be visible, or whether it had suffered any change.\nSkilful experimentalists might devise various contrivances with a view\nto such researches.\n\n602.\n\nHaving thus first considered the operations of nature as subservient to\nour proposes, we add a few observations on the modes in which they act\nagainst us.\n\n603.\n\nThe art of painting is so circumstanced that the most beautiful results\nof mind and labour are altered and destroyed in various ways by time.\nHence great pains have been always taken to find durable pigments, and\nso to unite them with each other and with their ground, that their\npermanency might be further insured. The technical history of the\nschools of painting affords sufficient information on this point.\n\n604.\n\nWe may here, too, mention a minor art, to which, in relation to\ndyeing, we are much indebted, namely, the weaving of tapestry. As the\nmanufacturers were enabled to imitate the most delicate shades of\npictures, and hence often brought the most variously coloured materials\ntogether, it was soon observed that the colours were not all equally\ndurable, but that some faded from the tapestry more quickly than\nothers. Hence the most diligent efforts were made to ensure an equal\npermanency to all the colours and their gradations. This object was\nespecially promoted in France, under Colbert, whose regulations to this\neffect constitute an epoch in the history of dyeing. The gay dye which\nonly aimed at a transient beauty, was practised by a particular guild.\nOn the other hand, great pains were taken to define the technical\nprocesses which promised durability.\n\nAnd thus, after considering the artificial extraction, the evanescence,\nand the perishable nature of brilliant appearances of colour, we are\nagain returned to the desideratum of permanency.\n\n\n\n\n## XLIX.\n\n\n\n## NOMENCLATURE.\n\n\n\n605.\n\nAfter what has been adduced respecting the origin, the increase,\nand the affinity of colours, we may be better enabled to judge what\nnomenclature would be desirable in future, and what might be retained\nof that hitherto in use.\n\n606.\n\nThe nomenclature of colours, like all other modes of designation,\nbut especially those employed to distinguish the objects of sense,\nproceeded in the first instance from particular to general, and from\ngeneral back again to particular terms. The name of the species became\na generic name to which the individual was again referred.\n\n607.\n\nThis method might have been followed in consequence of the mutability\nand uncertainty of ancient modes of expression, especially since, in\nthe early ages, more reliance may be supposed to have been placed on\nthe vivid impressions of sense. The qualities of objects were described\nindistinctly, because they were impressed clearly on every imagination.\n\n608.\n\nThe pure chromatic circle was limited, it is true; but, specific as it\nwas, it appears to have been applied to innumerable objects, while it\nwas circumscribed by qualifying characteristics. If we take a glance\nat the copiousness of the Greek and Roman terms, we shall perceive how\nmutable the words were, and how easily each was adapted to almost every\npoint in the colorific circle.--Note W.\n\n609.\n\nIn modern ages terms for many new gradations were introduced in\nconsequence of the various operations of dyeing. Even the colours\nof fashion and their designations, represented an endless series of\nspecific hues. We shall, on occasion, employ the chromatic terminology\nof modern languages, whence it will appear that the aim has gradually\nbeen to introduce more exact definitions, and to individualise and\narrest a fixed and specific state by language equally distinct.\n\n610.\n\nWith regard to the German terminology, it has the advantage of\npossessing four monosyllabic names no longer to be traced to their\norigin, viz., yellow (Gelb), blue, red, green. They represent the most\ngeneral idea of colour to the imagination, without reference to any\nvery specific modification.\n\n611.\n\nIf we were to add two other qualifying terms to each of these four, as\nthus--red-yellow, and yellow-red, red-blue and blue-red, yellow-green\nand green-yellow, blue-green and green-blue,[1] we should express the\ngradations of the chromatic circle with sufficient distinctness; and if\nwe were to add the designations of light and dark, and again define, in\nsome measure, the degree of purity or its opposite by the monosyllables\nblack, white, grey, brown, we should have a tolerably sufficient range\nof expressions to describe the ordinary appearances presented to us,\nwithout troubling ourselves whether they were produced dynamically or\natomically.\n\n612.\n\nThe specific and proper terms in use might, however, still be\nconveniently employed, and we have thus made use of the words orange\nand violet. We have in like manner employed the word \"_purpur_\" to\ndesignate a pure central red, because the secretion of the murex or\n\"_purpura_\" is to be carried to the highest point of culmination by the\naction of the sun-light on fine linen saturated with the juice.\n\n\n[1] This description is suffered to remain because it accounts for the\nterminology employed throughout.--T.\n\n\n\n\nL.\n\n\n## MINERALS.\n\n\n\n613.\n\nThe colours of minerals are all of a chemical nature, and thus the\nmodes in which they are produced may be explained in a general way by\nwhat has been said on the subject of chemical colours.\n\n614.\n\nAmong the external characteristics of minerals, the description of\ntheir colours occupies the first place; and great pains have been\ntaken, in the spirit of modern times, to define and arrest every\nsuch appearance exactly: by this means, however, new difficulties,\nit appears to us, have been created, which occasion no little\ninconvenience in practice.\n\n615.\n\nIt is true, this precision, when we reflect how it arose, carries with\nit its own excuse. The painter has at all times been privileged in\nthe use of colours. The few specific hues, in themselves, admitted of\nno change; but from these, innumerable gradations were artificially\nproduced which imitated the surface of natural objects. It was,\ntherefore, not to be wondered at that these gradations should also be\nadopted as criterions, and that the artist should be invited to produce\ntinted patterns with which the objects of nature might be compared, and\naccording to which they were to receive their designations.\n\n616.\n\nBut, after all, the terminology of colours which has been introduced in\nmineralogy, is open to many objections. The terms, for instance, have\nnot been borrowed from the mineral kingdom, as was possible enough in\nmost cases, but from all kinds of visible objects. Too many specific\nterms have been adopted; and in seeking to establish new definitions\nby combining these, the nomenclators have not reflected that they thus\naltogether efface the image from the imagination, and the idea from\nthe understanding. Lastly, these individual designations of colours,\nemployed to a certain extent as elementary definitions, are not\narranged in the best manner as regards their respective derivation from\neach other: hence, the scholar must learn every single designation,\nand impress an almost lifeless but positive language on his memory.\nThe further consideration of this would be too foreign to our present\nsubject.[1]\n\n\n[1] These remarks have reference to the German mineralogical\nterminology.--T.\n\n\n\n\nLI.\n\n\n## PLANTS.\n\n\n\n617.\n\nThe colours of organic bodies in general may be considered as a higher\nkind of chemical operation, for which reason the ancients employed the\nword concoction, πέψις, to designate the process. All the elementary\ncolours, as well as the combined and secondary hues, appear on the\nsurface of organic productions, while on the other hand, the interior,\nif not colourless, appears, strictly speaking, negative when brought to\nthe light. As we propose to communicate our views respecting organic\nnature, to a certain extent, in another place, we only insert here\nwhat has been before connected with the doctrine of colours, while it\nmay serve as an introduction to the further consideration of the views\nalluded to: and first, of plants.\n\n618.\n\nSeeds, bulbs, roots, and what is generally shut out from the light, or\nimmediately surrounded by the earth, appear, for the most part, white.\n\n619.\n\nPlants reared from seed, in darkness, are white, or approaching to\nyellow. Light, on the other hand, in acting on their colours, acts at\nthe same time on their form.\n\n620.\n\nPlants which grow in darkness make, it is true, long shoots from joint\nto joint: but the stems between two joints are thus longer than they\nshould be; no side stems are produced, and the metamorphosis of the\nplant does not take place.\n\n621.\n\nLight, on the other hand, places it at once in an active state; the\nplant appears green, and the course of the metamorphosis proceeds\nuninterruptedly to the period of reproduction.\n\n622.\n\nWe know that the leaves of the stem are only preparations and\npre-significations of the instruments of florification and\nfructification, and accordingly we can already see colours in the\nleaves of the stem which, as it were, announce the flower from afar, as\nis the case in the amaranthus.\n\n623.\n\nThere are white flowers whose petals have wrought or refined themselves\nto the greatest purity; there are coloured ones, in which the\nelementary hues may be said to fluctuate to and fro. There are some\nwhich, in tending to the higher state, have only partially emancipated\nthemselves from the green of the plant.\n\n624.\n\nFlowers of the same genus, and even of the same kind, are found of all\ncolours. Roses, and particularly mallows, for example, vary through\na great portion of the colorific circle from white to yellow, then\nthrough red-yellow to bright red, and from thence to the darkest hue it\ncan exhibit as it approaches blue.\n\n625.\n\nOthers already begin from a higher degree in the scale, as, for\nexample, the poppy, which is yellow-red in the first instance, and\nwhich afterwards approaches a violet hue.\n\n626.\n\nYet the same colours in species, varieties, and even in families and\nclasses, if not constant, are still predominant, especially the yellow\ncolour: blue is throughout rarer.\n\n627.\n\nA process somewhat similar takes place in the juicy capsule of\nthe fruit, for it increases in colour from the green, through the\nyellowish and yellow, up to the highest red, the colour of the rind\nthus indicating the degree of ripeness. Some are coloured all round,\nsome only on the sunny side, in which last case the augmentation of the\nyellow into red,--the gradations crowding in and upon each other,--may\nbe very well observed.\n\n628.\n\nMany fruits, too, are coloured internally; pure red juices, especially,\nare common.\n\n629.\n\nThe colour which is found superficially in the flower and penetratingly\nin the fruit, spreads itself through all the remaining parts, colouring\nthe roots and the juices of the stem, and this with a very rich and\npowerful hue.\n\n630.\n\nSo, again, the colour of the wood passes from yellow through the\ndifferent degrees of red up to pure red and on to brown. Blue woods are\nunknown to me; and thus in this degree of organisation the active side\nexhibits itself powerfully, although both principles appear balanced in\nthe general green of the plant.\n\n631.\n\nWe have seen above that the germ pushing from the earth is generally\nwhite and yellowish, but that by means of the action of light and air\nit acquires a green colour. The same happens with young leaves of\ntrees, as may be seen, for example, in the birch, the young leaves of\nwhich are yellowish, and if boiled, yield a beautiful yellow juice:\nafterwards they become greener, while the leaves of other trees become\ngradually blue-green.\n\n632.\n\nThus a yellow ingredient appears to belong more essentially to leaves\nthan a blue one; for this last vanishes in the autumn, and the yellow\nof the leaf appears changed to a brown colour. Still more remarkable,\nhowever, are the particular cases where leaves in autumn again become\npure yellow, and others increase to the brightest red.\n\n633.\n\nOther plants, again, may, by artificial treatment be entirely converted\nto a colouring matter, which is as fine, active, and infinitely\ndivisible as any other. Indigo and madder, with which so much is\neffected, are examples: lichens are also used for dyes.\n\n634.\n\nTo this fact another stands immediately opposed; we can, namely,\nextract the colouring part of plants, and, as it were, exhibit it\napart, while the organisation does not on this account appear to suffer\nat all. The colours of flowers may be extracted by spirits of wine, and\ntinge it; the petals meanwhile becoming white.\n\n635.\n\nThere are various modes of acting on flowers and their juices by\nre-agents. This has been done by Boyle in many experiments. Roses are\nbleached by sulphur, and may be restored to their first state by other\nacids; roses are turned green by the smoke of tobacco.\n\n\n\n\nLII.\n\n\n## WORMS, INSECTS, FISHES.\n\n\n\n636.\n\nWith regard to creatures belonging to the lower degrees of\norganisation, we may first observe that worms, which live in the earth\nand remain in darkness and cold moisture, are imperfectly negatively\ncoloured; worms bred in warm moisture and darkness are colourless;\nlight seems expressly necessary to the definite exhibition of colour.\n\n637.\n\nCreatures which live in water, which, although a very dense medium,\nsuffers sufficient light to pass through it, appear more or less\ncoloured. Zoophytes, which appear to animate the purest calcareous\nearth, are mostly white; yet we find corals deepened into the most\nbeautiful yellow-red: in other cells of worms this colour increases\nnearly to bright red.\n\n638.\n\nThe shells of the crustaceous tribe are beautifully designed and\ncoloured, yet it is to be remarked that neither land-snails nor the\nshells of crustacea of fresh water, are adorned with such bright\ncolours as those of the sea.\n\n639.\n\nIn examining shells, particularly such as are spiral, we find that\na series of animal organs, similar to each other, must have moved\nincreasingly forward, and in turning on an axis produced the shell in\na series of chambers, divisions, tubes, and prominences, according to\na plan for ever growing larger. We remark, however, that a tinging\njuice must have accompanied the development of these organs, a juice\nwhich marked the surface of the shell, probably through the immediate\nco-operation of the sea-water, with coloured lines, points, spots, and\nshadings: this must have taken place at regular intervals, and thus\nleft the indications of increasing growth lastingly on the exterior;\nmeanwhile the interior is generally found white or only faintly\ncoloured.\n\n640.\n\nThat such a juice is to be found in shell-fish is, besides,\nsufficiently proved by experience; for the creatures furnish it in its\nliquid and colouring state: the juice of the ink-fish is an example.\nBut a much stronger is exhibited in the red juice found in many\nshell-fish, which was so famous in ancient times, and has been employed\nwith advantage by the moderns. There is, it appears, in the entrails of\nmany of the crustaceous tribe a certain vessel which is filled with a\nred juice; this contains a very strong and durable colouring substance,\nso much so that the entire creature may be crushed and boiled, and\nyet out of this broth a sufficiently strong tinging liquid may be\nextracted. But the little vessel filled with colour may be separated\nfrom the animal, by which means of course a concentrated juice is\ngained.\n\n641.\n\nThis juice has the property that when exposed to light and air it\nappears first yellowish, then greenish; it then passes to blue, then to\na violet, gradually growing redder; and lastly, by the action of the\nsun, and especially if transferred to cambric, it assumes a pure bright\nred colour.\n\n642.\n\nThus we should here have an augmentation, even to culmination, on the\n_minus_ side, which we cannot easily meet with in inorganic cases;\nindeed, we might almost call this example a passage through the\nwhole scale, and we are persuaded that by due experiments the entire\nrevolution of the circle might really be effected, for there is no\ndoubt that by acids duly employed, the pure red may be pushed beyond\nthe culminating point towards scarlet.\n\n643.\n\nThis juice appears on the one hand to be connected with the phenomena\nof reproduction, eggs being found, the embryos of future shell-fish,\nwhich contain a similar colouring principle. On the other hand, in\nanimals ranking higher in the scale of being, the secretion appears to\nbear some relation to the development of the blood. The blood exhibits\nsimilar properties in regard to colour; in its thinnest state it\nappears yellow; thickened, as it is found in the veins, it appears red;\nwhile the arterial blood exhibits a brighter red, probably owing to the\noxydation which takes place by means of breathing. The venous blood\napproaches more to violet, and by this mutability denotes the tendency\nto that augmentation and progression which are now familiar to us.\n\n644.\n\nBefore we quit the element whence we derived the foregoing examples,\nwe may add a few observations on fishes, whose scaly surface is\ncoloured either altogether in stripes, or in spots, and still oftener\nexhibits a certain iridescent appearance, indicating the affinity of\nthe scales with the coats of shell-fish, mother-of-pearl, and even\nthe pearl itself. At the same time it should not be forgotten that\nwarmer climates, the influence of which extends to the watery regions,\nproduce, embellish, and enhance these colours in fishes in a still\ngreater degree.\n\n645.\n\nIn Otaheite, Forster observed fishes with beautifully iridescent\nsurfaces, and this effect was especially apparent at the moment when\nthe fish died. We may here call to mind the hues of the chameleon,\nand other similar appearances; for when similar facts are presented\ntogether, we are better enabled to trace them.\n\n646.\n\nLastly, although not strictly in the same class, the iridescent\nappearance of certain molluscæ may be mentioned, as well as the\nphosphorescence which, in some marine creatures, it is said becomes\niridescent just before it vanishes.\n\n647.\n\nWe now turn our attention to those creatures which belong to light,\nair and dry warmth, and it is here that we first find ourselves in\nthe living region of colours. Here, in exquisitely organised parts,\nthe elementary colours present themselves in their greatest purity\nand beauty. They indicate, however, that the creatures they adorn,\nare still low in the scale of organisation, precisely because these\ncolours can thus appear, as it were, unwrought. Here, too, heat seems\nto contribute much to their development.\n\n648.\n\nWe find insects which may be considered altogether as concentrated\ncolouring matter; among these, the cochineals especially are\ncelebrated; with regard to these we observe that their mode of settling\non vegetables, and even nestling in them, at the same time produces\nthose excrescences which are so useful as mordants in fixing colours.\n\n649.\n\nBut the power of colour, accompanied by regular organisation, exhibits\nitself in the most striking manner in those insects which require a\nperfect metamorphosis for their development--in scarabæ, and especially\nin butterflies.\n\n650.\n\nThese last, which might be called true productions of light and air,\noften exhibit the most beautiful colours, even in their chrysalis\nstate, indicating the future colours of the butterfly; a consideration\nwhich, if pursued further hereafter, must undoubtedly afford a\nsatisfactory insight into many a secret of organised being.\n\n651.\n\nIf, again, we examine the wings of the butterfly more accurately, and\nin its net-like web discover the rudiments of an arm, and observe\nfurther the mode in which this, as it were, flattened arm is covered\nwith tender plumage and constituted an organ of flying; we believe\nwe recognise a law according to which the great variety of tints is\nregulated. This will be a subject for further investigation hereafter.\n\n652.\n\nThat, again, heat generally has an influence on the size of the\ncreature, on the accomplishment of the form, and on the greater beauty\nof the colours, hardly needs to be remarked.\n\n\n\n\n## LIII.\n\n\n\n## BIRDS.\n\n\n\n653.\n\nThe more we approach the higher organisations, the more it becomes\nnecessary to limit ourselves to a few passing observations; for all the\nnatural conditions of such organised beings are the result of so many\npremises, that, without having at least hinted at these, our remarks\nwould only appear daring, and at the same time insufficient.\n\n654.\n\nWe find in plants, that the consummate flower and fruit are, as it\nwere, rooted in the stem, and that they are nourished by more perfect\njuices than the original roots first afforded; we remark, too,\nthat parasitical plants which derive their support from organised\nstructures, exhibit themselves especially endowed as to their energies\nand qualities. We might in some sense compare the feathers of birds\nwith plants of this description; the feathers spring up as a last\nstructural result from the surface of a body which has yet much in\nreserve for the completion of the external economy, and thus are very\nrichly endowed organs.\n\n655.\n\nThe quills not only grow proportionally to a considerable size, but are\nthroughout branched, by which means they properly become feathers, and\nmany of these feathered branches are again subdivided; thus, again,\nrecalling the structure of plants.\n\n656.\n\nThe feathers are very different in shape and size, but each still\nremains the same organ, forming and transforming itself according to\nthe constitution of the part of the body from which it springs.\n\n657.\n\nWith the form, the colour also becomes changed, and a certain law\nregulates the general order of hues as well as that particular\ndistribution by which a single feather becomes party coloured, It\nis from this that all combination of variegated plumage arises, and\nwhence, at last, the eyes in the peacock's tail are produced. It is\na result similar to that which we have already unfolded in treating\nof the metamorphosis of plants, and which we shall take an early\nopportunity to prove.\n\n658.\n\nAlthough time and circumstances compel us here to pass by this organic\nlaw, yet we are bound to refer to the chemical operations which\ncommonly exhibit themselves in the tinting of feathers in a mode now\nsufficiently known to us.\n\n659.\n\nPlumage is of all colours, yet, on the whole, yellow deepening to red\nis commoner than blue.\n\n660.\n\nThe operation of light on the feathers and their colours, is to be\nremarked in all cases. Thus, for example, the feathers on the breast of\ncertain parrots, are strictly yellow; the scale-like anterior portion,\nwhich is acted on by the light, is deepened from yellow to red. The\nbreast of such a bird appears bright-red, but if we blow into the\nfeathers the yellow appears.\n\n661.\n\nThe exposed portion of the feathers is in all cases very different\nfrom that which, in a quiet state, is covered; it is only the exposed\nportion, for instance, in ravens, which exhibits the iridescent\nappearance; the covered portion does not: from which indication, the\nfeathers of the tail when ruffled together, may be at once placed in\nthe natural order again.\n\n\n\n\nLIV.\n\n\n## MAMMALIA AND HUMAN BEINGS.\n\n\n\n662.\n\nHere the elementary colours begin to leave us altogether. We are\narrived at the highest degree of the scale, and shall not dwell on its\ncharacteristics long.\n\n663.\n\nAn animal of this class is distinguished among the examples of\norganised being. Every thing that exhibits itself about him is living.\nOf the internal structure we do not speak, but confine ourselves\nbriefly to the surface. The hairs are already distinguished from\nfeathers, inasmuch as they belong more to the skin, inasmuch as they\nare simple, thread-like, not branched. They are however, like feathers,\nshorter, longer, softer, and firmer, colourless or coloured, and all\nthis in conformity to laws which might be defined.\n\n664.\n\nWhite and black, yellow, yellow-red and brown, alternate in various\nmodifications, but they never appear in such a state as to remind us\nof the elementary hues. On the contrary, they are all broken colours\nsubdued by organic concoction, and thus denote, more or less, the\nperfection of life in the being they belong to.\n\n665.\n\nOne of the most important considerations connected with morphology,\nso far as it relates to surfaces, is this, that even in quadrupeds\nthe spots of the skin have a relation with the parts underneath\nthem. Capriciously as nature here appears, on a hasty examination,\nto operate, she nevertheless consistently observes a secret law. The\ndevelopment and application of this, it is true, are reserved only for\naccurate and careful investigation and sincere co-operation.\n\n666.\n\nIf in some animals portions appear variegated with positive colours,\nthis of itself shows how far such creatures are removed from a perfect\norganisation; for, it may be said, the nobler a creature is, the more\nall the mere material of which he is composed, is disguised by being\nwrought together; the more essentially his surface corresponds with the\ninternal organisation, the less can it exhibit the elementary colours.\nWhere all tends to make up a perfect whole, any detached specific\ndevelopments cannot take place.\n\n667.\n\nOf man we have little to say, for he is entirely distinct from the\ngeneral physiological results of which we now treat. So much in this\ncase is in affinity with the internal structure, that the surface can\nonly be sparingly endowed.\n\n668.\n\nWhen we consider that brutes are rather encumbered than advantageously\nprovided with intercutaneous muscles; when we see that much that is\nsuperfluous tends to the surface, as, for instance, large ears and\ntails, as well as hair, manes, tufts; we see that nature, in such\ncases, had much to give away and to lavish.\n\n669.\n\nOn the contrary, the general surface of the human form is smooth and\nclean, and thus in the most perfect examples, the beautiful forms are\napparent; for it may be remarked in passing, that a superfluity of\nhair on the chest, arms, and lower limbs, rather indicates weakness\nthan strength. Poets only have sometimes been induced, probably by the\nexample of the ferine nature, so strong in other respects, to extol\nsimilar attributes in their rough heroes.\n\n670.\n\nBut we have here chiefly to speak of colour, and observe that the\ncolour of the human skin, in all its varieties, is never an elementary\ncolour, but presents, by means of organic concoction, a highly\ncomplicated result.--Note X.\n\n671.\n\nThat the colour of the skin and hair has relation with the differences\nof character, is beyond question; and we are led to conjecture that the\ncircumstance of one or other organic system predominating, produces\nthe varieties we see. A similar hypothesis may be applied to nations,\nin which case it might perhaps be observed, that certain colours\ncorrespond with certain confirmations, which has always been observed\nof the negro physiognomy.\n\n672.\n\nLastly, we might here consider the problematical question, whether all\nhuman forms and hues are not equally beautiful, and whether custom\nand self-conceit are not the causes why one is preferred to another?\nWe venture, however, after what has been adduced, to assert that the\nwhite man, that is, he whose surface varies from white to reddish,\nyellowish, brownish, in short, whose surface appears most neutral in\nhue and least inclines to any particular or positive colour, is the\nmost beautiful. On the same principle a similar point of perfection in\nhuman conformation may be defined hereafter, when the question relates\nto form. We do not imagine that this long-disputed question is to be\nthus, once for all, settled, for there are persons enough who have\nreason to leave this significancy of the exterior in doubt; but we thus\nexpress a conclusion, derived from observation and reflection, such\nas might suggest itself to a mind aiming at a satisfactory decision.\nWe subjoin a few observations connected with the elementary chemical\ndoctrine of colours.--Note Y.\n\n\n\n\nLV.\n\n\n## PHYSICAL AND CHEMICAL EFFECTS OF THE TRANSMISSION OF LIGHT THROUGH\n\nCOLOURED MEDIUMS.\n\n\n673.\n\nThe physical and chemical effects of colourless light are known, so\nthat it is unnecessary here to describe them at length. Colourless\nlight exhibits itself under various conditions as exciting warmth, as\nimparting a luminous quality to certain bodies, as promoting oxydation\nand de-oxydation. In the modes and degrees of these effects many\nvarieties take place, but no difference is found indicating a principle\nof contrast such as we find in the transmission of coloured light. We\nproceed briefly to advert to this.\n\n674.\n\nLet the temperature of a dark room be observed by means of a very\nsensible air-thermometer; if the bulb is then brought to the direct sun\nlight as it shines into the room, nothing is more natural than that the\nfluid should indicate a much higher degree of warmth. If upon this we\ninterpose coloured glasses, it follows again quite naturally that the\ndegree of warmth must be lowered; first, because the operation of the\ndirect light is already somewhat impeded by the glass, and again, more\nespecially, because a coloured glass, as a dark medium, admits less\nlight through it.\n\n675.\n\nBut here a difference in the excitation of warmth exhibits itself to\nthe attentive observer, according to the colour of the glass. The\nyellow and the yellow-red glasses produce a higher temperature than the\nblue and blue-red, the difference being considerable.\n\n676.\n\nThis experiment may be made with the prismatic spectrum. The\ntemperature of the room being first remarked on the thermometer, the\nblue coloured light is made to fall on the bulb, when a somewhat higher\ndegree of warmth is exhibited, which still increases as the other\ncolours are gradually brought to act on the mercury. If the experiment\nis made with the water-prism, so that the white light can be retained\nin the centre, this, refracted indeed, but not yet coloured light, is\nthe warmest; the other colours, stand in relation to each other as\nbefore.\n\n677.\n\nAs we here merely describe, without undertaking to deduce or explain\nthis phenomenon, we only remark in passing, that the pure light is by\nno means abruptly and entirely at an end with the red division in the\nspectrum, but that a refracted light is still to be observed deviating\nfrom its course and, as it were, insinuating itself beyond the\nprismatic image, so that on closer examination it will hardly be found\nnecessary to take refuge in invisible rays and their refraction.\n\n678.\n\nThe communication of light by means of coloured mediums exhibits the\nsame difference. The light communicates itself to Bologna phosphorus\nthrough blue and violet glasses, but by no means through yellow and\nyellow-red glasses. It has been even remarked that the phosphori which\nhave been rendered luminous under violet and blue glasses, become\nsooner extinguished when afterwards placed under yellow and yellow-red\nglasses than those which have been suffered to remain in a dark room\nwithout any further influence.\n\n679.\n\nThese experiments, like the foregoing, may also be made by means of the\nprismatic spectrum, when the same results take place.\n\n680.\n\nTo ascertain the effect of coloured light on oxydation and\nde-oxydation, the following means may be employed:--Let moist,\nperfectly white muriate of silver[1] be spread on a strip of paper;\nplace it in the light, so that it may become to a certain degree grey,\nand then cut it in three portions. Of these, one may be preserved\nin a book, as a specimen of this state; let another be placed under\na yellow-red, and the third under a blue-red glass. The last will\nbecome a darker grey, and exhibit a de-oxydation; the other, under the\nyellow-red glass, will, on the contrary, become a lighter grey, and\nthus approach nearer to the original state of more perfect oxydation.\nThe change in both may be ascertained by a comparison with the\nunaltered specimen.\n\n681.\n\nAn excellent apparatus has been contrived to perform these experiments\nwith the prismatic image. The results are analogous to those already\nmentioned, and we shall hereafter give the particulars, making use\nof the labours of an accurate observer, who has been for some time\ncarefully prosecuting these experiments.[2]\n\n\n[1] Now generally called chloride of silver: the term in the original\nis Hornsilber.--T.\n\n[2] The individual alluded to was Seebeck: the result of his\nexperiments was published in the second volume.--T.\n\n\n\n\nLVI.\n\n\n## CHEMICAL EFFECT IN DIOPTRICAL ACHROMATISM.\n\n\n\n682.\n\nWe first invite our readers to turn to what has been before observed on\nthis subject (285, 298), to avoid unnecessary repetition here.\n\n683.\n\nWe can thus give a glass the property of producing much wider coloured\nedges without refracting more strongly than before, that is, without\ndisplacing the object much more perceptibly.\n\n684.\n\nThis property is communicated to the glass by means of metallic oxydes.\nMinium, melted and thoroughly united with a pure glass, produces this\neffect, and thus flint-glass (291) is prepared with oxyde of lead.\nExperiments of this kind have been carried farther, and the so-called\nbutter of antimony, which, according to a new preparation, may be\nexhibited as a pure fluid, has been made use of in hollow lenses and\nprisms, producing a very strong appearance of colour with a very\nmoderate refraction, and presenting the effect which we have called\nhyperchromatism in a very vivid manner.\n\n685.\n\nIn common glass, the alkaline nature obviously preponderates, since\nit is chiefly composed of sand and alkaline salts; hence a series of\nexperiments, exhibiting the relation of perfectly alkaline fluids to\nperfect acids, might lead to useful results.\n\n686.\n\nFor, could the maximum and minimum be found, it would be a question\nwhether a refracting medium could not be discovered, in which the\nincreasing and diminishing appearance of colour, (an effect almost\nindependent of refraction,) could not be done away with altogether,\nwhile the displacement of the object would be unaltered.\n\n687.\n\nHow desirable, therefore, it would be with regard to this last point,\nas well as for the elucidation of the whole of this third division of\nour work, and, indeed, for the elucidation of the doctrine of colours\ngenerally, that those who are occupied in chemical researches, with new\nviews ever opening to them, should take this subject in hand, pursuing\ninto more delicate combinations what we have only roughly hinted at,\nand prosecuting their inquiries with reference to science as a whole.\n\n\n\n\n## PART IV.\n\n\n\n## GENERAL CHARACTERISTICS.\n\n\n\n688.\n\nWe have hitherto, in a manner forcibly, kept phenomena asunder,\nwhich, partly from their nature, partly in accordance with our mental\nhabits, have, as it were, constantly sought to be reunited. We have\nexhibited them in three divisions. We have considered colours, first,\nas transient, the result of an action and re-action in the eye\nitself; next, as passing effects of colourless, light-transmitting,\ntransparent, or opaque mediums on light; especially on the luminous\nimage; lastly, we arrived at the point where we could securely\npronounce them as permanent, and actually inherent in bodies.\n\n689.\n\nIn following this order we have as far as possible endeavoured to\ndefine, to separate, and to class the appearances. But now that we\nneed no longer be apprehensive of mixing or confounding them, we may\nproceed, first, to state the general nature of these appearances\nconsidered abstractedly, as an independent circle of facts, and, in the\nnext place, to show how this particular circle is connected with other\nclasses of analogous phenomena in nature.\n\n\n## THE FACILITY WITH WHICH COLOUR APPEARS.\n\n\n\n690.\n\nWe have observed that colour under many conditions appears very easily.\nThe susceptibility of the eye with regard to light, the constant\nre-action of the retina against it, produce instantaneously a slight\niridescence. Every subdued light may be considered as coloured, nay, we\nought to call any light coloured, inasmuch as it is seen. Colourless\nlight, colourless surfaces, are, in some sort, abstract ideas; in\nactual experience we can hardly be said to be aware of them.--Note Z.\n\n691.\n\nIf light impinges on a colourless body, is reflected from it or passes\nthrough it, colour immediately appears; but it is necessary here to\nremember what has been so often urged by us, namely, that the leading\nconditions of refraction, reflection, &c., are not of themselves\nsufficient to produce the appearance. Sometimes, it is true, light acts\nwith these merely as light, but oftener as a defined, circumscribed\nappearance, as a luminous image. The semi-opacity of the medium is\noften a necessary condition; while half, and double shadows, are\nrequired for many coloured appearances. In all cases, however, colour\nappears instantaneously. We find, again, that by means of pressure,\nbreathing heat (432, 471), by various kinds of motion and alteration\non smooth clean surfaces (461), as well as on colourless fluids (470),\ncolour is immediately produced.\n\n692.\n\nThe slightest change has only to take place in the component parts\nof bodies, whether by immixture with other particles or other such\neffects, and colour either makes its appearance or becomes changed.\n\n\n## THE FORCE OF COLOUR.\n\n\n\n693.\n\nThe physical colours, and especially those of the prism, were formerly\ncalled \"_colores emphatici_,\" on account of their extraordinary beauty\nand force. Strictly speaking, however, a high degree of effect may be\nascribed to all appearances of colour, assuming that they are exhibited\nunder the purest and most perfect conditions.\n\n694.\n\nThe dark nature of colour, its full rich quality, is what produces\nthe grave, and at the same time fascinating impression we sometimes\nexperience, and as colour is to be considered a condition of light,\nso it cannot dispense with light as the co-operating cause of its\nappearance, as its basis or ground; as a power thus displaying and\nmanifesting colour.\n\n\n## THE DEFINITE NATURE OF COLOUR.\n\n\n\n695.\n\nThe existence and the relatively definite character of colour are one\nand the same thing. Light displays itself and the face of nature, as\nit were, with a general indifference, informing us as to surrounding\nobjects perhaps devoid of interest or importance; but colour is at all\ntimes specific, characteristic, significant.\n\n696.\n\nConsidered in a general point of view, colour is determined towards one\nof two sides. It thus presents a contrast which we call a polarity, and\nwhich we may fitly designate by the expressions _plus_ and _minus_.\n\n    _Plus.                       Minus_.\n\n    Yellow.                        Blue.\n    Action.                        Negation.[1]\n    Light.                         Shadow.\n    Brightness.                    Darkness.\n    Force.                         Weakness.\n    Warmth.                        Coldness.\n    Proximity.                     Distance.\n    Repulsion                      Attraction.\n    Affinity with acids.           Affinity with alkalis.\n\n\n## COMBINATION OF THE TWO PRINCIPLES.\n\n\n\n697.\n\nIf these specific, contrasted principles are combined, the respective\nqualities do not therefore destroy each other: for if in this\nintermixture the ingredients are so perfectly balanced that neither\nis to be distinctly recognised, the union again acquires a specific\ncharacter; it appears as a quality by itself in which we no longer\nthink of combination. This union we call green.\n\n698.\n\nThus, if two opposite phenomena springing from the same source do not\ndestroy each other when combined, but in their union present a third\nappreciable and pleasing appearance, this result at once indicates\ntheir harmonious relation. The more perfect result yet remains to be\nadverted to.\n\n\n## AUGMENTATION TO RED.\n\n\n\n699.\n\nBlue and yellow do not admit of increased intensity without presently\nexhibiting a new appearance in addition to their own. Each colour, in\nits lightest state, is a dark; if condensed it must become darker, but\nthis effect no sooner takes place than the hue assumes an appearance\nwhich we designate by the word reddish.\n\n700.\n\nThis appearance still increases, so that when the highest degree of\nintensity is attained it predominates over the original hue. A powerful\nimpression of light leaves the sensation of red on the retina. In the\nprismatic yellow-red which springs directly from the yellow, we hardly\nrecognise the yellow.\n\n701.\n\nThis deepening takes place again by means of colourless\nsemi-transparent mediums, and here we see the effect in its utmost\npurity and extent. Transparent fluids, coloured with any given hues, in\na series of glass-vessels, exhibit it very strikingly. The augmentation\nis unremittingly rapid and constant; it is universal, and obtains in\nphysiological as well as in physical and chemical colours.\n\n\n## JUNCTION OF THE TWO AUGMENTED EXTREMES.\n\n\n\n702.\n\nAs the extremes of the simple contrast produce a beautiful and\nagreeable appearance by their union, so the deepened extremes on being\nunited, will present a still more fascinating colour; indeed, it might\nnaturally be expected that we should here find the acme of the whole\nphenomenon.\n\nCOMPLETENESS THE RESULT OF VARIETY.\n\n\n703.\n\nAnd such is the fact, for pure red appears; a colour to which, from its\nexcellence, we have appropriated the term \"purpur.\"[2]\n\n704.\n\nThere are various modes in which pure red may appear. By bringing\ntogether the violet edge and yellow-red border in prismatic\nexperiments, by continued augmentation in chemical operations, and by\nthe organic contrast in physiological effects.\n\n705.\n\nAs a pigment it cannot be produced by intermixture or union, but\nonly by arresting the hue in substances chemically acted on, at the\nhigh culminating point. Hence the painter is justified in assuming\nthat there are _three_ primitive colours from which he combines all\nthe others. The natural philosopher, on the other hand, assumes only\n_two_ elementary colours, from which he, in like manner, developes and\ncombines the rest.\n\n\n## COMPLETENESS THE RESULT OF VARIETY IN COLOUR.\n\n\n\n706.\n\nThe various appearances of colour arrested in their different degrees,\nand seen in juxtaposition, produce a whole. This totality is harmony to\nthe eye.\n\n707.\n\nThe chromatic circle has been gradually presented to us; the\nvarious relations of its progression are apparent to us. Two pure\noriginal principles in contrast, are the foundation of the whole;\nan augmentation manifests itself by means of which both approach a\nthird state; hence there exists on both sides a lowest and highest,\na simplest and most qualified state. Again, two combinations present\nthemselves; first that of the simple primitive contrasts, then that of\nthe deepened contrasts.\n\n\n## HARMONY OF THE COMPLETE STATE.\n\n\n\n708.\n\nThe whole ingredients of the chromatic scale, seen in juxtaposition,\nproduce an harmonious impression on the eye. The difference between the\nphysical contrast and harmonious opposition in all its extent should\nnot be overlooked. The first resides in the pure restricted original\ndualism, considered in its antagonizing elements; the other results\nfrom the fully developed effects of the complete state.\n\n709.\n\nEvery single opposition in order to be harmonious must comprehend the\nwhole. The physiological experiments are sufficiently convincing\non this point. A development of all the possible contrasts of the\nchromatic scale will be shortly given.[3]\n\n\n## FACILITY WITH WHICH COLOUR MAY BE MADE TO TEND EITHER TO THE PLUS OR\n\nMINUS SIDE.\n\n\n710.\n\nWe have already had occasion to take notice of the mutability of colour\nin considering its so-called augmentation and progressive variations\nround the whole circle; but the hues even pass and repass from one side\nto the other, rapidly and of necessity.\n\n711.\n\nPhysiological colours are different in appearance as they happen\nto fall on a dark or on a light ground. In physical colours the\ncombination of the objective and subjective experiments is very\nremarkable. The epoptical colours, it appears, are contrasted according\nas the light shines through or upon them. To what extent the chemical\ncolours may be changed by fire and alkalis, has been sufficiently shown\nin its proper place.\n\n\n## EVANESCENCE OF COLOUR.\n\n\n\n712.\n\nAll that has been adverted to as subsequent to the rapid excitation\nand definition of colour, immixture, augmentation, combination,\nseparation, not forgetting the law of compensatory harmony, all takes\nplace with the greatest rapidity and facility; but with equal quickness\ncolour again altogether disappears.\n\n713.\n\nThe physiological appearances are in no wise to be arrested; the\nphysical last only as long as the external condition lasts; even the\nchemical colours have great mutability, they may be made to pass and\nrepass from one side to the other by means of opposite re-agents, and\nmay even be annihilated altogether.\n\n\n## PERMANENCE OF COLOUR.\n\n\n\n714.\n\nThe chemical colours afford evidence of very great duration. Colours\nfixed in glass by fusion, and by nature in gems, defy all time and\nre-action.\n\n715.\n\nThe art of dyeing again fixes colour very powerfully. The hues of\npigments which might otherwise be easily rendered mutable by re-agents,\nmay be communicated to substances in the greatest permanency by means\nof mordants.\n\n\n[1] Wirkung, Beraubung; the last would be more literally rendered\n_privation_. The author has already frequently made use of the terms\n_active_ and _passive_ as equivalent to _plus_ and _minus_.--T.\n\n[2] Wherever this word occurs incidentally it is translated _pure red_,\nthe English word _purple_ being generally employed to denote a colour\nsimilar to violet.--T.\n\n[3] No diagram or table of this kind was ever given by the author.--T.\n\n\n\n\n## PART V.\n\n\n\n## RELATION TO OTHER PURSUITS--RELATION TO PHILOSOPHY.\n\n\n\n716.\n\nThe investigator of nature cannot be required to be a philosopher,\nbut it is expected that he should so far have attained the habit of\nphilosophizing, as to distinguish himself essentially from the world,\nin order to associate himself with it again in a higher sense. He\nshould form to himself a method in accordance with observation, but\nhe should take heed not to reduce observation to mere notion, to\nsubstitute words for this notion, and to use and deal with these words\nas if they were things. He should be acquainted with the labours of\nphilosophers, in order to follow up the phenomena which have been the\nsubject of his observation, into the philosophic region.\n\n717.\n\nIt cannot be required that the philosopher should be a naturalist, and\nyet his co-operation in physical researches is as necessary as it is\ndesirable. He needs not an acquaintance with details for this, but only\na clear view of those conclusions where insulated facts meet.\n\n718.\n\nWe have before (175) alluded to this important consideration, and\nrepeat it here where it is in its place. The worst that can happen\nto physical science as well as to many other kinds of knowledge is,\nthat men should treat a secondary phenomenon as a primordial one, and\n(since it is impossible to derive the original fact from the secondary\nstate), seek to explain what is in reality the cause by an effect made\nto usurp its place. Hence arises an endless confusion, a mere verbiage,\na constant endeavour to seek and to find subterfuges whenever truth\npresents itself and threatens to be overpowering.\n\n719.\n\nWhile the observer, the investigator of nature, is thus dissatisfied\nin finding that the appearances he sees still contradict a received\ntheory, the philosopher can calmly continue to operate in his abstract\ndepartment on a false result, for no result is so false but that it can\nbe made to appear valid, as form without substance, by some means or\nother.\n\n720.\n\nIf, on the other hand, the investigator of nature can attain to the\nknowledge of that which we have called a primordial phenomenon, he is\nsafe; and the philosopher with him. The investigator of nature is\nsafe, since he is persuaded that he has here arrived at the limits\nof his science, that he finds himself at the height of experimental\nresearch; a height whence he can look back upon the details of\nobservation in all its steps, and forwards into, if he cannot enter,\nthe regions of theory. The philosopher is safe, for he receives\nfrom the experimentalist an ultimate fact, which, in his hands, now\nbecomes an elementary one. He now justly pays little attention to\nappearances which are understood to be secondary, whether he already\nfinds them scientifically arranged, or whether they present themselves\nto his casual observation scattered and confused. Should he even be\ninclined to go over this experimental ground himself, and not be\naverse to examination in detail, he does this conveniently, instead of\nlingering too long in the consideration of secondary and intermediate\ncircumstances, or hastily passing them over without becoming accurately\nacquainted with them.\n\n721.\n\nTo place the doctrine of colours nearer, in this sense, within the\nphilosopher's reach, was the author's wish; and although the execution\nof his purpose, from various causes, does not correspond with his\nintention, he will still keep this object in view in an intended\nrecapitulation, as well as in the polemical and historical portions of\nhis work; for he will have to return to the consideration of this point\nhereafter, on an occasion where it will be necessary to speak with less\nreserve.\n\n\n## RELATION TO MATHEMATICS.\n\n\n\n722.\n\nIt may be expected that the investigator of nature, who proposes to\ntreat the science of natural philosophy in its entire range, should be\na mathematician. In the middle ages, mathematics was the chief organ by\nmeans of which men hoped to master the secrets of nature, and even now,\ngeometry in certain departments of physics, is justly considered of\nfirst importance.\n\n723.\n\nThe author can boast of no attainments of this kind, and on this\naccount confines himself to departments of science which are\nindependent of geometry; departments which in modern times have been\nopened up far and wide.\n\n724.\n\nIt will be universally allowed that mathematics, one of the noblest\nauxiliaries which can be employed by man, has, in one point of view,\nbeen of the greatest use to the physical sciences; but that, by a\nfalse application of its methods, it has, in many respects, been\nprejudicial to them, is also not to be denied; we find it here and\nthere reluctantly admitted.\n\n725.\n\nThe theory of colours, in particular, has suffered much, and its\nprogress has been incalculably retarded by having been mixed up with\noptics generally, a science which cannot dispense with mathematics;\nwhereas the theory of colours, in strictness, may be investigated quite\nindependently of optics.\n\n726.\n\nBut besides this there was an additional evil. A great mathematician\nwas possessed with an entirely false notion on the physical origin of\ncolours; yet, owing to his great authority as a geometer, the mistakes\nwhich he committed as an experimentalist long became sanctioned in the\neyes of a world ever fettered in prejudices.\n\n727.\n\nThe author of the present inquiry has endeavoured throughout to keep\nthe theory of colours distinct from the mathematics, although there\nare evidently certain points where the assistance of geometry would be\ndesirable. Had not the unprejudiced mathematicians, with whom he has\nhad, or still has, the good fortune to be acquainted, been prevented\nby other occupations from making common cause with him, his work would\nnot have wanted some merit in this respect. But this very want may be\nin the end advantageous, since it may now become the object of the\nenlightened mathematician to ascertain where the doctrine of colours is\nin need of his aid, and how he can contribute the means at his command\nwith a view to the complete elucidation of this branch of physics.\n\n728.\n\nIn general it were to be wished that the Germans, who render such\ngood service to science, while they adopt all that is good from other\nnations, could by degrees accustom themselves to work in concert. We\nlive, it must be confessed, in an age, the habits of which are directly\nopposed to such a wish. Every one seeks, not only to be original in\nhis views, but to be independent of the labours of others, or at least\nto persuade himself that he is so, even in the course of his life\nand occupation. It is very often remarked that men who undoubtedly\nhave accomplished much, quote themselves only, their own writings,\njournals, and compendiums; whereas it would be far more advantageous\nfor the individual, and for the world, if many were devoted to a common\npursuit. The conduct of our neighbours the French is, in this respect,\nworthy of imitation; we have a pleasing instance in Cuvier's preface\nto his \"Tableau Élémentaire de l'Histoire Naturelle des Animaux.\"\n\n729.\n\nHe who has observed science and its progress with an unprejudiced eye,\nmight even ask whether it is desirable that so many occupations and\naims, though allied to each other, should be united in one person, and\nwhether it would not be more suitable for the limited powers of the\nhuman mind to distinguish, for example, the investigator and inventor,\nfrom him who employs and applies the result of experiment? Astronomers,\nwho devote themselves to the observation of the heavens and the\ndiscovery or enumeration of stars, have in modern times formed, to a\ncertain extent, a distinct class from those who calculate the orbits,\nconsider the universe in its connexion, and more accurately define its\nlaws. The history of the doctrine of colours will often lead us back to\nthese considerations.\n\n\n## RELATION TO THE TECHNICAL OPERATIONS OF THE DYER.\n\n\n\n730.\n\nIf in our labours we have gone out of the province of the\nmathematician, we have, on the other hand, endeavoured to meet the\npractical views of the dyer; and although the chapter which treats\nof colour in a chemical point of view is not the most complete and\ncircumstantial, yet in that portion, as well as in our general\nobservations respecting colour, the dyer will find his views assisted\nfar more than by the theory hitherto in vogue, which failed to afford\nhim any assistance.\n\n731.\n\nIt is curious, in this view, to take a glance at the works containing\ndirections on the art of dyeing. As the Catholic, on entering his\ntemple, sprinkles himself with holy water, and after bending the knee,\nproceeds perhaps to converse with his friends on his affairs, without\nany especial devotion; so all the treatises on dyeing begin with a\nrespectful allusion to the accredited theory, without afterwards\nexhibiting a single trace of any principle deduced from this theory,\nor showing that it has thrown light on any part of the art, or that it\noffers any useful hints in furtherance of practical methods.\n\n732.\n\nOn the other hand, there are men who, after having become thoroughly\nand experimentally acquainted with the nature of dyes, have not been\nable to reconcile their observations with the received theory; who\nhave, in short, discovered its weak points, and sought for a general\nview more consonant to nature and experience. When we come to the names\nof Castel and Gülich, in our historical review, we shall have occasion\nto enter into this more fully, and an opportunity will then present\nitself to show that an assiduous experience in taking advantage of\nevery accident may, in fact, be said almost to exhaust the knowledge\nof the province to which it is confined. The high and complete result\nis then submitted to the theorist, who, if he examines facts with\naccuracy, and reasons with candour, will find such materials eminently\nuseful as a basis for his conclusions.--Note A A.\n\n\n## RELATION TO PHYSIOLOGY AND PATHOLOGY.\n\n\n\n733.\n\nIf the phenomena adduced in the chapter where colours were considered\nin a physiological and pathological view are for the most part\ngenerally known, still some new views, mixed up with them, will not be\nunacceptable to the physiologist. We especially hope to have given him\ncause to be satisfied by classing certain phenomena which stood alone,\nunder analogous facts, and thus, in some measure, to have prepared the\nway for his further investigations.\n\n734.\n\nThe appendix on pathological colours, again, is admitted to be scanty\nand unconnected. We reflect, however, that Germany can boast of men who\nare not only highly experienced in this department, but are likewise so\ndistinguished for general cultivation, that it can cost them but little\nto revise this portion, to complete what has been sketched, and at the\nsame time to connect it with the higher facts of organisation.\n\n\n## RELATION TO NATURAL HISTORY.\n\n\n\n735.\n\nIf we may at all hope that natural history will gradually be modified\nby the principle of deducing the ordinary appearances of nature from\nhigher phenomena, the author believes he may have given some hints\nand introductory views bearing on this object also. As colour, in its\ninfinite variety, exhibits itself on the surface of living beings, it\nbecomes an important part of the outward indications, by means of which\nwe can discover what passes underneath.\n\n736.\n\nIn one point of view it is certainly not to be too much relied on, on\naccount of its indefinite and mutable nature; yet even this mutability,\ninasmuch as it exhibits itself as a constant quality, again becomes\na criterion of a mutable vitality; and the author wishes nothing\nmore than that time may be granted him to develop the results of his\nobservations on this subject more fully; here they would not be in\ntheir place.\n\n\n## RELATION TO GENERAL PHYSICS.\n\n\n\n737.\n\nThe state in which general physics now is, appears, again, particularly\nfavourable to our labours; for natural philosophy, owing to\nindefatigable and variously directed research, has gradually attained\nsuch eminence, that it appears not impossible to refer a boundless\nempiricism to one centre.\n\n738.\n\nWithout referring to subjects which are too far removed from our own\nprovince, we observe that the formulæ under which the elementary\nappearances of nature are expressed, altogether tend in this direction;\nand it is easy to see that through this correspondence of expression, a\ncorrespondence in meaning will necessarily be soon arrived at.\n\n739.\n\nTrue observers of nature, however they may differ in opinion in other\nrespects, will agree that all which presents itself as appearance, all\nthat we meet with as phenomenon, must either indicate an original\ndivision which is capable of union, or an original unity which admits\nof division, and that the phenomenon will present itself accordingly.\nTo divide the united, to unite the divided, is the life of nature;\nthis is the eternal systole and diastole, the eternal collapsion and\nexpansion, the inspiration and expiration of the world in which we live\nand move.\n\n740.\n\nIt is hardly necessary to observe that what we here express as number\nand restrict to dualism is to be understood in a higher sense; the\nappearance of a third, a fourth order of facts progressively developing\nthemselves is to be similarly understood; but actual observation\nshould, above all, be the basis of all these expressions.\n\n741.\n\nIron is known to us as a peculiar substance, different from other\nsubstances: in its ordinary state we look upon it as a mere material\nremarkable only on account of its fitness for various uses and\napplications. How little, however, is necessary to do away with the\ncomparative insignificancy of this substance. A two-fold power is\ncalled forth,[1] which, while it tends again to a state of union, and,\nas it were, seeks itself, acquires a kind of magical relation with\nits like, and propagates this double property, which is in fact but a\nprinciple of reunion, throughout all bodies of the same kind. We here\nfirst observe the mere substance, iron; we see the division that takes\nplace in it propagate itself and disappear, and again easily become\nre-excited. This, according to our mode of thinking, is a primordial\nphenomenon in immediate relation with its idea, and which acknowledges\nnothing earthly beyond it.\n\n742.\n\nElectricity is again peculiarly characterised. As a mere quality we are\nunacquainted with it; for us it is a nothing, a zero, a mere point,\nwhich, however, dwells in all apparent existences, and at the same time\nis the point of origin whence, on the slightest stimulus, a double\nappearance presents itself, an appearance which only manifests itself\nto vanish. The conditions under which this manifestation is excited\nare infinitely varied, according to the nature of particular bodies.\nFrom the rudest mechanical friction of very different substances with\none another, to the mere contiguity of two entirely similar bodies,\nthe phenomenon is present and stirring, nay, striking and powerful,\nand so decided and specific, that when we employ the terms or formulæ\npolarity, plus and minus, for north and south, for glass and resin, we\ndo so justifiably and in conformity with nature.\n\n743.\n\nThis phenomenon, although it especially affects the surface, is yet by\nno means superficial. It influences the tendency or determination of\nmaterial qualities, and connects itself in immediate co-operation with\nthe important double phenomenon which takes place so universally in\nchemistry,--oxydation, and de-oxydation.\n\n744.\n\nTo introduce and include the appearances of colour in this series,\nthis circle of phenomena was the object of our labours. What we have\nnot succeeded in others will accomplish. We found a primordial vast\ncontrast between light and darkness, which may be more generally\nexpressed by light and its absence. We looked for the intermediate\nstate, and sought by means of it to compose the visible world of light,\nshade, and colour. In the prosecution of this we employed various terms\napplicable to the development of the phenomena, terms which we adopted\nfrom the theories of magnetism, of electricity, and of chemistry. It\nwas necessary, however, to extend this terminology, since we found\nourselves in an abstract region, and had to express more complicated\nrelations.\n\n745.\n\nIf electricity and galvanism, in their general character, are\ndistinguished as superior to the more limited exhibition of magnetic\nphenomena, it may be said that colour, although coming under similar\nlaws, is still superior; for since it addresses itself to the noble\nsense of vision, its perfections are more generally displayed. Compare\nthe varied effects which result from the augmentation of yellow and\nblue to red, from the combination of these two higher extremes to pure\nred, and the union of the two inferior extremes to green. What a far\nmore varied scheme is apparent here than that in which magnetism and\nelectricity are comprehended. These last phenomena may be said to be\ninferior again on another account; for though they penetrate and give\nlife to the universe, they cannot address themselves to man in a higher\nsense in order to his employing them æsthetically. The general, simple,\nphysical law must first be elevated and diversified itself in order to\nbe available for elevated uses.\n\n746.\n\nIf the reader, in this spirit, recalls what has been stated by us\nthroughout, generally and in detail, with regard to colour, he will\nhimself pursue and unfold what has been here only lightly hinted at.\nHe will augur well for science, technical processes, and art, if it\nshould prove possible to rescue the attractive subject of the doctrine\nof colours from the atomic restriction and isolation in which it has\nbeen banished, in order to restore it to the general dynamic flow of\nlife and action which the present age loves to recognise in nature.\nThese considerations will press upon us more strongly when, in the\nhistorical portion, we shall have to speak of many an enterprising\nand intelligent man who failed to possess his contemporaries with his\nconvictions.\n\n\n## RELATION TO THE THEORY OF MUSIC.\n\n\n\n747.\n\nBefore we proceed to the moral associations of colour, and the æsthetic\ninfluences arising from them, we have here to say a few words on its\nrelation to melody. That a certain relation exists between the two,\nhas been always felt; this is proved by the frequent comparisons we\nmeet with, sometimes as passing allusions, sometimes as circumstantial\nparallels. The error which writers have fallen into in trying to\nestablish this analogy we would thus define:\n\n748.\n\nColour and sound do not admit of being directly compared together\nin any way, but both are referable to a higher formula, both are\nderivable, although each for itself, from this higher law. They are\nlike two rivers which have their source in one and the same mountain,\nbut subsequently pursue their way under totally different conditions\nin two totally different regions, so that throughout the whole course\nof both no two points can be compared. Both are general, elementary\neffects acting according to the general law of separation and tendency\nto union, of undulation and oscillation, yet acting thus in wholly\ndifferent provinces, in different modes, on different elementary\nmediums, for different senses.--Note B B.\n\n749.\n\nCould some investigator rightly adopt the method in which we have\nconnected the doctrine of colours with natural philosophy generally,\nand happily supply what has escaped or been missed by us, the theory\nof sound, we are persuaded, might be perfectly connected with general\nphysics: at present it stands, as it were, isolated within the circle\nof science.\n\n750.\n\nIt is true it would be an undertaking of the greatest difficulty\nto do away with the positive character which we are now accustomed\nto attribute to music--a character resulting from the achievements\nof practical skill, from accidental, mathematical, æsthetical\ninfluences--and to substitute for all this a merely physical inquiry\ntending to resolve the science into its first elements. Yet considering\nthe point at which science and art are now arrived, considering the\nmany excellent preparatory investigations that have been made relative\nto this subject, we may perhaps still see it accomplished.\n\n\n## CONCLUDING OBSERVATIONS ON TERMINOLOGY.\n\n\n\n751.\n\nWe never sufficiently reflect that a language, strictly speaking, can\nonly be symbolical and figurative, that it can never express things\ndirectly, but only, as it were, reflectedly. This is especially the\ncase in speaking of qualities which are only imperfectly presented\nto observation, which might rather be called powers than objects,\nand which are ever in movement throughout nature. They are not to be\narrested, and yet we find it necessary to describe them; hence we look\nfor all kinds of formulæ in order, figuratively at least, to define\nthem.\n\n752.\n\nMetaphysical formulæ have breadth as well as depth, but on this\nvery account they require a corresponding import; the danger\nhere is vagueness. Mathematical expressions may in many cases be\nvery conveniently and happily employed, but there is always an\ninflexibility in them, and we presently feel their inadequacy; for even\nin elementary cases we are very soon conscious of an incommensurable\nidea; they are, besides, only intelligible to those who are especially\nconversant in the sciences to which such formulæ are appropriated. The\nterms of the science of mechanics are more addressed to the ordinary\nmind, but they are ordinary in other senses, and always have something\nunpolished; they destroy the inward life to offer from without an\ninsufficient substitute for it. The formulæ of the corpuscular theories\nare nearly allied to the last; through them the mutable becomes rigid,\ndescription and expression uncouth: while, again, moral terms, which\nundoubtedly can express nicer relations, have the effect of mere\nsymbols in the end, and are in danger of being lost in a play of wit.\n\n753.\n\nIf, however, a writer could use all these modes of description and\nexpression with perfect command, and thus give forth the result of his\nobservations on the phenomena of nature in a diversified language;\nif he could preserve himself from predilections, still embodying a\nlively meaning in as animated an expression, we might look for much\ninstruction communicated in the most agreeable of forms.\n\n754.\n\nYet, how difficult it is to avoid substituting the sign for the thing;\nhow difficult to keep the essential quality still living before us,\nand not to kill it with the word. With all this, we are exposed in\nmodern times to a still greater danger by adopting expressions and\nterminologies from all branches of knowledge and science to embody our\nviews of simple nature. Astronomy, cosmology, geology, natural history,\nnay religion and mysticism, are called in in aid; and how often do\nwe not find a general idea and an elementary state rather hidden and\nobscured than elucidated and brought nearer to us by the employment of\nterms, the application of which is strictly specific and secondary.\nWe are quite aware of the necessity which led to the introduction and\ngeneral adoption of such a language, we also know that it has become in\na certain sense indispensable; but it is only a moderate, unpretending\nrecourse to it, with an internal conviction of its fitness, that can\nrecommend it.\n\n755.\n\nAfter all, the most desirable principle would be that writers should\nborrow the expressions employed to describe the details of a given\nprovince of investigation from the province itself; treating the\nsimplest phenomenon as an elementary formula, and deriving and\ndeveloping the more complicated designations from this.\n\n756.\n\nThe necessity and suitableness of such a conventional language where\nthe elementary sign expresses the appearance itself, has been duly\nappreciated by extending, for instance, the application of the term\npolarity, which is borrowed from the magnet to electricity, &c. The\n_plus_ and _minus_ which may be substituted for this, have found as\nsuitable an application to many phenomena; even the musician, probably\nwithout troubling himself about these other departments, has been\nnaturally led to express the leading difference in the modes of melody\nby _major_ and _minor_.\n\n757.\n\nFor ourselves we have long wished to introduce the term polarity into\nthe doctrine of colours; with what right and in what sense, the present\nwork may show. Perhaps we may hereafter find room to connect the\nelementary phenomena together according to our mode, by a similar use\nof symbolical terms, terms which must at all times convey the directly\ncorresponding idea; we shall thus render more explicit what has been\nhere only alluded to generally, and perhaps too vaguely expressed.\n\n\n[1] Eine Entzweyung geht vor; literally, _a division takes place_.\nAccording to some, the two magnetic powers are previously in the bar,\nand are then separated at the ends.--T.\n\n\n\n\n## PART VI.\n\n\n\n## EFFECT OF COLOUR WITH REFERENCE TO MORAL ASSOCIATIONS.\n\n\n\n758.\n\nSince colour occupies so important a place in the series of elementary\nphenomena, filling as it does the limited circle assigned to it with\nfullest variety, we shall not be surprised to find that its effects are\nat all times decided and significant, and that they are immediately\nassociated with the emotions of the mind. We shall not be surprised\nto find that these appearances presented singly, are specific, that\nin combination they may produce an harmonious, characteristic, often\neven an inharmonious effect on the eye, by means of which they act on\nthe mind; producing this impression in their most general elementary\ncharacter, without relation to the nature or form of the object on\nwhose surface they are apparent. Hence, colour considered as an element\nof art, may be made subservient to the highest æsthetical ends.--Note C\nC.\n\n759.\n\nPeople experience a great delight in colour, generally. The eye\nrequires it as much as it requires light. We have only to remember\nthe refreshing sensation we experience, if on a cloudy day the sun\nillumines a single portion of the scene before us and displays its\ncolours. That healing powers were ascribed to coloured gems, may have\narisen from the experience of this indefinable pleasure.\n\n760.\n\nThe colours which we see on objects are not qualities entirely\nstrange to the eye; the organ is not thus merely habituated to the\nimpression; no, it is always predisposed to produce colour of itself,\nand experiences a sensation of delight if something analogous to its\nown nature is offered to it from without; if its susceptibility is\ndistinctly determined towards a given state.\n\n761.\n\nFrom some of our earlier observations we can conclude, that general\nimpressions produced by single colours cannot be changed, that they act\nspecifically, and must produce definite, specific states in the living\norgan.\n\n762.\n\nThey likewise produce a corresponding influence on the mind. Experience\nteaches us that particular colours excite particular states of feeling.\nIt is related of a witty Frenchman, \"Il prétendoit que son ton de\nconversation avec Madame étoit changé depuis qu'elle avoit changé en\ncramoisi le meuble de son cabinet, qui étoit bleu.\"\n\n763.\n\nIn order to experience these influences completely, the eye should be\nentirely surrounded with one colour; we should be in a room of one\ncolour, or look through a coloured glass. We are then identified with\nthe hue, it attunes the eye and mind in mere unison with itself.\n\n764.\n\nThe colours on the _plus_ side are yellow, red-yellow (orange),\nyellow-red (minium, cinnabar). The feelings they excite are quick,\nlively, aspiring.\n\n\n## YELLOW.\n\n\n\n765.\n\nThis is the colour nearest the light. It appears on the slightest\nmitigation of light, whether by semi-transparent mediums or faint\nreflection from white surfaces. In prismatic experiments it extends\nitself alone and widely in the light space, and while the two poles\nremain separated from each other, before it mixes with blue to\nproduce green it is to be seen in its utmost purity and beauty. How\nthe chemical yellow developes itself in and upon the white, has been\ncircumstantially described in its proper place.\n\n766.\n\nIn its highest purity it always carries with it the nature of\nbrightness, and has a serene, gay, softly exciting character.\n\n767.\n\nIn this state, applied to dress, hangings, carpeting, &c., it is\nagreeable. Gold in its perfectly unmixed state, especially when the\neffect of polish is superadded, gives us a new and high idea of this\ncolour; in like manner, a strong yellow, as it appears on satin, has a\nmagnificent and noble effect.\n\n768.\n\nWe find from experience, again, that yellow excites a warm and\nagreeable impression. Hence in painting it belongs to the illumined and\nemphatic side.\n\n769.\n\nThis impression of warmth may be experienced in a very lively manner if\nwe look at a landscape through a yellow glass, particularly on a grey\nwinter's day. The eye is gladdened, the heart expanded and cheered, a\nglow seems at once to breathe towards us.\n\n770.\n\nIf, however, this colour in its pure and bright state is agreeable\nand gladdening, and in its utmost power is serene and noble, it is, on\nthe other hand, extremely liable to contamination, and produces a very\ndisagreeable effect if it is sullied, or in some degree tends to the\n_minus_ side. Thus, the colour of sulphur, which inclines to green, has\na something unpleasant in it.\n\n771.\n\nWhen a yellow colour is communicated to dull and coarse surfaces,\nsuch as common cloth, felt, or the like, on which it does not appear\nwith full energy, the disagreeable effect alluded to is apparent. By\na slight and scarcely perceptible change, the beautiful impression\nof fire and gold is transformed into one not undeserving the epithet\nfoul; and the colour of honour and joy reversed to that of ignominy\nand aversion. To this impression the yellow hats of bankrupts and the\nyellow circles on the mantles of Jews, may have owed their origin.\n\n\n## RED-YELLOW.\n\n\n\n772.\n\nAs no colour can be considered as stationary, so we can very easily\naugment yellow into reddish by condensing or darkening it. The colour\nincreases in energy, and appears in red-yellow more powerful and\nsplendid.\n\n773.\n\nAll that we have said of yellow is applicable here in a higher\ndegree. The red-yellow gives an impression of warmth and gladness,\nsince it represents the hue of the intenser glow of fire, and of the\nmilder radiance of the setting sun. Hence it is agreeable around us,\nand again, as clothing, in greater or less degrees is cheerful and\nmagnificent. A slight tendency to red immediately gives a new character\nto yellow, and while the English and Germans content themselves\nwith bright pale yellow colours in leather, the French, as Castel\nhas remarked, prefer a yellow enhanced to red; indeed, in general,\neverything in colour is agreeable to them which belongs to the active\nside.\n\n\n## YELLOW-RED.\n\n\n\n774.\n\nAs pure yellow passes very easily to red-yellow, so the deepening of\nthis last to yellow-red is not to be arrested. The agreeable, cheerful\nsensation which red-yellow excites, increases to an intolerably\npowerful impression in bright yellow-red.\n\n775,\n\nThe active side is here in its highest energy, and it is not to\nbe wondered at that impetuous, robust, uneducated men, should be\nespecially pleased with this colour. Among savage nations the\ninclination for it has been universally remarked, and when children,\nleft to themselves, begin to use tints, they never spare vermilion and\nminium.\n\n776.\n\nIn looking steadfastly at a perfectly yellow-red surface, the colour\nseems actually to penetrate the organ. It produces an extreme\nexcitement, and still acts thus when somewhat darkened. A yellow-red\ncloth disturbs and enrages animals. I have known men of education to\nwhom its effect was intolerable if they chanced to see a person dressed\nin a scarlet cloak on a grey, cloudy day.\n\n777.\n\nThe colours on the _minus_ side are blue, red-blue, and blue-red. They\nproduce a restless, susceptible, anxious impression.\n\n\n## BLUE.\n\n\n\n778.\n\nAs yellow is always accompanied with light, so it may be said that blue\nstill brings a principle of darkness with it.\n\n779.\n\nThis colour has a peculiar and almost indescribable effect on the eye.\nAs a hue it is powerful, but it is on the negative side, and in its\nhighest purity is, as it were, a stimulating negation. Its appearance,\nthen, is a kind of contradiction between excitement and repose.\n\n780.\n\nAs the upper sky and distant mountains appear blue, so a blue surface\nseems to retire from us.\n\n781.\n\nBut as we readily follow an agreeable object that flies from us, so we\nlove to contemplate blue, not because it advances to us, but because it\ndraws us after it.\n\n782.\n\nBlue gives us an impression of cold, and thus, again, reminds us of\nshade. We have before spoken of its affinity with black.\n\n783.\n\nRooms which are hung with pure blue, appear in some degree larger, but\nat the same time empty and cold.\n\n784.\n\nThe appearance of objects seen through a blue glass is gloomy and\nmelancholy.\n\n785.\n\nWhen blue partakes in some degree of the _plus_ side, the effect is not\ndisagreeable. Sea-green is rather a pleasing colour.\n\n\n## RED-BLUE.\n\n\n\n786.\n\nWe found yellow very soon tending to the intense state, and we observe\nthe same progression in blue.\n\n787.\n\nBlue deepens very mildly into red, and thus acquires a somewhat active\ncharacter, although it is on the passive side. Its exciting power is,\nhowever, of a very different kind from that of the red-yellow. It may\nbe said to disturb rather than enliven.\n\n788.\n\nAs augmentation itself is not to be arrested, so we feel an inclination\nto follow the progress of the colour, not, however, as in the case of\nthe red-yellow, to see it still increase in the active sense, but to\nfind a point to rest in.\n\n789.\n\nIn a very attenuated state, this colour is known to us under the name\nof lilac; but even in this degree it has a something lively without\ngladness.\n\n790.\n\nThis unquiet feeling increases as the hue progresses, and it may be\nsafely assumed, that a carpet of a perfectly pure deep blue-red would\nbe intolerable. On this account, when it is used for dress, ribbons, or\nother ornaments, it is employed in a very attenuated and light state,\nand thus displays its character as above defined, in a peculiarly\nattractive manner.\n\n791.\n\nAs the higher dignitaries of the church have appropriated this unquiet\ncolour to themselves, we may venture to say that it unceasingly aspires\nto the cardinal's red through the restless degrees of a still impatient\nprogression.\n\n\nRED.\n\n\n792.\n\nWe are here to forget everything that borders on yellow or blue. We\nare to imagine an absolutely pure red, like fine carmine suffered to\ndry on white porcelain. We have called this colour \"purpur\" by way\nof distinction, although we are quite aware that the purple of the\nancients inclined more to blue.\n\n793.\n\nWhoever is acquainted with the prismatic origin of red, will not think\nit paradoxical if we assert that this colour partly _actu_, partly\n_potentiâ_, includes all the other colours.\n\n794.\n\nWe have remarked a constant progress or augmentation in yellow and\nblue, and seen what impressions were produced by the various states;\nhence it may naturally be inferred that now, in the junction of the\ndeepened extremes, a feeling of satisfaction must succeed; and thus, in\nphysical phenomena, this highest of all appearances of colour arises\nfrom the junction of two contrasted extremes which have gradually\nprepared themselves for a union.\n\n795.\n\nAs a pigment, on the other hand, it presents itself to us already\nformed, and is most perfect as a hue in cochineal; a substance which,\nhowever, by chemical action may be made to tend to the _plus_ or the\n_minus_ side, and may be considered to have attained the central point\nin the best carmine.\n\n796.\n\nThe effect of this colour is as peculiar as its nature. It conveys an\nimpression of gravity and dignity, and at the same time of grace and\nattractiveness. The first in its dark deep state, the latter in its\nlight attenuated tint; and thus the dignity of age and the amiableness\nof youth may adorn itself with degrees of the same hue.\n\n797.\n\nHistory relates many instances of the jealousy of sovereigns with\nregard to the quality of red. Surrounding accompaniments of this colour\nhave always a grave and magnificent effect.\n\n798.\n\nThe red glass exhibits a bright landscape in so dreadful a hue as to\ninspire sentiments of awe.\n\n799.\n\nKermes and cochineal, the two materials chiefly employed in dyeing to\nproduce this colour, incline more or less to the _plus_ or _minus_\nstate, and may be made to pass and repass the culminating point by\nthe action of acids and alkalis: it is to be observed that the French\narrest their operations on the active side, as is proved by the French\nscarlet, which inclines to yellow. The Italians, on the other hand,\nremain on the passive side, for their scarlet has a tinge of blue.\n\n800.\n\nBy means of a similar alkaline treatment, the so-called crimson is\nproduced; a colour which the French must be particularly prejudiced\nagainst, since they employ the expressions--\"Sot en cramoisi, méchant\nen cramoisi,\" to mark the extreme of the silly and the reprehensible.\n\n\n## GREEN.\n\n\n\n801.\n\nIf yellow and blue, which we consider as the most fundamental and\nsimple colours, are united as they first appear, in the first state of\ntheir action, the colour which we call green is the result.\n\n802.\n\nThe eye experiences a distinctly grateful impression from this colour.\nIf the two elementary colours are mixed in perfect equality so that\nneither predominates, the eye and the mind repose on the result of this\njunction as upon a simple colour. The beholder has neither the wish\nnor the power to imagine a state beyond it. Hence for rooms to live in\nconstantly, the green colour is most generally selected.\n\n\n## COMPLETENESS AND HARMONY.\n\n\n\n803.\n\nWe have hitherto assumed, for the sake of clearer explanation, that the\neye can be compelled to assimilate or identify itself with a single\ncolour; but this can only be possible for an instant.\n\n804.\n\nFor when we find ourselves surrounded by a given colour which excites\nits corresponding sensation on the eye, and compels us by its presence\nto remain in a state identical with it, this state is soon found to be\nforced, and the organ unwillingly remains in it.\n\n805.\n\nWhen the eye sees a colour it is immediately excited, and it is its\nnature, spontaneously and of necessity, at once to produce another,\nwhich with the original colour comprehends the whole chromatic scale.\nA single colour excites, by a specific sensation, the tendency to\nuniversality.\n\n806.\n\nTo experience this completeness, to satisfy itself, the eye seeks for\na colourless space next every hue in order to produce the complemental\nhue upon it.\n\n807.\n\nIn this resides the fundamental law of all harmony of colours, of which\nevery one may convince himself by making himself accurately acquainted\nwith the experiments which we have described in the chapter on the\nphysiological colours.\n\n808.\n\nIf, again, the entire scale is presented to the eye externally, the\nimpression is gladdening, since the result of its own operation is\npresented to it in reality. We turn our attention therefore, in the\nfirst place, to this harmonious juxtaposition.\n\n809.\n\nAs a very simple means of comprehending the principle of this, the\nreader has only to imagine a moveable diametrical index in the\ncolorific circle.[1] The index, as it revolves round the whole circle,\nindicates at its two extremes the complemental colours, which, after\nall, may be reduced to three contrasts.\n\n810.\n\nYellow demands Red-blue,\nBlue   demands Red-yellow,\nRed    demands Green,\nand contrariwise.\n\n811.\n\nIn proportion as one end of the supposed index deviates from the\ncentral intensity of the colours, arranged as they are in the natural\norder, so the opposite end changes its place in the contrasted\ngradation, and by such a simple contrivance the complemental colours\nmay be indicated at any given point. A chromatic circle might be made\nfor this purpose, not confined, like our own, to the leading colours,\nbut exhibiting them with their transitions in an unbroken series.\nThis would not be without its use, for we are here considering a very\nimportant point which deserves all our attention.[2]\n\n812.\n\nWe before stated that the eye could be in some degree pathologically\naffected by being long confined to a single colour; that, again,\ndefinite moral impressions were thus produced, at one time lively and\naspiring, at another susceptible and anxious--now exalted to grand\nassociations, now reduced to ordinary ones. We now observe that the\ndemand for completeness, which is inherent in the organ, frees us from\nthis restraint; the eye relieves itself by producing the opposite\nof the single colour forced upon it, and thus attains the entire\nimpression which is so satisfactory to it.\n\n813.\n\nSimple, therefore, as these strictly harmonious contrasts are, as\npresented to us in the narrow circle, the hint is important, that\nnature tends to emancipate the sense from confined impressions by\nsuggesting and producing the whole, and that in this instance we have a\nnatural phenomenon immediately applicable to æsthetic purposes.\n\n814.\n\nWhile, therefore, we may assert that the chromatic scale, as given by\nus, produces an agreeable impression by its ingredient hues, we may\nhere remark that those have been mistaken who have hitherto adduced\nthe rainbow as an example of the entire scale; for the chief colour,\npure red, is deficient in it, and cannot be produced, since in this\nphenomenon, as well as in the ordinary prismatic series, the yellow-red\nand blue-red cannot attain to a union.\n\n815.\n\nNature perhaps exhibits no general phenomenon where the scale is in\ncomplete combination. By artificial experiments such an appearance may\nbe produced in its perfect splendour. The mode, however, in which the\nentire series is connected in a circle, is rendered most intelligible\nby tints on paper, till after much experience and practice, aided by\ndue susceptibility of the organ, we become penetrated with the idea of\nthis harmony, and feel it present in our minds.\n\n816.\n\nBesides these pure, harmonious, self-developed combinations, which\nalways carry the conditions of completeness with them, there are\nothers which may be arbitrarily produced, and which may be most easily\ndescribed by observing that they are to be found in the colorific\ncircle, not by diameters, but by chords, in such a manner that an\nintermediate colour is passed over.\n\n817.\n\nWe call these combinations characteristic because they have all a\ncertain significancy and tend to excite a definite impression; an\nimpression, however, which does not altogether satisfy, inasmuch as\nevery characteristic quality of necessity presents itself only as a\npart of a whole, with which it has a relation, but into which it cannot\nbe resolved.\n\n818.\n\nAs we are acquainted with the impressions produced by the colours\nsingly as well as in their harmonious relations, we may at once\nconclude that the character of the arbitrary combinations will be very\ndifferent from each other as regards their significancy. We proceed to\nreview them separately.\n\n\n## YELLOW AND BLUE.\n\n\n\n819.\n\nThis is the simplest of such combinations. It may be said that it\ncontains too little, for since every trace of red is wanting in it,\nit is defective as compared with the whole scale. In this view it\nmay be called poor, and as the two contrasting elements are in their\nlowest state, may be said to be ordinary; yet it is recommended by\nits proximity to green--in short, by containing the ingredients of an\nultimate state.\n\n\n## YELLOW AND RED.\n\n\n\n820.\n\nThis is a somewhat preponderating combination, but it has a serene\nand magnificent effect. The two extremes of the active side are seen\ntogether without conveying any idea of progression from one to the\nother. As the result of their combination in pigments is yellow-red, so\nthey in some degree represent this colour.\n\n\n## BLUE AND RED.\n\n\n\n821.\n\nThe two ends of the passive side, with the excess of the upper end of\nthe active side. The effect of this juxtaposition approaches that of\nthe blue-red produced by their union.\n\n\n## YELLOW-RED AND BLUE-RED.\n\n\n\n822.\n\nThese, when placed together, as the deepened extremes of both sides,\nhave something exciting, elevated: they give us a presentiment of red,\nwhich in physical experiments is produced by their union.\n\n823.\n\nThese four combinations have also the common quality of producing the\nintermediate colour of our colorific circle by their union, a union\nwhich actually takes place if they are opposed to each other in small\nquantities and seen from a distance. A surface covered with narrow blue\nand yellow stripes appears green at a certain distance.\n\n824.\n\nIf, again, the eye sees blue and yellow next each other, it finds\nitself in a peculiar disposition to produce green without accomplishing\nit, while it neither experiences a satisfactory sensation in\ncontemplating the detached colours, nor an impression of completeness\nin the two.\n\n825.\n\nThus it will be seen that it was not without reason we called these\ncombinations characteristic; the more so, since the character of each\ncombination must have a relation to that of the single colours of which\nit consists.\n\n\n## COMBINATIONS NON-CHARACTERISTIC.\n\n\n\n826.\n\nWe now turn our attention to the last kind of combinations. These are\neasily found in the circle; they are indicated by shorter chords, for\nin this case we do not pass over an entire intermediate colour, but\nonly the transition from one to the other.\n\n827.\n\nThese combinations may justly be called non-characteristic, inasmuch\nas the colours are too nearly alike for their impression to be\nsignificant. Yet most of these recommend themselves to a certain\ndegree, since they indicate a progressive state, though its relations\ncan hardly be appreciable.\n\n828.\n\nThus yellow and yellow-red, yellow-red and red, blue and blue-red,\nblue-red and red, represent the nearest degrees of augmentation and\nculmination, and in certain relations as to quantity may produce no\nunpleasant effect.\n\n829.\n\nThe juxtaposition of yellow and green has always something ordinary,\nbut in a cheerful sense; blue and green, on the other hand, is ordinary\nin a repulsive sense. Our good forefathers called these last fool's\ncolours.\n\n\n## RELATION OF THE COMBINATIONS TO LIGHT AND DARK.\n\n\n\n830.\n\nThese combinations may be very much varied by making both colours light\nor both dark, or one light and the other dark; in which modifications,\nhowever, all that has been found true in a general sense is applicable\nto each particular case. With regard to the infinite variety thus\nproduced, we merely observe:\n\n831.\n\nThe colours of the active side placed next to black gain in energy,\nthose of the passive side lose. The active conjoined with white and\nbrightness lose in strength, the passive gain in cheerfulness. Red and\ngreen with black appear dark and grave; with white they appear gay.\n\n832.\n\nTo this we may add that all colours may be more or less broken or\nneutralised, may to a certain degree be rendered nameless, and thus\ncombined partly together and partly with pure colours; but although the\nrelations may thus be varied to infinity, still all that is applicable\nwith regard to the pure colours will be applicable in these cases.\n\n\n## CONSIDERATIONS DERIVED FROM THE EVIDENCE OF EXPERIENCE AND HISTORY.\n\n\n\n833.\n\nThe principles of the harmony of colours having been thus far defined,\nit may not be irrelevant to review what has been adduced in connexion\nwith experience and historical examples.\n\n834.\n\nThe principles in question have been derived from the constitution of\nour nature and the constant relations which are found to obtain in\nchromatic phenomena. In experience we find much that is in conformity\nwith these principles, and much that is opposed to them.\n\n835.\n\nMen in a state of nature, uncivilised nations, children, have a great\nfondness for colours in their utmost brightness, and especially for\nyellow-red: they are also pleased with the motley. By this expression\nwe understand the juxtaposition of vivid colours without an harmonious\nbalance; but if this balance is observed, through instinct or accident,\nan agreeable effect may be produced. I remember a Hessian officer,\nreturned from America, who had painted his face with the positive\ncolours, in the manner of the Indians; a kind of completeness or due\nbalance was thus produced, the effect of which was not disagreeable.\n\n836.\n\nThe inhabitants of the south of Europe make use of very brilliant\ncolours for their dresses. The circumstance of their procuring silk\nstuffs at a cheap rate is favourable to this propensity. The women,\nespecially, with their bright-coloured bodices and ribbons, are always\nin harmony with the scenery, since they cannot possibly surpass the\nsplendour of the sky and landscape.\n\n837.\n\nThe history of dyeing teaches us that certain technical conveniences\nand advantages have had great influence on the costume of nations.\nWe find that the Germans wear blue very generally because it is a\npermanent colour in cloth; so in many districts all the country people\nwear green twill, because that material takes a green dye well. If\na traveller were to pay attention to these circumstances, he might\ncollect some amusing and curious facts.\n\n838.\n\nColours, as connected with particular frames of mind, are again a\nconsequence of peculiar character and circumstances. Lively nations,\nthe French for instance, love intense colours, especially on the active\nside; sedate nations, like the English and Germans, wear straw-coloured\nor leather-coloured yellow accompanied with dark blue. Nations aiming\nat dignity of appearance, the Spaniards and Italians for instance,\nsuffer the red colour of their mantles to incline to the passive side.\n\n839.\n\nIn dress we associate the character of the colour with the character of\nthe person. We may thus observe the relation of colours singly, and in\ncombination, to the colour of the complexion, age, and station.\n\n840.\n\nThe female sex in youth is attached to rose-colour and sea-green, in\nage to violet and dark-green. The fair-haired prefer violet, as opposed\nto light yellow, the brunettes, blue, as opposed to yellow-red, and\nall on good grounds. The Roman emperors were extremely jealous with\nregard to their purple. The robe of the Chinese Emperor is orange\nembroidered with red; his attendants and the ministers of religion wear\ncitron-yellow.\n\n841.\n\nPeople of refinement have a disinclination to colours. This may be\nowing partly to weakness of sight, partly to the uncertainty of taste,\nwhich readily takes refuge in absolute negation. Women now appear\nalmost universally in white and men in black.\n\n842.\n\nAn observation, very generally applicable, may not be out of place\nhere, namely, that man, desirous as he is of being distinguished, is\nquite as willing to be lost among his fellows.\n\n843.\n\nBlack was intended to remind the Venetian noblemen of republican\nequality.\n\n844.\n\nTo what degree the cloudy sky of northern climates may have gradually\nbanished colour may also admit of explanation.\n\n845.\n\nThe scale of positive colours is obviously soon exhausted; on the\nother hand, the neutral, subdued, so-called fashionable colours\npresent infinitely varying degrees and shades, most of which are not\nunpleasing.\n\n846.\n\nIt is also to be remarked that ladies, in wearing positive colours,\nare in danger of making a complexion which may not be very bright\nstill less so, and thus to preserve a due balance with such brilliant\naccompaniments, they are induced to heighten their complexions\nartificially.\n\n847.\n\nAn amusing inquiry might be made which would lead to a critique of\nuniforms, liveries, cockades, and other distinctions, according to the\nprinciples above hinted at. It might be observed, generally, that such\ndresses and insignia should not be composed of harmonious colours.\nUniforms should be characteristic and dignified; liveries might be\nordinary and striking to the eye. Examples both good and bad would\nnot be wanting, since the scale of colours usually employed for such\npurposes is limited, and its varieties have been often enough tried.[3]\n\n\nÆSTHETIC INFLUENCE.\n\n\n848.\n\nFrom the moral associations connected with the appearance of colours,\nsingle or combined, their æsthetic influence may now be deduced for\nthe artist. We shall touch the most essential points to be attended\nto after first considering the general condition of pictorial\nrepresentation, light and shade, with which the appearance of colour is\nimmediately connected.\n\n\n## CHIARO-SCURO.\n\n\n\n849.\n\nWe apply the term chiaro-scuro (Helldunkel) to the appearance of\nmaterial objects when the mere effect produced on them by light and\nshade is considered.--Note D D.\n\n850.\n\nIn a narrower sense a mass of shadow lighted by reflexes is often\nthus designated; but we here use the expression in its first and more\ngeneral sense.\n\n851.\n\nThe separation of light and dark from all appearance of colour is\npossible and necessary. The artist will solve the mystery of imitation\nsooner by first considering light and dark independently of colour, and\nmaking himself acquainted with it in its whole extent.\n\n852.\n\nChiaro-scuro exhibits the substance as substance, inasmuch as light and\nshade inform us as to degrees of density.\n\n853.\n\nWe have here to consider the highest light, the middle tint, and the\nshadow, and in the last the shadow of the object itself, the shadow it\ncasts on other objects, and the illumined shadow or reflexion.\n\n854.\n\nThe globe is well adapted for the general exemplification of the nature\nof chiaro-scuro, but it is not altogether sufficient. The softened\nunity of such complete rotundity tends to the vapoury, and in order to\nserve as a principle for effects of art, it should be composed of plane\nsurfaces, so as to define the gradations more.\n\n855.\n\nThe Italians call this manner \"il piazzoso;\" in German it might\nbe called \"das Flächenhafte.\"[4] If, therefore, the sphere is a\nperfect example of natural chiaro-scuro, a polygon would exhibit the\nartist-like treatment in which all kinds of lights, half-lights,\nshadows, and reflexions, would be appreciable.--Note E E.\n\n856.\n\nThe bunch of grapes is recognised as a good example of a picturesque\ncompleteness in chiaro-scuro, the more so as it is fitted, from its\nform, to represent a principal group; but it is only available for the\nmaster who can see in it what he has the power of producing.\n\n857.\n\nIn order to make the first idea intelligible to the beginner, (for\nit is difficult to consider it abstractedly even in a polygon,) we\nmay take a cube, the three sides of which that are seen represent the\nlight, the middle tint, and the shadow in distinct order.\n\n858.\n\nTo proceed again to the chiaro-scuro of a more complicated figure, we\nmight select the example of an open book, which presents a greater\ndiversity.\n\n859.\n\nWe find the antique statues of the best time treated very much with\nreference to these effects. The parts intended to receive the light\nare wrought with simplicity, the portion originally in shade is, on\nthe other hand, in more distinct surfaces to make them susceptible\nof a variety of reflexions; here the example of the polygon will be\nremembered.--Note F F.\n\n860.\n\nThe pictures of Herculaneum and the Aldobrandini marriage are examples\nof antique painting in the same style.\n\n861.\n\nModern examples may be found in single figures by Raphael, in entire\nworks by Correggio, and also by the Flemish masters, especially Rubens.\n\n\n## TENDENCY TO COLOUR.\n\n\n\n862.\n\nA picture in black and white seldom makes its appearance; some works\nof Polidoro are examples of this kind of art. Such works, inasmuch as\nthey can attain form and keeping, are estimable, but they have little\nattraction for the eye, since their very existence supposes a violent\nabstraction.\n\n863.\n\nIf the artist abandons himself to his feeling, colour presently\nannounces itself. Black no sooner inclines to blue than the eye demands\nyellow, which the artist instinctively modifies, and introduces partly\npure in the light, partly reddened and subdued as brown, in the\nreflexes, thus enlivening the whole.--Note G G.\n\n864.\n\nAll kinds of _camayeu_, or colour on similar colour, end in the\nintroduction either of a complemental contrast, or some variety of hue.\nThus, Polidoro in his black and white frescoes sometimes introduced a\nyellow vase, or something of the kind.\n\n865.\n\nIn general it may be observed that men have at all times instinctively\nstriven after colour in the practice of the art. We need only observe\ndaily, how soon amateurs proceed from colourless to coloured materials.\nPaolo Uccello painted coloured landscapes to colourless figures.--Note\nH H.\n\n866.\n\nEven the sculpture of the ancients could not be exempt from the\ninfluence of this propensity. The Egyptians painted their bas-reliefs;\nstatues had eyes of coloured stones. Porphyry draperies were added to\nmarble heads and extremities, and variegated stalactites were used\nfor the pedestals of busts. The Jesuits did not fail to compose the\nstatue of their S. Luigi, in Rome, in this manner, and the most modern\nsculpture distinguishes the flesh from the drapery by staining the\nlatter.\n\n\n## KEEPING.\n\n\n\n867.\n\nIf linear perspective displays the gradation of objects in their\napparent size as affected by distance, aërial perspective shows us\ntheir gradation in greater or less distinctness, as affected by the\nsame cause.\n\n868.\n\nAlthough from the nature of the organ of sight, we cannot see distant\nobjects so distinctly as nearer ones, yet aërial perspective is\ngrounded strictly on the important fact that all mediums called\ntransparent are in some degree dim.\n\n869.\n\nThe atmosphere is thus always, more or less, semi-transparent. This\nquality is remarkable in southern climates, even when the barometer is\nhigh, the weather dry, and the sky cloudless, for a very pronounced\ngradation is observable between objects but little removed from each\nother.\n\n870.\n\nThe appearance on a large scale is known to every one; the painter,\nhowever, sees or believes he sees, the gradation in the slightest\nvarieties of distance. He exemplifies it practically by making a\ndistinction, for instance, in the features of a face according to their\nrelative position as regards the plane of the picture. The direction of\nthe light is attended to in like manner. This is considered to produce\na gradation from side to side, while keeping has reference to depth, to\nthe comparative distinctness of near and distant things.\n\n871.\n\nIn proceeding to consider this subject, we assume that the painter is\ngenerally acquainted with our sketch of the theory of colours, and that\nhe has made himself well acquainted with certain chapters and rubrics\nwhich especially concern him. He will thus be enabled to make use of\ntheory as well as practice in recognising the principles of effect in\nnature, and in employing the means of art.\n\n\n## COLOUR IN GENERAL NATURE.\n\n\n\n872.\n\nThe first indication of colour announces itself in nature together\nwith the gradations of aërial perspective; for aërial perspective is\nintimately connected with the doctrine of semi-transparent mediums. We\nsee the sky, distant objects and even comparatively near shadows, blue.\nAt the same moment, the illuminating and illuminated objects appear\nyellow, gradually deepening to red. In many cases the physiological\nsuggestion of contrasts comes into the account, and an entirely\ncolourless landscape, by means of these assisting and counteracting\ntendencies, appears to our eyes completely coloured.\n\n873.\n\nLocal colours are composed of the general elementary colours; but these\nare determined or specified according to the properties of substances\nand surfaces on which they appear: this specification is infinite.\n\n874.\n\nThus, there is at once a great difference between silk and wool\nsimilarly dyed. Every kind of preparation and texture produces\ncorresponding modifications. Roughness, smoothness, polish, all are to\nbe considered.\n\n875.\n\nIt is therefore one of the pernicious prejudices of art that the\nskilful painter must never attend to the material of draperies,\nbut always represent, as it were, only abstract folds. Is not all\ncharacteristic variety thus done away with, and is the portrait of Leo\nX. less excellent because velvet, satin, and moreen, are imitated in\ntheir relative effect?\n\n876.\n\nIn the productions of nature, colours appear more or less modified,\nspecified, even individualised: this may be readily observed in\nminerals and plants, in the feathers of birds and the skins of beasts.\n\n877.\n\nThe chief art of the painter is always to imitate the actual appearance\nof the definite hue, doing away with the recollection of the elementary\ningredients of colour. This difficulty is in no instance greater than\nin the imitation of the surface of the human figure.\n\n878.\n\nThe colour of flesh, as a whole, belongs to the active side, yet the\nbluish of the passive side mingles with it. The colour is altogether\nremoved from the elementary state and neutralised by organisation.\n\n879.\n\nTo bring the colouring of general nature into harmony with the\ncolouring of a given object, will perhaps be more attainable for the\njudicious artist after the consideration of what has been pointed out\nin the foregoing theory. For the most fancifully beautiful and varied\nappearances may still be made true to the principles of nature.\n\n\n## CHARACTERISTIC COLOURING.\n\n\n\n880.\n\nThe combination of coloured objects, as well as the colour of\ntheir ground, should depend on considerations which the artist\npre-establishes for himself. Here a reference to the effect of colours\nsingly or combined, on the feelings, is especially necessary. On this\naccount the painter should possess himself with the idea of the general\ndualism, as well as of particular contrasts, not forgetting what has\nbeen adverted to with regard to the qualities of colours.\n\n881.\n\nThe characteristic in colour may be comprehended under three leading\nrubrics, which we here define as the powerful, the soft, and the\nsplendid.\n\n882.\n\nThe first is produced by the preponderance of the active side, the\nsecond by that of the passive side, and the third by completeness, by\nthe exhibition of the whole chromatic scale in due balance.\n\n883.\n\nThe powerful impression is attained by yellow, yellow-red, and red,\nwhich last colour is to be arrested on the plus side. But little violet\nand blue, still less green, are admissible. The soft effect is produced\nby blue, violet, and red, which in this case is arrested on the minus\nside; a moderate addition of yellow and yellow-red, but much green may\nbe admitted.\n\n884.\n\nIf it is proposed to produce both these effects in their full\nsignificancy, the complemental colours may be excluded to a minimum,\nand only so much of them may be suffered to appear as is indispensable\nto convey an impression of completeness.\n\n\n## HARMONIOUS COLOURING.\n\n\n\n885.\n\nAlthough the two characteristic divisions as above defined may in some\nsense be also called harmonious, the harmonious effect, properly so\ncalled, only takes place when all the colours are exhibited together in\ndue balance.\n\n886.\n\nIn this way the splendid as well as the agreeable may be produced; both\nof these, however, have of necessity a certain generalised effect, and\nin this sense may be considered the reverse of the characteristic.\n\n887.\n\nThis is the reason why the colouring of most modern painters is without\ncharacter, for, while they follow their general instinctive feeling\nonly, the last result of such a tendency must be mere completeness;\nthis, they more or less attain, but thus at the same time neglect the\ncharacteristic impression which the subject might demand.\n\n888.\n\nBut if the principles before alluded to are kept in view, it must be\napparent that a distinct style of colour may be adopted on safe grounds\nfor every subject. The application requires, it is true, infinite\nmodifications, which can only succeed in the hands of genius.\n\n\n## GENUINE TONE.\n\n\n\n889.\n\nIf the word tone, or rather tune, is to be still borrowed in future\nfrom music, and applied to colouring, it might be used in a better\nsense than heretofore.\n\n890.\n\nFor it would not be unreasonable to compare a painting of powerful\neffect, with a piece of music in a sharp key; a painting of soft effect\nwith a piece of music in a flat key, while other equivalents might be\nfound for the modifications of these two leading modes.\n\n\n## FALSE TONE.\n\n\n\n891.\n\nThe word tone has been hitherto understood to mean a veil of a\nparticular colour spread over the whole picture; it was generally\nyellow, for the painter instinctively pushed the effect towards the\npowerful side.\n\n892.\n\nIf we look at a picture through a yellow glass it will appear in this\ntone. It is worth while to make this experiment again and again, in\norder to observe what takes place in such an operation. It is a sort of\nartificial light, deepening, and at the same time darkening the _plus_\nside, and neutralising the _minus_ side.\n\n893.\n\nThis spurious tone is produced instinctively through uncertainty\nas to the means of attaining a genuine effect; so that instead of\ncompleteness, monotony is the result.\n\n\n## WEAK COLOURING.\n\n\n\n894.\n\nIt is owing to the same uncertainty that the colours are sometimes so\nmuch broken as to have the effect of a grey camayeu, the handling being\nat the same time as delicate as possible.\n\n895.\n\nThe harmonious contrasts are often found to be very happily felt in\nsuch pictures, but without spirit, owing to a dread of the motley.\n\n\n## THE MOTLEY.\n\n\n\n896.\n\nA picture may easily become party-coloured or motley, when the colours\nare placed next each other in their full force, as it were only\nmechanically and according to uncertain impressions.\n\n897.\n\nIf, on the other hand, weak colours are combined, even although they\nmay be dissonant, the effect, as a matter of course, is not striking.\nThe uncertainty of the artist is communicated to the spectator, who, on\nhis side, can neither praise nor censure.\n\n898.\n\nIt is also important to observe that the colours may be disposed\nrightly in themselves, but that a work may still appear motley, if they\nare falsely arranged in relation to light and shade.\n\n899.\n\nThis may the more easily occur as light and shade are already defined\nin the drawing, and are, as it were, comprehended in it, while the\ncolour still remains open to selection.\n\n\n## DREAD OF THEORY.\n\n\n\n900.\n\nA dread of, nay, a decided aversion for all theoretical views\nrespecting colour and everything belonging to it, has been hitherto\nfound to exist among painters; a prejudice for which, after all, they\nwere not to be blamed; for what has been hitherto called theory was\ngroundless, vacillating, and akin to empiricism. We hope that our\nlabours may tend to diminish this prejudice, and stimulate the artist\npractically to prove and embody the principles that have been explained.\n\n\n## ULTIMATE AIM.\n\n\n\n901.\n\nBut without a comprehensive view of the whole of our theory, the\nultimate object will not be attained. Let the artist penetrate himself\nwith all that we have stated. It is only by means of harmonious\nrelations in light and shade, in keeping, in true and characteristic\ncolouring, that a picture can be considered complete, in the sense we\nhave now learnt to attach to the term.\n\n\n## GROUNDS.\n\n\n\n902.\n\nIt was the practice of the earlier artists to paint on light grounds.\nThis ground consisted of gypsum, and was thickly spread on linen or\npanel, and then levigated. After the outline was drawn, the subject was\nwashed in with a blackish or brownish colour. Pictures prepared in\nthis manner for colouring are still in existence, by Leonardo da Vinci,\nand Fra Bartolomeo; there are also several by Guido.--Note I I.\n\n903.\n\nWhen the artist proceeded to colour, and had to represent white\ndraperies, he sometimes suffered the ground to remain untouched.\nTitian did this latterly when he had attained the greatest certainty\nin practice, and could accomplish much with little labour. The whitish\nground was left as a middle tint, the shadows painted in, and the high\nlights touched on.--Note K K.\n\n904.\n\nIn the process of colouring, the preparation merely washed as it were\nunderneath, was always effective. A drapery, for example, was painted\nwith a transparent colour, the white ground shone through it and gave\nthe colour life, so the parts previously prepared for shadows exhibited\nthe colour subdued, without being mixed or sullied.\n\n905.\n\nThis method had many advantages; for the painter had a light ground\nfor the light portions of his work and a dark ground for the shadowed\nportions. The whole picture was prepared; the artist could work with\nthin colours in the shadows, and had always an internal light to give\nvalue to his tints. In our own time painting in water colours depends\non the same principles.\n\n906.\n\nIndeed a light ground is now generally employed in oil-painting,\nbecause middle tints are thus found to be more transparent, and are in\nsome degree enlivened by a bright ground; the shadows, again, do not so\neasily become black.\n\n907.\n\nIt was the practice for a time to paint on dark grounds. Tintoret\nprobably introduced them. Titian's best pictures are not painted on a\ndark ground.\n\n908.\n\nThe ground in question was red-brown, and when the subject was drawn\nupon it, the strongest shadows were laid in; the colours of the lights\nimpasted very thickly in the bright parts, and scumbled towards the\nshadows, so that the dark ground appeared through the thin colour as a\nmiddle tint. Effect was attained in finishing by frequently going over\nthe bright parts and touching on the high lights.\n\n909.\n\nIf this method especially recommended itself in practice on account\nof the rapidity it allowed of, yet it had pernicious consequences.\nThe strong ground increased and became darker, and the light colours\nlosing their brightness by degrees, gave the shadowed portions more\nand more preponderance. The middle tints became darker and darker, and\nthe shadows at last quite obscure. The strongly impasted lights alone\nremained bright, and we now see only light spots on the painting. The\npictures of the Bolognese school, and of Caravaggio, afford sufficient\nexamples of these results.\n\n910.\n\nWe may here in conclusion observe, that glazing derives its effect\nfrom treating the prepared colour underneath as a light ground. By\nthis operation colours may have the effect of being mixed to the eye,\nmay be enhanced, and may acquire what is called tone; but they thus\nnecessarily become darker.\n\n\n## PIGMENTS.\n\n\n\n911.\n\nWe receive these from the hands of the chemist and the investigator of\nnature. Much has been recorded respecting colouring substances, which\nis familiar to all by means of the press. But such directions require\nto be revised from time to time. The master meanwhile communicates his\nexperience in these matters to his scholar, and artists generally to\neach other.\n\n912.\n\nThose pigments which according to their nature are the most permanent,\nare naturally much sought after, but the mode of employing them also\ncontributes much to the duration of a picture. The fewest possible\ncolouring materials are to be employed, and the simplest methods of\nusing them cannot be sufficiently recommended.\n\n913.\n\nFor from the multitude of pigments colouring has suffered much. Every\npigment has its peculiar nature as regards its effect on the eye;\nbesides this it has its peculiar quality, requiring a corresponding\ntechnical method in its application. The former circumstance is a\nreason why harmony is more difficult of attainment with many materials\nthan with few, the latter, why chemical action and re-action may take\nplace among the colouring substances.\n\n914.\n\nWe may refer, besides, to some false tendencies which the artists\nsuffer themselves to be led away with. Painters are always looking\nfor new colouring substances, and believe when such a substance is\ndiscovered that they have made an advance in the art. They have a\ngreat curiosity to know the practical methods of the old masters, and\nlose much time in the search. Towards the end of the last century\nwe were thus long tormented with wax-painting. Others turn their\nattention to the discovery of new methods, through which nothing new is\naccomplished; for, after all, it is the feeling of the artist only that\ninforms every kind of technical process.\n\n\n## ALLEGORICAL, SYMBOLICAL, MYSTICAL APPLICATION OF COLOUR.\n\n\n\n915.\n\nIt has been circumstantially shown above, that every colour produces\na distinct impression on the mind, and thus addresses at once the eye\nand feelings. Hence it follows that colour may be employed for certain\nmoral and æsthetic ends.\n\n916.\n\nSuch an application, coinciding entirely with nature, might be called\nsymbolical, since the colour would be employed in conformity with its\neffect, and would at once express its meaning. If, for example, pure\nred were assumed to designate majesty, there can be no doubt that this\nwould be admitted to be a just and expressive symbol. All this has been\nalready sufficiently entered into.\n\n917.\n\nAnother application is nearly allied to this; it might be called the\nallegorical application. In this there is more of accident and caprice,\ninasmuch as the meaning of the sign must be first communicated to us\nbefore we know what it is to signify; what idea, for instance, is\nattached to the green colour, which has been appropriated to hope?\n\n918.\n\nThat, lastly, colour may have a mystical allusion, may be readily\nsurmised, for since every diagram in which the variety of colours may\nbe represented points to those primordial relations which belong both\nto nature and the organ of vision, there can be no doubt that these may\nbe made use of as a language, in cases where it is proposed to express\nsimilar primordial relations which do not present themselves to the\nsenses in so powerful and varied a manner. The mathematician extols\nthe value and applicability of the triangle; the triangle is revered\nby the mystic; much admits of being expressed in it by diagrams, and,\namong other things, the law of the phenomena of colours; in this case,\nindeed, we presently arrive at the ancient mysterious hexagon.\n\n919.\n\nWhen the distinction of yellow and blue is duly comprehended, and\nespecially the augmentation into red, by means of which the opposite\nqualities tend towards each other and become united in a third; then,\ncertainly, an especially mysterious interpretation will suggest itself,\nsince a spiritual meaning may be connected with these facts; and when\nwe find the two separate principles producing green on the one hand and\nred in their intenser state, we can hardly refrain from thinking in the\nfirst case on the earthly, in the last on the heavenly, generation of\nthe Elohim.--Note L L.\n\n920.\n\nBut we shall do better not to expose ourselves, in conclusion, to\nthe suspicion of enthusiasm; since, if our doctrine of colours finds\nfavour, applications and allusions, allegorical, symbolical, and\nmystical, will not fail to be made, in conformity with the spirit of\nthe age.\n\n\n## CONCLUDING OBSERVATIONS.\n\n\n\nIn reviewing this labour, which has occupied me long, and which at\nlast I give but as a sketch, I am reminded of a wish once expressed\nby a careful writer, who observed that he would gladly see his works\nprinted at once as he conceived them, in order then to go to the task\nwith a fresh eye; since everything defective presents itself to us more\nobviously in print than even in the cleanest manuscript. This feeling\nmay be imagined to be stronger in my case, since I had not even an\nopportunity of going through a fair transcript of my work before its\npublication, these pages having been put together at a time when a\nquiet, collected state of mind was out of the question.[5]\n\nSome of the explanations I was desirous of giving are to be found in\nthe introduction, but in the portion of my work to be devoted to the\nhistory of the doctrine of colours, I hope to give a more detailed\naccount of my investigations and the vicissitudes they underwent. One\ninquiry, however, may not be out of place here; the consideration,\nnamely, of the question, what can a man accomplish who cannot devote\nhis whole life to scientific pursuits? what can he perform as a\ntemporary guest on an estate not his own, for the advantage of the\nproprietor?\n\nWhen we consider art in its higher character, we might wish that\nmasters only had to do with it, that scholars should be trained by\nthe severest study, that amateurs might feel themselves happy in\nreverentially approaching its precincts. For a work of art should be\nthe effusion of genius, the artist should evoke its substance and form\nfrom his inmost being, treat his materials with sovereign command, and\nmake use of external influences only to accomplish his powers.\n\nBut if the professor in this case has many reasons for respecting\nthe dilettante, the man of science has every motive to be still more\nindulgent, since the amateur here is capable of contributing what may\nbe satisfactory and useful. The sciences depend much more on experiment\nthan art, and for mere experiment many a votary is qualified.\nScientific results are arrived at by many means, and cannot dispense\nwith many hands, many heads. Science may be communicated, the treasure\nmay be inherited, and what is acquired by one may be appropriated\nby many. Hence no one perhaps ought to be reluctant to offer his\ncontributions. How much do we not owe to accident, to mere practice,\nto momentary observation. All who are endowed only with habits of\nattention, women, children, are capable of communicating striking and\ntrue remarks.\n\nIn science it cannot therefore be required, that he who endeavours\nto furnish something in its aid should devote his whole life to it,\nshould survey and investigate it in all its extent; for this, in most\ncases, would be a severe condition even for the initiated. But if we\nlook through the history of science in general, especially the history\nof physics, we shall find that many important acquisitions have been\nmade by single inquirers, in single departments, and very often by\nunprofessional observers.\n\nTo whatever direction a man may be determined by inclination or\naccident, whatever class of phenomena especially strike him, excite\nhis interest, fix his attention, and occupy him, the result will still\nbe for the advantage of science: for every new relation that comes to\nlight, every new mode of investigation, even the imperfect attempt,\neven error itself is available; it may stimulate other observers and is\nnever without its use as influencing future inquiry.\n\nWith this feeling the author himself may look back without regret\non his endeavours. From this consideration he can derive some\nencouragement for the prosecution of the remainder of his task; and\nalthough not satisfied with the result of his efforts, yet re-assured\nby the sincerity of his intentions, he ventures to recommend his past\nand future labours to the interest of his contemporaries and posterity.\n\nMulti pertransibunt et augebitur scientia.\n\n\n[1] Plate 1, fig. 3.\n\n[2] See Note C.\n\n[3] Some early Italian writers, Sicillo, Occolti, Rinaldi, and others,\nhave treated this subject in connexion with the supposed signification\nof colours.--T.\n\n[4] The English technical expressions \"flat\" and \"square\" have an\nassociation of mannerism.--T\n\n[5] Towards the close of 1806, when Weimar was occupied by Napoleon\nafter the battle of Jena.--T.\n\n\n\n\n## NOTES.\n\n\n\nNOTE A.--Par. 18.\n\nLeonardo da Vinci observes that \"a light object relieved on a dark\nground appears magnified;\" and again, \"Objects seen at a distance\nappear out of proportion; this is because the light parts transmit\ntheir rays to the eye more powerfully than the dark. A woman's white\nhead-dress once appeared to me much wider than her shoulders, owing\nto their being dressed in black.\"[1] \"It is now generally admitted\nthat the excitation produced by light is propagated on the retina a\nlittle beyond the outline of the image. Professor Plateau, of Ghent,\nhas devoted a very interesting special memoir to the description\nand explanation of phenomena of this nature. See his 'Mémoire sur\nl'Irradiation,' published in the 11th vol. of the Transactions of the\nRoyal Academy of Sciences at Brussels.\"[2]--S. F.\n\n\nNOTE B.--Par. 23.\n\n\"The duration of ocular spectra produced by strongly exciting the\nretina, may be conveniently measured by minutes and seconds; but to\nascertain the duration of more evanescent phenomena, recourse must be\nhad to other means. The Chevalier d'Arcy (Mém. de l'Acad. des Sc.\n1765,) endeavoured to ascertain the duration of the impression produced\nby a glowing coal in the following manner. He attached it to the\ncircumference of a wheel, the velocity of which was gradually increased\nuntil the apparent trace of the object formed a complete circle, and\nthen measured the duration of a revolution, which was obviously that\nof the impression. To ascertain the duration of a revolution it is\nsufficient merely to know the number of revolutions described in a\ngiven time. Recently more refined experiments of the same kind have\nbeen made by Professors Plateau and Wheatstone.\"--S. F.\n\n\n[1] \"Trattato della Pittura, Roma, 1817,\" p. 143-223. This edition,\npublished from a Vatican MS., contains many observations not included\nin former editions.\n\n[2] A few notes (marked with inverted commas and with the signature S.\nF.) have been kindly furnished by a scientific friend.\n\n\nNOTE C.--Par. 50.\n\nEvery treatise on the harmonious combination of colours contains the\ndiagram of the chromatic circle more or less elaborately constructed.\nThese diagrams, if intended to exhibit the contrasts produced by\nthe action and re-action of the retina, have one common defect. The\nopposite colours are made equal in intensity; whereas the complemental\ncolour pictured on the retina is always less vivid, and always darker\nor lighter than the original colour. This variety undoubtedly accords\nmore with harmonious effects in painting.\n\nThe opposition of two pure hues of equal intensity, differing only in\nthe abstract quality of colour, would immediately be pronounced crude\nand inharmonious. It would not, however, be strictly correct to say\nthat such a contrast is too violent; on the contrary, it appears the\ncontrast is not carried far enough, for though differing in colour,\nthe two hues may be exactly similar in purity and intensity. Complete\ncontrast, on the other hand, supposes dissimilarity in all respects.\n\nIn addition to the mere difference of hue, the eye, it seems, requires\ndifference in the lightness or darkness of the hue. The spectrum of a\ncolour relieved as a dark on a light ground, is a light colour on a\ndark ground, and _vice versâ_. Thus, if we look at a bright red wafer\non the whitest surface, the complemental image will be still lighter\nthan the white surface; if the same wafer is placed on a black surface,\nthe complemental image will be still darker. The colour of both these\nspectra may be called greenish, but it is evident that a colour must be\nscarcely appreciable as such, if it is lighter than white and darker\nthan black. It is, however, to be remarked, that the white surface\nround the light greenish image seems tinged with a reddish hue, and\nthe black surface round the dark image becomes slightly illuminated\nwith the same colour, thus in both cases assisting to render the image\napparent (58).\n\nThe difficulty or impossibility of describing degrees of colour in\nwords, has also had a tendency to mislead, by conveying the idea of\nmore positive hues than the physiological contrast warrants. Thus,\nsupposing scarlet to be relieved as a dark, the complemental colour is\nso light in degree and so faint in colour, that it should be called a\npearly grey; whereas the theorists, looking at the quality of colour\nabstractedly, would call it a green-blue, and the diagram would falsely\npresent such a hue equal in intensity to scarlet, or as nearly equal as\npossible.\n\nEven the difference of mass which good taste requires may be suggested\nby the physiological phenomena, for unless the complemental image is\nsuffered to fall on a surface precisely as near to the eye as that on\nwhich the original colour was displayed, it appears larger or smaller\nthan the original object (22), and this in a rapidly increasing\nproportion. Lastly, the shape itself soon becomes changed (26).\n\nThat vivid colour demands the comparative absence of colour, either\non a lighter or darker scale, as its contrast, may be inferred again\nfrom the fact that bright colourless objects produce strongly coloured\nspectra. In darkness, the spectrum which is first white, or nearly\nwhite, is followed by red: in light, the spectrum which is first black,\nis followed by green (39-44). All colour, as the author observes\n(259), is to be considered as half-light, inasmuch as it is in every\ncase lighter than black and darker than white. Hence no contrast of\ncolour with colour, or even of colour with black or white, can be so\ngreat (as regards lightness or darkness) as the contrast of black and\nwhite, or light and dark abstractedly. This distinction between the\ndifferences of degree and the differences of kind is important, since a\njust application of contrast in colour may be counteracted by an undue\ndifference in lightness or darkness. The mere contrast of colour is\nhappily employed in some of Guido's lighter pictures, but if intense\ndarks had been opposed to his delicate carnations, their comparative\nwhiteness would have been unpleasantly apparent. On the other hand, the\nflesh-colour in Giorgione, Sebastian del Piombo (his best imitator),\nand Titian, was sometimes so extremely glowing[1] that the deepest\ncolours, and black, were indispensable accompaniments. The manner of\nTitian as distinguished from his imitation of Giorgione, is golden\nrather than fiery, and his biographers are quite correct in saying\nthat he was fond of opposing red (lake) and blue to his flesh[2]. The\ncorrespondence of these contrasts with the physiological phenomena will\nbe immediately apparent, while the occasional practice of Rubens in\nopposing bright red to a still cooler flesh-colour, will be seen to be\nequally consistent.\n\nThe effect of white drapery (the comparative absence of colour) in\nenhancing the glow of Titian's flesh-colour, has been frequently\npointed out:[3] the shadows of white thus opposed to flesh, often\npresent, again, the physiological contrast, however delicately,\naccording to the hue of the carnation. The lights, on the other hand,\nare not, and probably never were, quite white, but from the first,\npartook of the quality of depth, a quality assumed by the colourists to\npervade every part of a picture more or less.[4]\n\nIt was before observed that the description of colours in words may\noften convey ideas of too positive a nature, and it may be remarked\ngenerally that the colours employed by the great masters are, in their\nultimate effect, more or less subdued or broken. The physiological\ncontrasts are, however, still applicable in the most comparatively\nneutral scale.\n\nAgain, the works of the colourists show that these oppositions are\nnot confined to large masses (except perhaps in works to be seen only\nat a great distance); on the contrary, they are more or less apparent\nin every part, and when at last the direct and intentional operations\nof the artist may have been insufficient to produce them in their\nminuter degrees, the accidental results of glazing and other methods\nmay be said to extend the contrasts to infinity. In such productions,\nwhere every smallest portion is an epitome of the whole, the eye\nstill appreciates the fascinating effect of contrast, and the work is\npronounced to be true and complete, in the best sense of the words.\n\nThe Venetian method of scumbling and glazing exhibits these minuter\ncontrasts within each other, and is thus generally considered more\nrefined than the system of breaking the colours, since it ensures a\nfuller gradation of hues, and produces another class of contrasts,\nthose, namely, which result from degrees of transparence and opacity.\nIn some of the Flemish and Dutch masters, and sometimes in Reynolds,\nthe two methods are combined in great perfection.\n\nThe chromatic diagram does not appear to be older than the last\ncentury. It is one of those happy adaptations of exacter principles to\nthe objects of taste which might have been expected from Leonardo da\nVinci. That its true principle was duly felt is abundantly evident from\nthe works of the colourists, as well as from the general observations\nof early writers.[5] The more practical directions occasionally to be\nmet with in the treatises of Leon Battista Alberti, Leonardo da Vinci\nand others, are conformable to the same system. Some Italian works,\nnot written by painters, which pretend to describe this harmony, are,\nhowever, very imperfect.[6] A passage in Lodovico Dolce's Dialogue on\nColours is perhaps the only one worth quoting. \"He,\" says that writer,\n\"who wishes to combine colours that are agreeable to the eye, will\nput grey next dusky orange; yellow-green next rose-colour; blue next\norange; dark purple, black, next dark-green; white next black, and\nwhite next flesh-colour.\"[7] The Dialogue on Painting, by the same\nauthor, has the reputation of containing some of Titian's precepts:\nif the above passage may be traced to the same source, it must be\nconfessed that it is almost the only one of the kind in the treatise\nfrom which it is taken.\n\n\n[1] \"Ardito veramente alquanto, sanguigno, e quasi\nfiammeggiante.\"--_Zanetti della Pittura Veneziana_, Ven. 1771, p.\n90. Warm as the flesh colour of the colourists is, it still never\napproaches a positive hue, if we except some examples in frescoes and\nother works intended to be seen at a great distance. Zanetti, speaking\nof a fresco by Giorgione, now almost obliterated, compares the colour\nto \"un vivo raggio di cocente sole.\"---_Varie Pitture a fresco dei\nPrincipali Maestri Veneziani_. Ven. 1760.\n\n[2] Ridolfi.\n\n[3] Zanetti, I. ii.\n\n[4] Two great authorities, divided by more than three centuries, Leon\nBattista Alberti and Reynolds, have recommended this subdued treatment\nof white. \"It is to be remembered,\" says the first, \"that no surface\nshould be made so white that it cannot be made more so. In white\ndresses again, it is necessary to stop far short of the last degree of\nwhiteness.\"--_Della Pittura_, I. ii., compare with Reynolds, vol. i.\ndis. 8.\n\n[5] Vasari observes, \"L'unione nella pittura è una discordanza\ndicolori diversi accordati insième.\"--Vol. i. c. 18. This observation\nis repeated by various writers on art in nearly the same words, and\nat last appears in Sandrart: \"Concordia, potissimum picturæ decus,\nin discordiâ consistit, et quasi litigio colorum.\"--P. i. c. 5. The\nsource, perhaps, is Aristotle: he observes, \"We are delighted with\nharmony, because it is the union of contrary principles having a ratio\nto each other.\"--_Problem._\n\n[6] See \"Occolti Trattato de' Colori.\" Parma, 1568.\n\n[7] \"Volendo l'uomo accoppiare insième colori che all'occhio\ndilettino--porrà insième il berrettino col leonato; il verde-giallo con\nl'incarnato e rosso; il turchino con l'arangi; il morello col verde\noscuro; il nero col bianco; il bianco con l'incarnato.\"--_Dialogo di\nM. Lodovico Dolce nel quale si ragiona della qualità, diversità, e\nproprietà de' colori_. Venezia, 1565.\n\n\n\nNOTE D.--Par. 66.\n\nIn some of these cases there can be no doubt that Goethe attributes\nthe contrast too exclusively to the physiological cause, without\nmaking sufficient allowance for the actual difference in the colour of\nthe lights. The purely physical nature of some coloured shadows was\npointed out by Pohlmann; and Dr. Eckermann took some pains to convince\nGoethe of the necessity of making such a distinction. Goethe at first\nadhered to his extreme view, but some time afterwards confessed to\nDr. Eckermann, that in the case of the blue shadows of snow (74), the\nreflection of the sky was undoubtedly to be taken into the account.\n\"Both causes may, however, operate together,\" he observed, \"and the\ncontrast which a warm yellow light demands may heighten the effect of\nthe blue.\" This was all his opponent contended.[1]\n\nWith a few such exceptions, the general theory of Goethe with regard\nto coloured shadows is undoubtedly correct; the experiments with two\ncandles (68), and with coloured glass and fluids (80), as well as the\nobservations on the shadows of snow (75), are conclusive, for in all\nthese cases only one light is actually changed in colour, while the\nother still assumes the complemental hue. \"Coloured shadows,\" Dr. J.\nMüller observes, \"are usually ascribed to the physiological influence\nof contrast; the complementary colour presented by the shadow being\nregarded as the effect of internal causes acting on that part of the\nretina, and not of the impression of coloured rays from without. This\nexplanation is the one adopted by Rumford, Goethe, Grotthuss, Brandes,\nTourtual, Pohlmann, and most authors who have studied the subject.\"[2]\n\nIn the Historical Part the author gives an account of a scarce French\nwork, \"Observations sur les Ombres Colorées,\" Paris, 1782. The\nwriter[3] concludes that \"the colour of shadows is as much owing to\nthe light that causes them as to that which (more faintly) illumines\nthem.\"\n\n\n[1] Eckermann's \"Gespräche mit Goethe,\" vol. ii. p. 76 and 280.\n\n[2] \"Elements of Physiology,\" by J. Müller, M. D., translated from the\nGerman by William Baly, M.D. London, 1839.\n\n[3] Anonymous, having only given the initials H. F. T.\n\n\n\nNOTE E.--Par. 69.\n\nThis opinion of the author is frequently repeated (201, 312, 591), and\nas it seems at first sight to be at variance with a received principle\nof art, it may be as well at once to examine it.\n\nIn order to see the general proposition in its true point of view,\nit will be necessary to forget the arbitrary distinctions of light\nand shade, and to consider all such modifications between highest\nbrightness and absolute darkness only as so many lesser degrees of\nlight.[1] The author, indeed, by the word shadow, always understands a\nlesser light.\n\nThe received notion, as stated by Du Fresnoy,[2] is much too positive\nand unconditional, and is only true when we understand the \"displaying\"\nlight to comprehend certain degrees of half or reflected light, and the\n\"destroying\" shade to mean the intensest degree of obscurity.\n\nThere are degrees of brightness which destroy colour as well as\ndegrees of darkness.[3] In general, colour resides in a mitigated\nlight, but a very little observation shows us that different colours\nrequire different degrees of light to display them. Leonardo da Vinci\nfrequently inculcates the general principle above alluded to, but he\nas frequently qualifies it; for he not only remarks that the highest\nlight may be comparative privation of colour, but observes, with great\ntruth, that some hues are best displayed in their fully illumined\nparts, some in their reflections, and some in their half-lights; and\nagain, that every colour is most beautiful when lit by reflections from\nits own surface, or from a hue similar to its own.[4]\n\nThe Venetians went further than Leonardo in this view and practice;\nand he seems to allude to them when he criticises certain painters,\nwho, in aiming at clearness and fulness of colour, neglected what, in\nhis eyes, was of superior importance, namely, gradation and force of\nchiaro-scuro.[5]\n\nThat increase of colour supposes increase of darkness, as so often\nstated by Goethe, may be granted without difficulty. To what extent, on\nthe other hand, increase of darkness, or rather diminution of light,\nis accompanied by increase of colour, is a question which has been\nvariously answered by various schools. Examples of the total negation\nof the principle are not wanting, nor are they confined to the infancy\nof the art. Instances, again, of the opposite tendency are frequent\nin Venetian and early Flemish pictures resembling the augmenting\nrichness of gems or of stained glass:[6] indeed, it is not impossible\nthat the increase of colour in shade, which is so remarkable in the\npictures alluded to, may have been originally suggested by the rich\nand fascinating effect of stained glass; and the Venetians, in this as\nin many other respects, may have improved on a hint borrowed from the\nearly German painters, many of whom painted on glass.[7]\n\nAt all events, the principle of still increasing in colour in certain\nhues seems to have been adopted in Flanders and in Venice at an early\nperiod;[8] while Giorgione, in carrying the style to the most daring\nextent, still recommended it by corresponding grandeur of treatment in\nother respects.\n\nThe same general tendency, except that the technical methods are\nless transparent, is, however, very striking in some of the painters\nof the school of Umbria, the instructors or early companions of\nRaphael.[9] The influence of these examples, as well as that of Fra\nBartolommeo, in Florence, is distinctly to be traced in the works of\nthe great artist just named, but neither is so marked as the effect\nof his emulation of a Venetian painter at a later period. The glowing\ncolour, sometimes bordering on exaggeration, which Raphael adopted\nin Rome, is undoubtedly to be attributed to the rivalry of Sebastian\ndel Piombo. This painter, the best of Giorgione's imitators, arrived\nin Rome, invited by Agostini Chigi, in 1511, and the most powerful of\nRaphael's frescoes, the Heliodorus and Mass of Bolsena, as well as\nsome portraits in the same style, were painted in the two following\nyears. In the hands of some of Raphael's scholars, again, this extreme\nwarmth was occasionally carried to excess, particularly by Pierino del\nVaga, with whom it often degenerated into redness. The representative\nof the glowing manner in Florence was Fra Bartolommeo, and, in the\nsame quality, considered abstractedly, some painters of the school of\nFerrara were second to none.\n\nIn another Note (par. 177) some further considerations are offered,\nwhich may partly explain the prevalence of this style in the beginning\nof the sixteenth century; here we merely add, that the conditions under\nwhich the appearance itself is most apparent in nature are perhaps more\nobvious in Venice than elsewhere. The colour of general nature may be\nobserved in all places with almost equal convenience, but with regard\nto an important quality in living nature, namely, the colour of flesh,\nperhaps there are no circumstances in which its effects at different\ndistances can be so conveniently compared as when the observer and the\nobserved gradually approach and glide past each other on so smooth an\nelement and in so undisturbed a manner as on the canals and in the\ngondolas of Venice;[10] the complexions, from the peculiar mellow\ncarnations of the Italian women to the sun-burnt features and limbs\nof the mariners, presenting at the same time the fullest variety in\nanother sense.\n\nAt a certain distance--the colour being always assumed to be unimpaired\nby interposed atmosphere--the reflections appear kindled to intenser\nwarmth; the fiery glow of Giorgione is strikingly apparent; the colour\nis seen in its largest relation; the _macchia_,[11] an expression so\nemphatically used by Italian writers, appears in all its quantity, and\nthe reflections being the focus of warmth, the hue seems to deepen in\nshade.\n\nA nearer view gives the detail of cooler tints more perceptibly,[12]\nand the forms are at the same time more distinct. Hence Lanzi is quite\ncorrect when, in distinguishing the style of Titian from that of\nGiorgione, he says that Titian's was at once more defined and less\nfiery.[13] In a still nearer observation the eye detects the minute\nlights which Leonardo da Vinci says are incompatible with effects such\nas those we have described[14] and which, accordingly, we never find\nin Giorgione and Titian. This large impression of colour, which seems\nto require the condition of comparative distance for its full effect,\nwas most fitly employed by the same great artists in works painted in\nthe open air or for large altar-pieces. Their celebrated frescoes on\nthe exterior of the Fondaco de' Tedeschi at Venice, to judge from their\nfaint remains and the descriptions of earlier writers, were remarkable\nfor extreme warmth in the shadows. The old frescoes in the open air\nthroughout Friuli have often the same character, and, owing to the\nfulness of effect which this treatment ensures, are conspicuous at a\nvery great distance.[15]\n\nIn assuming that the Venetian painters may have acquired a taste for\nthis breadth[16] of colour under the circumstances above alluded to,\nit is moreover to be remembered that the time for this agreeable\nstudy was the evening; when the sun had already set behind the hills\nof Bassano; when the light was glowing but diffused; when shadows\nwere soft--conditions all agreeing with the character of their\ncolouring:[17] above all, when the hour invited the fairer portion of\nthe population to betake themselves in their gondolas to the lagunes.\nThe scene of this \"promenade\" was to the north of Venice, the quarter\nin which Titian at one time lived. A letter exists written by Francesco\nPriscianese, giving an account of his supping with the great painter in\ncompany with Jacopo Nardi, Pietro Aretino, the sculptor Sansovino, and\nothers. The writer speaks of the beauty of the garden, where the table\nwas prepared, looking over the lagunes towards Murano, \"which part of\nthe sea,\" he continues, \"as soon as the sun was down, was covered with\na thousand gondolas, graced with beautiful women, and enlivened by the\nharmony of voices and instruments, which lasted till midnight, forming\na pleasing accompaniment to our cheerful repast.\"[18]\n\nTo return to Goethe: perhaps the foregoing remarks may warrant the\nconclusion that his idea of colour in shadow is not irreconcileable\nwith the occasional practice of the best painters. The highest examples\nof the style thus defined are, or were, to be found in the works of\nGiorgione[19] and Titian, and hence the style itself, though \"within\nthat circle\" few \"dare walk\" is to be considered the grandest and\nmost perfect. Its possible defects or abuse are not to be dissembled:\nin addition to the danger of exaggeration[20] it is seldom united\nwith the plenitude of light and shade, or with roundness; yet, where\nfine examples of both modes of treatment may be compared, the charm\nof colour has perhaps the advantage.[21] The difficulty of uniting\nqualities so different in their nature, is proved by the very rare\ninstances in which it has been accomplished. Tintoret in endeavouring\nto add chiaro-scuro to Venetian colour, in almost every instance fell\nshort of the glowing richness of Titian.[22]\n\nGiacomo Bassan and his imitators, even in their dark effects, still had\nthe principle of the gem in view: their light, in certain hues, is the\nminimum of colour, their lower tones are rich, their darks intense,\nand all is sparkling.[23] Of the great painters who, beginning, on\nthe other hand, with chiaro-scuro, sought to combine with it the full\nrichness of colour, Correggio, in the opinion of many, approached\nperfection nearest; but we may perhaps conclude with greater justice\nthat the desired excellence was more completely attained by Rembrandt\nthan by any of the Italians.\n\n\n[1] Leonardo da Vinci observes: \"L'ombra è diminuzione di luce, tenebre\nè privazione di luce.\" And again: \"Sempre il minor lume è ombra del\nlume maggiore.\"--_Trattato della Pittura_, pp. 274-299.\n\nN. B. The same edition before described has been consulted throughout.\n\n[2]\n\n    \"Lux varium vivumque dabit, nullum umbra colorem.\"\n                                             _De Arte Graphicá_.\n\n    \"Know first that light displays and shade destroys\n    Refulgent nature's variegated dies.\"--Mason's _Translation_.\n\n\n[3] A Spanish writer, Diego de Carvalho e Sampayo, quoted by Goethe\n(\"Farbenlehre,\" vol. ii.), has a similar observation. This destroying\neffect of light is striking in climates where the sun is powerful, and\nwas not likely to escape the notice of a Spaniard.\n\n[4] Trattato, pp. 103, 121, 123, 324, &c.\n\n[5] Ib. pp. 85, 134.\n\n[6] Absolute opacity, to judge from the older specimens of stained\nglass, seems to have been considered inadmissible. The window was\nto admit light, however modified and varied, in the form prescribed\nby the architect, and that form was to be preserved. This has been\nunfortunately lost sight of in some modern glass-painting, which,\nby excluding the light in large masses, and adopting the opacity\nof pictures (the reverse of the influence above alluded to), has\ninterfered with the architectural symmetry in a manner far from\ndesirable. On the other hand, if we suppose painting at any period\nto have aimed at the imitation of stained glass, such an imitation\nmust of necessity have led to extreme force; for the painter sets\nout by substituting a mere white ground for the real light of the\nsky, and would thus be compelled to subdue every tone accordingly.\nIn such an imitation his colour would soon deepen to its intensest\nstate; indeed, considerable portions of the darker hues would be lost\nin obscurity. The early Flemish pictures seldom err on the side of\na gay superabundance of colour; on the contrary, they are generally\nremarkable for comparatively cool lights, for extreme depth, and a\ncertain subdued splendour, qualities which would necessarily result\nfrom the imitation or influence in question.\n\n[7] See Langlois, \"Peinture sur Verre.\" Rouen, 1832; Descamps, \"La Vie\ndes Peintres Flamands;\" and Gessert, \"Geschichte der Glasmalerei.\"\nStutgard, 1839. The antiquity of the glass manufactory of Murano\n(Venice) is also not to be forgotten. Vasari objects to the Venetian\nglass, because it was darker in colour than that of Flanders, France,\nand England; but this very quality was more likely to have an\nadvantageous influence on the style of the early oil-painters. The use\nof stained glass was, however, at no period very general in Italy.\n\n[8] Zanetti, \"Della Pittura Veneziana,\" marks the progress of the early\nVenetian painters by the gradual use of the warm outline. There are\nsome mosaics in St. Mark's which have the effect of flesh-colour, but\non examination, the only red colour used is found to be in the outlines\nand markings. Many of the drawings of the old masters, heightened with\nred in the shadows, have the same effect. In these drawings the artists\njudiciously avoided colouring the lips and cheeks much, for this would\nonly have betrayed the want of general colour, as is observable when\nstatues are so treated.\n\n[9] Andrea di Luigi, called L'Ingegno, and Niccolo di Fuligno, are\ncited as the most prominent examples. See Rumohr, \"Italienische\nForschungen.\" Perogino himself occasionally adopted a very glowing\ncolour.\n\nThe early Italian schools which adhered most to the Byzantine types\nappear to have been also the most remarkable for depth, or rather\ndarkness, of colour. This fidelity to customary representation was\nsometimes, as in the schools of Umbria, and to a certain extent in\nthose of Siena and Bologna, the result of a religious veneration for\nthe ancient examples; in others, as in Venice, the circumstance of\nfrequent intercourse with the Levant is also to be taken into the\naccount. The Greek pictures of the Madonna, not to mention other\nrepresentations, were extremely dark, in exaggerated conformity,\nit is supposed, with the tradition respecting her real complexion\n(see D'Agincourt, vol. iv. p. 1); a belief which obtained so late as\nLomazzo's time, for, speaking of the Madonna, he observes, \"Leggesi\nperò che fu alquanto bruna.\" Giotto, who with the independence of\ngenius betrayed a certain contempt for these traditions, failed perhaps\nto unite improvement with novelty when he substituted a pale white\nflesh-colour for the traditional brown. Some specimens of his works,\nstill existing at Padua, present a remarkable contrast in this respect\nwith the earliest productions of the Venetian and Paduan artists. His\nworks at Florence differ as widely from those of the earlier painters\nof Tuscany. This peculiarity was inherited by his imitators, and at\none time almost characterised the Florentine school. Leon Battista\nAlberti was not perhaps the first who objected to it (\"Vorrei io\nche dai pittori fosse comperato il color bianco assai più caro che\nle presiosissime gemme.\"--_Della Pittura_, I. ii.) The attachment\nof Fra Bartolommeo to the grave character of the Christian types is\nexemplified in his deep colouring, as well as in other respects.\n\n[10] Holland might be excepted, and in Holland similar causes may have\nhad a similar influence.\n\n[11] Local colour; literally, the _blot_.\n\n[12] Zanetti ventures to single out the picture of Tobit and the Angel\nin S. Marziale as the first example of Titian's own manner, and in\nwhich a direct imitation of Giorgione is no longer apparent. In this\npicture the lights are cool and the blood-tint very effective.\n\n[13] \"Meno sfumato, men focoso.\"--_Storia Pittorica_.\n\n[14] \"La prima cosa che de' colori si perde nelle distante è il lustro,\nloro minima parte.\"--_Trattato_, p. 213; and elsewhere, \"I lumi\nprincipali in picciol luogo son quelli che in picciola distanza sono i\nprimi che si perdono all' occhio.\"--p. 128.\n\n[15] A colossal St. Christopher, the usual subject, is frequently seen\noccupying the whole height of the external wall of a church. We have\nhere an example of the influence of religion, such as it was, even on\nthe style of colouring and practical methods of the art. The mere sight\nof the image of St. Christopher, the type of strength, was considered\nsufficient to reinvigorate those who were exhausted by the labours of\nhusbandry. The following is a specimen of the inscriptions inculcating\nthis belief:--\n\n    \"Christophori Sancti speciem quicumque tuetur,\n    Illo namque die nullo languore tenetur.\"\n\nHence the practice of painting the figure on the outside of churches,\nhence its colossal size, and hence the powerful qualities in colour\nabove described. See Maniago, \"Storia delle Belle Arti Friulane.\"\n\n[16] The authority of Fuseli sufficiently warrants the application of\nthe term breadth to colour; he speaks of Titian's \"breadth of local\ntint.\"\n\n[17] Zanetti quotes an opinion of the painters of his time to the same\neffect:--\"Teneano essi (alcuni maestri) per cosa certa, che in molte\nopere Tiziano volesse fingere il lume--quale si vede nell' inclinarsi\ndel sole verso la sera. Gli orizzonti assai luminosi dietro le\nmontagne, le ombre incerte e più le carnagioni brunette e rosseggianti\ndelle figure, gl'induceano a creder questo.\"--Lib. ii. Leonardo da\nVinci observes, \"Quel corpo che si troverà in mediocre lume fia in\nlui poca differenza da' lumi all' ombre. E questo accade sul far\ndella sera--e queste opere sono dolci ed hacci grazia ogni qualità di\nvolto,\" &c.--p. 336. Elsewhere, \"Le ombre fatte dal sole od altri lumi\nparticolari sono senza grazia.\"--p. 357; see also p. 247.\n\n[18] See \"Francesco Priscianese De' Primi Principii della Lingua\nLatina,\" Venice, 1550. The letter is at the end of the work. It is\nquoted in Ticozzi's \"Vite de' Pittori Vecelli,\" Milan, 1817.\n\n[19] The works of Giorgione are extremely rare. The pictures best\ncalculated to give an idea of the glowing manner for which he\nis celebrated, are the somewhat early works and several of the\naltar-pieces of Titian, the best specimens of Palma Vecchio, and the\nportraits of Sebastian del Piombo.\n\n[20] Zanetti and Lodovico Dolce mention Lorenzo Lotto as an instance\nof the excess of Giorgione's style. Titian himself sometimes\noverstepped the mark, as his biographers confess, and as appears,\namong other instances, from the head of St. Peter in the picture (now\nin the Vatican) in which the celebrated St. Sebastian is introduced.\nRaphael was criticised by some cardinals for a similar defect. See\n\"Castiglione, Il Cortigiano,\" 1. ii.\n\nIn the same paragraph to which the present observations refer, the\nauthority of Kircher is quoted; his treatise, \"Ars magna lucis et\numbrae,\" was published in Rome in 1646. In a portrait of Nicholas\nPoussin, engraved by Clouet, the painter is represented holding a book,\nwhich, from the title and the circumstance of Poussin having lived in\nRome in Kircher's time, Goethe supposes to be the work in question. The\nabuse of the principle above alluded to, is perhaps exemplified in the\nred half-tints observable in some of Poussin's figures.\n\nThe augmentation of colour in subdued light was still more directly\ntaught by Lomazzo. He composes the half-tints of flesh merely by\ndiminishing the quantity of white, the proportions of the other colours\nemployed (for he enters into minute details) remaining unaltered. See\nhis \"Trattato della arte della Pittura,\" Milan, 1584, p. 301.\n\n[21] In the Dresden Gallery, a picture attributed to Titian--at\nall events a lucid Venetian picture--hangs next the St. George of\nCorreggio. After looking at the latter, the Venetian work appears\nglassy and unsubstantial, but on reversing the order of comparison,\nthe Correggio may be said to suffer more, and for a moment its fine\ntransitions of light and shade seem changed to heaviness.\n\n[22] The finest works of Tintoret---the Crucifixion and the Miracolo\ndel Servo (considered here merely with reference to their colour,)\nmay be said to combine the excellences of Titian and Giacomo Bassan,\non a grand scale; the sparkling clearness of the latter is one of the\nprominent characteristics of these pictures. Tintoret is reported to\nhave once said that a union of his own knowledge of form with Bassan's\ncolour would be the perfection of painting. See \"Verei Notizie de'\nPittori di Bassano;\" Ven. 1775, p. 61.\n\n[23] That this last quality, the characteristic of Bassan's best\npictures, was held in high estimation by Paul Veronese, is not only\nevident from that painter's own works, but from the circumstance of his\npreferring to place his sons with Bassan rather than with any other\npainter. (See \"Boschini Carta del Navegar,\" p. 280.) The Baptism of\nSta. Lucilla, in Boschini's time considered the finest of Giacomo's\nworks, is still in the church of S. Valentino, at Bassano, and may be\nconsidered the type of the lucid and sparkling manner.\n\n\n\nNOTE F.--Par. 83.\n\nThe author, in these instances, seems to be anticipating his\nsubsequent explanations on the effect of semi-transparent mediums.\nFor an explanation of the general view contained in these paragraphs\nrespecting the gradual increase of colour from high light, see the last\nNote.\n\nThe anonymous French work before alluded to, among other interesting\nexamples, contains a chapter on shadows cast by the upper light of the\nsky and coloured by the setting sun. The effect of this remarkable\ncombination is, that the light on a wall is most coloured immediately\nunder a projecting roof, and becomes comparatively neutralised in\nproportion to its distance from the edge of the darkest shade.\n\n\nNOTE G.--Par. 98.\n\n\"The simplest case of the phenomenon, which Goethe calls a subjective\nhalo, and one which at once explains its cause, is the following.\nRegard a red wafer on a sheet of white paper, keeping the eye\nstedfastly fixed on a point at its center. When the retina is\nfatigued, withdraw the head a little from the paper, and a green halo\nwill appear to surround the wafer. By this slight increase of distance\nthe image of the wafer itself on the retina becomes smaller, and the\nocular spectrum which before coincided with the direct image, being\nnow relatively larger, is seen as a surrounding ring.\"--S. F. Goethe\nmentions cases of this kind, but does not class them with subjective\nhalos. See Par. 30.\n\n\nNOTE H.--Par. 113.\n\n\"Cases of this kind are by no means uncommon. Several interesting\nones are related in Sir John Herschell's article on Light in the\nEncyclopædia Metropolitana. Careful investigation has, however, shown\nthat this defect of vision arises in most, if not in all cases, from\nan inability to perceive the red, not the blue rays. The terms are so\nconfounded by the individuals thus affected, that the comparison of\ncolours in their presence is the only criterion.\"--S. F.\n\n\nNOTE I.--Par. 135.\n\nThe author more than once admits that this chapter on \"Pathological\nColours\" is very incomplete, and expresses a wish (Par. 734) that some\nmedical physiologists would investigate the subject further. This was\nafterwards in a great degree accomplished by Dr. Johannes Müller, in\nhis memoir \"Über die Phantastischen Gesichtserscheinungen.\" Coblentz,\n1826. Similar phenomena have been also investigated with great labour\nand success by Purkinje. For a collection of extraordinary facts of the\nkind recorded by these writers, the reader may consult Scott's Letters\non Demonology and Witchcraft.[1] The instances adduced by Müller and\nothers are, however, intended to prove the inherent capacity of the\norgan of vision to produce light and colours. In some maladies of the\neye, the patient, it seems, suffers the constant presence of light\nwithout external light. The exciting principle in this case is thus\nproved to be within, and the conclusion of the physiologists is that\nexternal light is only one of the causes which produce luminous and\ncoloured impressions. That this view was anticipated by Newton may be\ngathered from the concluding \"query\" in the third book of his Optics.\n\n\n[1] See also a curious passage on the beatific vision of the monks of\nMount Athos, in Gibbon, chap. 63.\n\n\n\nNOTE K.--Par. 140.\n\n\"Catoptrical colours. The colours included under this head are\nprincipally those of fibres and grooved surfaces; they can be produced\nartificially by cutting parallel grooves on a surface of metal from\n2000 to 10,000 in the inch. See 'Brewster's Optics,' p. 120. The\ncolours called by Goethe _paroptical_, correspond with those produced\nby the diffraction or inflection of light in the received theory.--See\nBrewster, p. 95. The phenomena included under the title 'Epoptical\nColours,' are generally known as the colours of thin plates. They vary\nwith the thickness of the film, and the colour seen by reflection\nalways differs from that seen by transmission. The laws of these\nphenomena have been thoroughly investigated. See Nobili, and Brewster,\np. 100.\"--S. F.\n\nThe colours produced by the transmission of polarised light through\nchrystalised mediums, were described by Goethe, in his mode,\nsubsequently to the publication of his general theory, under the name\nof Entoptic Colours. See note to Par. 485.\n\n\nNOTE L.--Par. 150.\n\nWe have in this and the next paragraph the outline of Goethe's system.\nThe examples that follow seem to establish the doctrine here laid\ndown, but there are many cases which it appears cannot be explained on\nsuch principles: hence, philosophers generally prefer the theory of\nabsorption, according to which it appears that certain mediums \"have\nthe property of absorbing some of the component rays of white light,\nwhile they allow the passage of others.\"[1]\n\nWhether all the facts adduced by Goethe--for instance, that recorded\nin Par. 172, are to be explained by this doctrine, we leave to the\ninvestigators of nature to determine. Dr. Eckermann, in conversing with\nGoethe, thus described the two leading phenomena (156, 158) as seen by\nhim in the Alps. \"At a distance of eighteen or twenty miles at mid-day\nin bright sunshine, the snow appeared yellow or even reddish, while the\ndark parts of the mountain, free from snow, were of the most decided\nblue. The appearances did not surprise me, for I could have predicted\nthat the mass of the interposed medium would give a deep yellow tone\nto the white snow, but I was pleased to witness the effect, since it\nso entirely contradicted the erroneous views of some philosophers,\nwho assert that the air has a blue-tinging quality. The observation,\nsaid Goethe, is of importance, and contradicts the error you allude to\ncompletely.\"[2]\n\nThe same writer has some observations to the same effect on the colour\nof the Rhone at Geneva. A circumstance of an amusing nature which he\nrelates in confirmation of Goethe's theory, deserves to be inserted.\n\"Here (at Strasburg), passing by a shop, I saw a little glass bust\nof Napoleon, which, relieved as it was against the dark interior of\nthe room, exhibited every gradation of blue, from milky light blue\nto deep violet. I foresaw that the bust seen from within the shop\nwith the light behind it, would present every degree of yellow, and I\ncould not resist walking in and addressing the owner, though perfectly\nunknown to me. My first glance was directed to the bust, in which, to\nmy great joy, I saw at once the most brilliant colours of the warmer\nkind, from the palest yellow to dark ruby red. I eagerly asked if I\nmight be allowed to purchase the bust; the owner replied that he had\nonly lately brought it with him from Paris, from a similar attachment\nto the emperor to that which I appeared to feel, but, as my ardour\nseemed far to surpass his, I deserved to possess it. So invaluable\ndid this treasure seem in my eyes, that I could not help looking at\nthe good man with wonder as he put the bust into my hands for a few\nfranks. I sent it, together with a curious medal which I had bought\nin Milan, as a present to Goethe, and when at Frankfort received the\nfollowing letter from him.\" The letter, which Dr. Eckermann gives\nentire, thus concludes--\"When you return to Weimar you shall see the\nbust in bright sunshine, and while the transparent countenance exhibits\na quiet blue,[3] the thick mass of the breast and epaulettes glows with\nevery gradation of warmth, from the most powerful ruby-red downwards;\nand as the granite statue of Memnon uttered harmonious sounds, so the\ndim glass image displays itself in the pomp of colours. The hero is\nvictorious still in supporting the Farbenlehre.\"[4]\n\nOne effect of Goethe's theory has been to invite the attention of\nscientific men to facts and appearances which had before been unnoticed\nor unexplained. To the above cases may be added the very common, but\nvery important, fact in painting, that a light warm colour, passed in\na semi-transparent state over a dark one, produces a cold, bluish\nhue, while the operation reversed, produces extreme warmth. On the\njudicious application of both these effects, but especially of the\nlatter, the richness and brilliancy of the best-coloured pictures\ngreatly depends. The principle is to be recognised in the productions\nof schools apparently opposite in their methods. Thus the practice\nof leaving the ground, through which a light colour is apparent, as\na means of ensuring warmth and depth, is very common among the Dutch\nand Flemish painters. The Italians, again, who preferred a solid\nunder-painting, speak of internal light as the most fascinating quality\nin colour. When the ground is entirely covered by solid painting, as\nin the works of some colourists, the warmest tints in shadows and\nreflections have been found necessary to represent it. This was the\npractice of Rembrandt frequently, and of Reynolds universally, but the\nglow of their general colour is still owing to its being repeatedly\nor ultimately enriched on the above principle. Lastly, the works of\nthose masters who were accustomed to paint on dark grounds are often\nheavy and opaque; and even where this influence of the ground was\novercome, the effects of time must be constantly diminishing the warmth\nof their colouring as the surface becomes rubbed and the dark ground\nmore apparent through it. The practice of painting on dark grounds was\nintended by the Carracci to compel the students of their school to\naim at the direct imitation of the model, and to acquire the use of\nthe brush; for the dark ground could only be overcome by very solid\npainting. The result answered their expectations as far as dexterity of\npencil was concerned, but the method was fatal to brilliancy of colour.\nAn intelligent writer of the seventeenth century[5] relates that Guido\nadopted his extremely light style from seeing the rapid change in some\nworks of the Carracci soon after they were done. It is important,\nhowever, to remark, that Guido's remedy was external rather than\ninternal brilliancy; and it is evident that so powerless a brightness\nas white paint can only acquire the splendour of light by great\ncontrast, and, above all, by being seen through external darkness. The\nsecret of Van Eyck and his contemporaries is always assumed to consist\nin the vehicle (varnish or oils) he employed; but a far more important\ncondition of the splendour of colour in the works of those masters was\nthe careful preservation of internal light by painting thinly, but\nultimately with great force, on white grounds. In some of the early\nFlemish pictures in the Royal Gallery at Munich, it may be observed,\nthat wherever an alteration was made by the painter, so that a light\ncolour is painted over a dark one, the colour is as opaque as in any\nof the more modern pictures which are generally contrasted with such\nworks. No quality in the vehicle could prevent this opacity under such\ncircumstances; and on the other hand, provided the internal splendour\nis by any means preserved, the vehicle is comparatively unimportant.\n\nIt matters not (say the authorities on these points) whether the effect\nin question is attained by painting thinly over the ground, in the\nmanner of the early Flemish painters and sometimes of Rubens, or by\npainting a solid light preparation to be afterwards toned to richness\nin the manner of the Venetians. Among the mechanical causes of the\nclearness of colours superposed on a light preparation may be mentioned\nthat of careful grinding. All writers on art who have descended to\npractical details have insisted on this. From the appearance of some\nVenetian pictures it may be conjectured that the colours of the\nsolid under-painting were sometimes less perfectly ground than the\nscumbling colours (the light having to pass through the one and to\nbe reflected from the other). The Flemish painters appear to have\nused carefully-ground pigments universally. This is very evident in\nFlemish copies from Raphael, which, though equally impasted with\nthe originals, are to be detected, among other indications, by the\nfinely-ground colours employed.\n\n\n[1] See \"Müller's Elements of Physiology,\" translated from the German\nby William Baly, M.D. \"The laws of absorption,\" it has been observed,\n\"have not been studied with so much success as those of other phenomena\nof physical optics, but some excellent observations on the subject\nwill be found in Herschell's Treatise on Light in the Encyclopædia\nMetropolitana, § III.\"\n\n[2] \"Eckermann's Gespräche mit Goethe,\" vol. ii. p. 280. Leonardo da\nVinci had made precisely the same observation. \"A distant mountain will\nappear of a more beautiful blue in proportion as it is dark in colour.\nThe illumined air, interposed between the eye and the dark mass, being\nthinner towards the summit of the mountain, will exhibit the darkness\nas a deeper blue and _vice versâ_.\"--_Trattato della Pittura_, p. 143.\nElsewhere--\"The air which intervenes between the eye and dark mountains\nbecomes blue; but it does not become blue in (before) the light part,\nand much less in (before) the portion that is covered with snow.\"--p.\n244.\n\n[3] This supposes either that the mass was considerably thicker, or\nthat there was a dark ground behind the head, and a light ground behind\nthe rest of the figure.\n\n[4] \"Eckermann's Gespräche mit Goethe,\" vol. ii. p. 242.\n\n[5] Scanelli, \"Microcosmo della Pittura,\" Cesena, 1657, p. 114.\n\n\n\nNOTE M.--Par. 177.\n\nWithout entering further into the scientific merits or demerits of\nthis chapter on the \"First Class of Dioptrical Colours,\" it is to be\nobserved that several of the examples correspond with the observations\nof Leonardo da Vinci, and again with those of a much older authority,\nnamely, Aristotle. Goethe himself admits, and it has been remarked by\nothers, that his theory, in many respects, closely resembles that of\nAristotle: indeed he confesses[1] that at one time he had an intention\nof merely paraphrasing that philosopher's Treatise on Colours.[2]\n\nWe have already remarked (Note on par. 150) that Goethe's notion with\nregard to the production of warm colours, by the interposition of dark\ntransparent mediums before a light ground, agrees with the practice of\nthe best schools in colouring; and it is not impossible that the same\nreasons which may make this part of the doctrine generally acceptable\nto artists now, may have recommended the very similar theory of\nAristotle to the painters of the fifteenth and sixteenth centuries:\nat all events, it appears that the ancient theory was known to those\npainters.\n\nIt is unnecessary to dwell on the fact that the doctrines of Aristotle\nwere enthusiastically embraced and generally inculcated at the period\nin question;[3] but it has not been observed that the Italian writers\nwho translated, paraphrased, and commented on Aristotle's Treatise\non Colours in particular, were in several instances the personal\nfriends of distinguished painters. Celio Calcagnini[4] had the highest\nadmiration for Raphael; Lodovico Dolce[5] was the eulogist of Titian;\nPortius,[6] whose amicable relations with the Florentine painters may\nbe inferred from various circumstances, lectured at Florence on the\nAristotelian doctrines early in the sixteenth century. The Italian\ntranslations were later, but still prove that these studies were\nundertaken with reference to the arts, for one of them is dedicated to\nthe painter Cigoli.[7]\n\nThe writers on art, from Leon Battista Alberti to Borghini, without\nmentioning later authorities, either tacitly coincide with the\nAristotelian doctrine, or openly profess to explain it. It is true this\nis not always done in the clearest manner, and some of these writers\nmight say with Lodovico Dolce, \"I speak of colours, not as a painter,\nfor that would be the province of the divine Titian.\"\n\nLeonardo da Vinci in his writings, as in everything else, appears as\nan original genius. He now and then alludes generally to opinions\nof \"philosophers,\" but he quotes no authority ancient or modern.\nNevertheless, a passage on the nature of colours, particularly where\nhe speaks of the colours of the elements, appears to be copied from\nLeon Battista Alberti,[8] and from the mode in which some of Leonardo's\npropositions are stated, it has been supposed[9] that he had been\naccustomed at Florence to the form of the Aristotelian philosophy. At\nall events, some of the most important of his observations respecting\nlight and colours, have a great analogy with those contained in the\ntreatise in question. The following examples will be sufficient to\nprove this coincidence; the corresponding passages in Goethe are\nindicated, as usual, by the numbers of the paragraphs; the references\nto Leonardo's treatise are given at the bottom of the page.\n\n    Aristotle.\n\n    \"A vivid and brilliant red appears when the weak rays of the\n    sun are tempered by subdued and shadowy white,\"--154.\n\n    Leonardo\n\n    \"The air which is between the sun and the earth at sun-rise\n    or sun-set, always invests what is beyond it more than any\n    other (higher) portion of the air: this is because it is\n    whiter.\"[10]\n\n    A bright object loses its whiteness in proportion to its\n    distance from the eye much more when it is illuminated by\n    the sun, for it partakes of the colour of the sun mingled\n    with the colour (tempered by the mass) of the air interposed\n    between the eye and the brightness.[11]\n\n    Aristotle.\n\n    \"If light is overspread with much obscurity, a red colour\n    appears; if the light is brilliant and vivid, this red\n    changes to a flame-colour.\"[12]--150, 160.\n\n    Leonardo.\n\n    \"This (the effect of transparent colours on various grounds)\n    is evident in smoke, which is blue when seen against black,\n    but when it is opposed to the (light) blue sky, it appears\n    brownish and reddening.\"[13]\n\n    Aristotle.\n\n    \"White surfaces as a ground for colours, have the effect of\n    making the pigments[14] appear in greater splendour.\"--594,\n    902.\n\n    Leonardo.\n\n    \"To exhibit colours in their beauty, the whitest ground\n    should be prepared. I speak of colours that are (more or\n    less) transparent.\"[15]\n\n    Aristotle.\n\n    \"The air near us appears colourless; but when seen in depth,\n    owing to its thinness it appears blue;[16] for where the\n    light is deficient (beyond it), the air is affected by the\n    darkness and appears blue: in a very accumulated state,\n    however, it appears, as is the case with water, quite\n    white.\"--155, 158.\n\n    Leonardo.\n\n    \"The blue of the atmosphere is owing to the mass of\n    illuminated air interposed between the darkness above and\n    the earth. The air in itself has no colour, but assumes\n    qualities according to the nature of the objects which are\n    beyond it. The blue of the atmosphere will be the more\n    intense in proportion to the degree of darkness beyond it:\"\n    elsewhere--\"if the air had not darkness beyond it, it would\n    be white.\"[17]\n\n    Aristotle.\n\n    \"We see no colour in its pure state, but every hue is\n    variously intermingled with others: even when it is\n    uninfluenced by other colours, the effect of light and\n    shade modifies it in various ways, so that it undergoes\n    alterations and appears unlike itself. Thus, bodies seen in\n    shade or in light, in more pronounced or softer sun-shine,\n    with their surfaces inclined this way or that, with every\n    change exhibit a different colour.\"\n\n    Leonardo.\n\n    \"No substance will ever exhibit its own hue unless the light\n    which illumines it is entirely similar in colour. It very\n    rarely happens that the shadows of opaque bodies are really\n    similar (in colour) to the illumined parts. The surface of\n    every substance partakes of as many hues as are reflected\n    from surrounding objects.\"[18]\n\n    Aristotle.\n\n    \"So, again, with regard to the light of fire, of the moon,\n    or of lamps, each has a different colour, which is variously\n    combined with differently coloured objects.\"\n\n    Leonardo.\n\n    \"We can scarcely ever say that the surface of illumined\n    bodies exhibits the real colour of those bodies. Take a\n    white band and place it in the dark, and let it receive\n    light by means of three apertures from the sun, from fire,\n    and from the sky: the white band will be tricoloured.\"[19]\n\n    Aristotle.\n\n    \"When the light falls on any object and assumes (for\n    example) a red or green tint, it is again reflected on other\n    substances, thus undergoing a new change. But this effect,\n    though it really takes place, is not appreciable by the\n    eye: though the light thus reflected to the eye is composed\n    of a variety of colours, the principal of these only are\n    distinguishable.\"\n\n    Leonardo.\n\n    \"No colour reflected on the surface of another colour,\n    tinges that surface with its own colour (merely), but will\n    be mixed with various other reflections impinging on the\n    same surface:\" but such effects, he observes elsewhere, \"are\n    scarcely, if at all, distinguishable in a very diffused\n    light.\"[20]\n\n    Aristotle.\n\n    \"Thus, all combinations of colours are owing to three\n    causes: the light, the medium through which the light\n    appears, such as water or air, and lastly the local colour\n    from which the light happens to be reflected.\"\n\n    Leonardo.\n\n    \"All illumined objects partake of the colour of the light\n    they receive.\n\n    \"Every opaque surface partakes of the colour of the\n    intervening transparent medium, according to the density of\n    such medium and the distance between the eye and the object.\n\n    \"The medium is of two kinds; either it has a surface, like\n    water, &c., or it is without a common surface, like the\n    air.\"[21]\n\nIn the observations on trees and plants more points of resemblance\nmight be quoted; the passages corresponding with Goethe's views are\nmuch more numerous.\n\nIt is remarkable that Leonardo, in opposition, it seems to some\nauthorities,[22] agrees with Aristotle in reckoning black and white\nas colours, placing them at the beginning and end of the scale.[23]\nLike Aristotle, again, he frequently makes use of the term black, for\nobscurity; he even goes further, for he seems to consider that blue\nmay be produced by the actual mixture of black and white, provided they\nare pure.[24] The ancient author, however, explains himself on this\npoint as follows--\"We must not attempt to make our observations on\nthese effects by mixing colours as painters mix them, but by remarking\nthe appearances as produced by the rays of light mingling with each\nother.\"[25]\n\nWhen we consider that Leonardo's Treatise professes to embrace the\nsubject of imitation in painting, and that Aristotle's briefly examines\nthe physical nature and appearance of colours, it must be admitted\nthat the latter sustains the above comparison with advantage; and it\nis somewhat extraordinary that observations indicating so refined a\nknowledge of nature, as regards the picturesque, should not have been\ntaken into the account, for such appears to be the fact, in the various\nopinions and conjectures that have been expressed from time to time on\nthe painting of the Greeks. The treatise in question must have been\nwritten when Apelles painted, or immediately before; and as a proof\nthat Aristotle's remarks on the effect of semi-transparent mediums were\nnot lost on the artists of his time, the following passage from Pliny\nis subjoined, for, though it is well known, it acquires additional\ninterest from the foregoing extracts.\n\n\"He (Apelles) passed a dark colour over his pictures when finished, so\nthin that it increased the splendour of the tints, while it protected\nthe surface from dust and dirt: it could only be seen on looking into\nthe picture. The effect of this operation, judiciously managed, was to\nprevent the colours from being too glaring, and to give the spectator\nthe impression of looking through a transparent crystal. At the same\ntime it seemed almost imperceptibly to add a certain dignity of tone to\ncolours that were too florid.\" \"This,\" says Reynolds, \"is a true and\nartist-like description of glazing or scumbling, such as was practised\nby Titian and the rest of the Venetian painters.\"\n\nThe account of Pliny has, in this instance, internal evidence\nof truth, but it is fully confirmed by the following passage in\nAristotle:--\"Another mode in which the effect of colours is exhibited\nis when they appear through each other, as painters employ them when\nthey glaze (ἐπαλειφοντες)[26] a (dark) colour over a lighter one; just\nas the sun, which is in itself white, assumes a red colour when seen\nthrough darkness and smoke. This operation also ensures a variety of\ncolours, for there will be a certain ratio between those which are on\nthe surface and those which are in depth.\"--_De Sensu et Sensili_.\n\nAristotle's notion respecting the derivation of colours from white and\nblack may perhaps be illustrated by the following opinion on the very\nsimilar theory of Goethe.\n\n\"Goethe and Seebeck regard colour as resulting from the mixture of\nwhite and black, and ascribe to the different colours a quality\nof darkness (σκιερὸν), by the different degrees of which they are\ndistinguished, passing from white to black through the gradations\nof yellow, orange, red, violet, and blue, while green appears to be\nintermediate again between yellow and blue. This remark, though it has\nno influence in weakening the theory of colours proposed by Newton,\nis certainly correct, having been confirmed experimentally by the\nresearches of Herschell, who ascertained the relative intensity of the\ndifferent coloured rays by illuminating objects under the microscope by\ntheir means, &c.\n\n\"Another certain proof of the difference in brightness of the different\ncoloured rays is afforded by the phenomena of ocular spectra. If, after\ngazing at the sun, the eyes are closed so as to exclude the light, the\nimage of the sun appears at first as a luminous or white spectrum upon\na dark ground, but it gradually passes through the series of colours to\nblack, that is to say, until it can no longer be distinguished from the\ndark field of vision; and the colours which it assumes are successively\nthose intermediate between white and black in the order of their\nilluminating power or brightness, namely, yellow, orange, red, violet,\nand blue. If, on the other hand, after looking for some time at the\nsun we turn our eyes towards a white surface, the image of the sun is\nseen at first as a black spectrum upon the white surface, and gradually\npasses through the different colours from the darkest to the lightest,\nand at last becomes white, so that it can no longer be distinguished\nfrom the white surface\"[27]--See par 40, 44.\n\nIt is not impossible that Aristotle's enumeration of the colours may\nhave been derived from, or confirmed by, this very experiment. Speaking\nof the after-image of colours he says, \"The impression not only exists\nin the sensorium in the act of perceiving, but remains when the organ\nis at rest. Thus if we look long and intently on any object, when\nwe change the direction of the eyes a responding colour follows. If\nwe look at the sun, or any other very bright object, and afterwards\nshut our eyes, we shall, as if in ordinary vision, first see a colour\nof the same kind; this will presently be changed to a red colour,\nthen to purple, and so on till it ends in black and disappears.\"--_De\nInsomniis_.\n\n\n[1] \"Geschichte der Farbenlehre,\" in the \"Nachgelassene Werke.\" Cotta,\n1833.\n\n[2] The treatise in question is ascribed by Goethe to Theophrastus,\nbut it is included in most editions of Aristotle, and even attributed\nto him in those which contain the works of both philosophers; for\ninstance, in the Aldine Princeps edition, 1496. Calcagnini says, the\ntreatise is made up of two separate works on the subject, both by\nAristotle.\n\n[3] His authority seems to have been equally great on subjects\nconnected with the phenomena of vision; the Italian translator of\na Latin treatise, by Portius, on the structure and colours of the\neye, thus opens his dedication to the Cardinal Ercole Gonzaga, of\nMantua:--\"Grande anzi quasi infinito è l'obligo che ha il mondo con\nquel più divino che umano spirito di Aristotile.\"\n\n[4] In a letter to Ziegler the mathematician, Calcagnini speaks of\nRaphael as \"the first of painters in the theory as well as in the\npractice of his art.\" This expression may, however, have had reference\nto a remarkable circumstance mentioned in the same letter, namely,\nthat Raphael entertained the learned Fabius of Ravenna as a constant\nguest, and employed him to translate Vitruvius into Italian. This MS.\ntranslation, with marginal notes, written by Raphael, is now in the\nlibrary at Munich. \"Passavant, Rafael von Urbino.\"\n\n[5] Lodovico Dolce's Treatise on Colours (1565) is in the form of a\ndialogue, like his \"Aretino.\" The abridged theory of Aristotle is\nfollowed by a translation of the Treatise of Antonius Thylesius on\nColours; this is adapted to the same colloquial form, and the author is\nnot acknowledged: the book ends with an absurd catalogue of emblems.\nThe \"Somma della Filosofia d'Aristotile,\" published earlier by the same\nauthor, is a very careless performance.\n\n[6] A Latin translation of Aristotle's Treatise on Colours, with\ncomments by Simon Portius, was first published, according to Goethe,\nat Naples in 1537. In a later Florentine edition, 1548, dedicated to\nCosmo I., Portius alludes to his having lectured at an earlier period\nin Florence on the doctrines of Aristotle, at which time he translated\nthe treatise in question. Another Latin translation, with notes, was\npublished later in the same century at Padua--\"Emanuele Marguino\nInterprete:\" but by far the clearest view of the Aristotelian theory\nis to be found in the treatise of Antonio Vidi Scarmiglione of Fuligno\n(\"De Coloribus,\" Marpurgi, 1591). It is dedicated to the Emperor\nRudolph II. Of all the paraphrases of the ancient doctrine this comes\nnearest to the system of Goethe; but neither this nor any other of the\nworks alluded to throughout this Note are mentioned by the author in\nhis History of the Doctrine of Colours, except that of Portius.\n\n[7] An earlier Italian translation appeared in Rome, 1535. See\n\"Argelatus Biblioteca degli Volgarizzatori.\"\n\n[8] \"Della Pittura e della Statua,\" Lib. I, p. 16, Milan edition,\n1804. Compare with the \"Trattato della Pittura,\" p. 141. Other points\nof resemblance are to be met with. The notion of certain colours\nappropriated to the four elements, occurs in Aristotle, and is indeed\nattributed to older writers.\n\n[9] See the notes to the Roman edition of the \"Trattato della Pittura.\"\n\n[10] Page 237.\n\n[11] Page 301.\n\n[12] In the Treatise _De Igne_, by Theophrastus, we find the same\nnotion thus expressed: \"Brightness (_τὸ λευκὸν_) seen through a\ndark coloured medium (_διὰ του μέλανος_) appears red; as the sun\nseen through smoke or soot: hence the coal is redder than the\nflame.\" Scarmiglione, from whom Kircher seems to have copied,\nobserves:--\"Itaque color realis est lux opaca; licet id e plurimis\napparentiis colligere. Luna enim in magnâ solis eclipsi rubra\nconspicitur, quia tenebris lux præpeditur ac veluti tegitur.\"--_De\nColoribus_.\n\n[13] Page 122.\n\n[14] _Τὰ ἂνθη_: translated _flores_ by Calcagnini and the rest, by\nGoethe, _die Blüthe_, the bloom. That the word sometimes signified\npigments is sufficiently apparent from the following passage of\nSuidas (quoted by Emeric David, \"Discours Historiques sur la Peinture\nModerne\") _ἂνθεσι κεκοσμημέναι, οἶον ψιμμιωίῳ φύκει καὶ τοῖς ὸμοίοις_.\nVariis pigmentis ornatæ, ut cerussâ, fuco, et aliis similibus. (Suid.\nin voc. _Ἐξμηθισμένας_.) A panel prepared for painting, with a white\nground consolidated with wax, and perhaps mastic, was found in\nHerculaneum.\n\n[15] Page 114.\n\n[16] _Ἐν βάθει δὲ θεωρουμίνου ιγγυτάτω φαίνεται τῶ χρώματι κυανονοειδὴς\nδιὰ τὴν ὰραιότητα._ \"But when seen in depth, it appears (even) in its\nnearest colour, blue, owing to its thinness.\" The Latin interpretations\nvary very much throughout. The point which is chiefly important is\nhowever plain enough, viz. that darkness seen through a light medium is\nblue.\n\n[17] Page 136-430.\n\n[18] Page 121, 306, 326, 387.\n\n[19] Page 306.\n\n[20] Page 104, 369.\n\n[21] Page 236, 260, 328.\n\n[22] \"De' semplici colori il primo è il bianco: beuchè i filosofi non\naccettano nè il bianco nè il nero nel numero de' colori.\"--p. 125, 141.\nElsewhere, however, he sometimes adopts the received opinion.\n\n[23] Leon Battista Alberti, in like manner observes:--\"Affermano (i\nfilosofi) che le spezie de' colori sono sette, cioè, che il bianco ed\nil nero sono i duoi estremi, infra i quali ve n'è uno nel mezzo (rosso)\ne che infra ciascuno di questi duoi estremi e quel del mezzo, da ogni\nparte ve ne sono due altri.\" An absurd statement of Lomazzo, p. 190,\nis copied verbatim from Lodovico Dolce (Somma della Filos. d'Arist.);\nbut elsewhere, p. 306, Lomazzo agrees with Alberti. Aristotle seems to\nhave misled the two first, for after saying there are seven colours,\nhe appears only to mention six: he says--\"There are seven colours, if\nbrown is to be considered equivalent to black, which seems reasonable.\nYellow, again, may be said to be a modification of white. Between these\nwe find red, purple, green, and blue.\"--_De Sensu et Sensili_. Perhaps\nit is in accordance with this passage that Leonardo da Vinci reckons\neight colours.--_Trattato_, p. 126.\n\n[24] Page 122, 142, 237.\n\n[25] On the authority of this explanation the word μιλάν has sometimes\nbeen translated in the foregoing extracts _obscurity, darkness_.\n\nRaffaello Borghini, in his attempt to describe the doctrine of\nAristotle with a view to painting, observes--\"There are two\nprinciples which concur in the production of colour, namely, light\nand transparence.\" But he soon loses this clue to the best part of\nthe ancient theory, and when he has to speak of the derivation of\ncolours from white and black, he evidently understands it in a mere\natomic sense, and adds--\"I shall not at present pursue the opinion\nof Aristotle, who assumes black and white as principal colours, and\nconsiders all the rest as intermediate between them.\"--_Il Riposo_, 1.\nii. Accordingly, like Lodovico Dolce, he proceeds to a subject where he\nwas more at home, namely, the symbolical meaning of colours.\n\n[26] This word is only strictly applied to unctuous substances, and may\nconfirm the views of those writers who have conjectured that asphaltum\nwas a chief ingredient in the _atramentum_ of the ancients.\n\n[27] \"Elements of Physiology,\" by J. Müller, M.D., translated from the\nGerman by William Baly, M.D. London, 1839.\n\n\n\nNOTE N.--Par. 246.\n\n\"The appearance of white in the centre, according to the Newtonian\ntheory, arises from each line of rays forming its own spectrum.\nThese spectra, superposing each other on all the middle part, leave\nuncorrected (unneutralised) colours only at the two edges.\"--S. F.[1]\n\n\n[1] This was objected to Goethe when his \"Beyträge sur Optik\" first\nappeared; he answered the objection by a coloured diagram in the plates\nto the \"Farbenlehre:\" in this he undertakes to show that the assumed\ngradual \"correction\" of the colours would produce results different\nfrom the actual appearance in nature.\n\n\n\nNOTE O.--Par. 252.\n\nThese experiments with grey objects, which exhibit different colours\nas they are on dark or light grounds, were suggested, Goethe tells\nus, by an observation of Antonius Lucas, of Lüttich, one of Newton's\nopponents, and, in the opinion of the author, one of the few who made\nany well-founded objections. Lucas remarks, that the sun acts merely\nas a circumscribed image in the prismatic experiments, and that if the\nsame sun had a lighter background than itself, the colours of the prism\nwould be reversed. Thus in Goethe's experiments, when the grey disk is\non a dark ground, it is edged with blue on being magnified; when on a\nlight ground it is edged with yellow. Goethe acknowledges that Lucas\nhad in some measure anticipated his own theory.--Vol. ii. p. 440.\n\n\n\nNOTE P.--Par. 284.\n\nThe earnestness and pertinacity with which Goethe insisted that\nthe different colours are not subject to different degrees of\nrefrangibility are at least calculated to prove that he was himself\nconvinced on the subject, and, however extraordinary it may seem, his\nconviction appears to have been the result of infinite experiments\nand the fullest ocular evidence. He returns to the question in the\ncontroversial division of his work, in the historical part, and again\nin the description of the plates. In the first he endeavours to show\nthat Newton's experiment with the blue and red paper depends entirely\non the colours being so contrived as to appear elongated or curtailed\nby the prismatic borders. \"If,\" he says, \"we take a light-blue instead\nof a dark one, the illusion (in the latter case) is at once evident.\nAccording to the Newtonian theory the yellow-red (red) is the least\nrefrangible colour, the violet the most refrangible. Why, then, does\nNewton place a blue paper instead of a violet next the red? If the\nfact were as he states it, the difference in the refrangibility of\nthe yellow-red and violet would be greater than in the case of the\nyellow-red and blue. But here comes in the circumstance that a violet\npaper conceals the prismatic borders less than a dark-blue paper, as\nevery observer may now easily convince himself,\" &c.--Polemischer\nTheil, par. 45. Desaguliers, in repeating the experiment, confessed\nthat if the ground of the colours was not black, the effect did\nnot take place so well. Goethe adds, \"not only not so well, but\nnot at all.\"--Historischer Theil, p. 459. Lucas of Lüttich, one of\nNewton's first opponents, denied that two differently-coloured silks\nare different in distinctness when seen in the microscope. Another\nexperiment proposed by him, to show the unsoundness of the doctrine of\nvarious refrangibility, was the following:--Let a tin plate painted\nwith the prismatic colours in stripes be placed in an empty cubical\nvessel, so that from the spectator's point of view the colours may be\njust hidden by the rim. On pouring water into this vessel, all the\ncolours become visible in the same degree; whereas, it was contended,\nif the Newtonian doctrine were true, some colours would be apparent\nbefore others.--Historischer Theil, p. 434.\n\nSuch are the arguments and experiments adduced by Goethe on this\nsubject; they have all probably been answered. In his analysis of\nNewton's celebrated _Experimentum Crucis_, he shows again that by\nreversing the prismatic colours (refracting a dark instead of a\nlight object), the colours that are the most refrangible in Newton's\nexperiment become the least so, and _vice versâ_.\n\nWithout reference to this objection, it is now admitted that \"the\ndifference of colour is not a test of difference of refrangibility, and\nthe conclusion deduced by Newton is no longer admissible as a general\ntruth, that to the same degree of refrangibility ever belongs the\nsame colour, and to the same colour ever belongs the same degree of\nrefrangibility.\"--Brewster's Optics, p. 72.\n\n\n\nNOTE Q--Par. 387.\n\nWith the exception of two very inconclusive letters to Sulpice\nBoisserée, and some incidental observations in the conclusion of the\nhistorical portion under the head of entoptic colours, Goethe never\nreturned to the rainbow. Among the plates he gave the diagram of\nAntonius de Dominis. An interesting chapter on halos, parhelia, and\nparaselenæ, will be found in Brewster's Optics, p. 270.\n\n\nNOTE R.--Par. 478.\n\nThe most complete exhibition of the colouring or mantling of metals\nwas attained by the late Cav. Nobili, professor of physical science in\nFlorence. The general mode in which these colours are produced is thus\nexplained by him:[1]--\n\n\"A point of platinum is placed vertically at the distance of about\nhalf a line above a lamina of the same metal laid horizontally at the\nbottom of a vessel of glass or porcelain. Into this vessel a solution\nof acetate of lead is poured so as to cover not only the lamina of\nplatinum, but two or three lines of the point as well. Lastly, the\npoint is put in communication with the negative pole of a battery, and\nthe lamina with the positive pole. At the moment in which the circuit\nis completed a series of coloured rings is produced on the lamina\nunder the point similar to those observed by Newton in lenses pressed\ntogether.\"\n\nThe scale of colours thus produced corresponds very nearly with that\nobserved by Newton and others in thin plates and films, but it is\nfuller, for it extends to forty-four tints. The following list, as\ngiven by Nobili, is divided by him into four series to agree with\nthose of Newton: the numbers in brackets are those of Newton's scale.\nThe Italian terms are untranslated, because the colours in some cases\npresent very delicate transitions.[2]\n\n    _First Series._\n\n    1. Biondo argentino (4).[3]    6. Fulvo acceso.\n    2. Biondo.                     7. Rosso di rame (6).\n    3. Biondo d'oro.               8. Ocria.\n    4. Biondo acceso (5).          9. Ocria violacea.\n    5. Fulvo.                     10. Rosso violaceo (7).\n\n    Second Series.\n\n    11. Violetto (8).              20. Giallo acceso.\n    12. Indaco (10).               21. Giallo-rancio.\n    13. Blu carico.                22. Rancio (13).\n    14. Blu.                       23. Rancio-rossiccio.\n    15. Blu chiaro (11)            24. Rancio-rosso.\n    16. Celeste.                   25. Rosso-rancio.\n    17. Celeste giallognolo.       26. Lacca-rancia (14).\n    18. Giallo chiarissimo (12).   27. Lacca.\n    19. Giallo.                    28. Lacca accesa (15).\n\n    Third Series.\n\n    29. Lacca-purpurea (16).       34. Verde-giallo (20).\n    30. Lacca-turchiniccia (17).   35. Verde-rancio.\n    31. Porpora-verdognola (18).   36. Rancio-verde (21).\n    32. Verde (19).                37. Rancio-roseo.\n    33. Verde giallognolo.         38. Lacca-rosea (22).\n\n\n    Fourth Series.\n\n    39. Lacca-violacea (24).        43. Verde-giallo rossiccio (28).\n    40. Violaceo-verdognolo (25).   44. Lacca-rosea (30).\n    41. Verde (26).\n    42. Verde-giallo (27).\n\n\"These tints,\" Professor Nobili observes, \"are disposed according to\nthe order of the thin mantlings which occasion them; the colour of\nthe thinnest film is numbered 1; then follow in order those produced\nby a gradual thickening of the medium. I cannot deceive myself in\nthis arrangement, for the thin films which produce the colours are\nall applied with the same electro-chemical process. The battery, the\nsolution, the distances, &c., are always the same; the only difference\nis the time the effect is suffered to last. This is a mere instant for\nthe colour of No. 1, a little longer for No. 2, and so on, increasing\nfor the succeeding numbers. Other criterions, however, are not wanting\nto ascertain the place to which each tint belongs.\"\n\nThe scale differs from that of Newton, inasmuch as there is no blue in\nNobili's first series and no green in the second: green only appears in\nthe third and fourth series. \"The first series,\" says the Professor,\n\"is remarkable for the fire and metallic appearance of its tints, the\nsecond for clearness and brilliancy, the third and fourth for force and\nrichness.\" The fourth, he observes, has the qualities of the third in a\nsomewhat lesser degree, but the two greens are very nearly alike.\n\nIt is to be observed, that red and green are the principal ingredients\nin the third and fourth series, blue and yellow in the second and first.\n\n\n[1] See \"Memorie ed Osservazioni, edite et inedite del Cav. Professor\nNobili,\" Firenze, 1834.\n\n[2] The colours in some of the compound terms are in a manner mutually\nneutralising; such terms might, no doubt, be amended.\n\n[3] The three first numbers in Newton's scale are black, blue, and\nwhite.\n\n\n\nNOTE S.--Par. 485.\n\nA chapter on entoptic colours, contained in the supplement to Goethe's\nworks, was translated with the intention of inserting it among the\nnotes, but on the whole it was thought most advisable to omit it. Like\nmany other parts of the \"Doctrine of Colours\" it might have served as\na specimen of what may be achieved by accurate observation unassisted\nby a mathematical foundation. The whole theory of the polarization of\nlight has, however, been so fully investigated since Goethe's time,\nthat the chapter in question would probably have been found to contain\nvery little to interest scientific readers, for whom it seems chiefly\nto have been intended. One observation occurs in it which indeed has\nmore reference to the arts; in order to make this intelligible, the\nleading experiment must be first described, and for this purpose the\nfollowing extracts may serve.\n\n3.[1]\n\n\"The experiment, in its simplest form, is to be made as follows:--let\na tolerably thick piece of plate-glass be cut into several squares of\nan inch and a half; let these be heated to a red heat and then suddenly\ncooled. The squares of glass which do not split in this operation are\nnow fit to produce the entoptic colours.\n\n4.\n\n\"In our mode of exhibiting the phenomenon, the observer is, above all,\nto betake himself, with his apparatus to the open air. All dark rooms,\nall small apertures (foramina exigua),[2] are again to be given up. A\npure, cloudless sky is the source whence we are derive a satisfactory\ninsight into the appearances.\n\n5.\n\n\"The atmosphere being clear, let the observer lay the squares above\ndescribed on a black surface, so placing them that two sides may\nbe parallel with the plane of vision. When the sun is low, let him\nhold the squares so as to reflect to the eye that portion of the sky\nopposite to the sun, and he will then perceive four dark points in\nthe four corners of a light space. If, after this, he turn towards\nthe quarters of the sky at right angles with that where his first\nobservation was made, he will see four bright points on a dark ground:\nbetween the two regions the figures appear to fluctuate.\n\n6.\n\n\"From this simple reflection we now proceed to another, which, but\nlittle more complicated, exhibits the appearance much more distinctly.\nA solid cube of glass, or in its stead a cube composed of several\nplates, is placed on a black mirror, or held a little inclined\nabove it, at sun-rise or sun-set. The reflection of the sky being\nnow suffered to fall through the cube on the mirror, the appearance\nabove described will appear more distinctly. The reflection of the\nsky opposite to the sun presents four dark points on a light ground;\nthe two lateral portions of the sky present the contrary appearance,\nnamely, four light points on a dark ground. The space not occupied by\nthe corner points appears in the first case as a white cross, in the\nother as a black cross, expressions hereafter employed in describing\nthe phenomena. Before sun-rise or after sun-set, in a very subdued\nlight, the white cross appears on the side of the sun also.[3]\n\n\"We thus conclude that the direct reflection of the sun produces a\nlight figure, which we call a white cross; the oblique reflection gives\na dark figure, which we call a black cross. If we make the experiment\nall round the sky, we shall find that a fluctuation takes place in the\nintermediate regions.\"\n\nWe pass over a variety of observations on the modes of exhibiting this\nphenomenon, the natural transparent substances which exhibit it best,\nand the detail of the colours seen within[4] them, and proceed to an\ninstance where the author was enabled to distinguish the \"direct\" from\nthe \"oblique\" reflection by means of the entoptic apparatus, in a\npainter's study.\n\n40.\n\n\"An excellent artist, unfortunately too soon taken from us, Ferdinand\nJagemann, who, with other qualifications, had a fine eye for light and\nshade, colour and keeping, had built himself a painting-room for large\nas well as small works. The single high window was to the north, facing\nthe most open sky, and it was thought that all necessary requisites had\nbeen sufficiently attended to.\n\n\"But after our friend had worked for some time, it appeared to him,\nin painting portraits, that the faces he copied were not equally well\nlighted at all hours of the day, and yet his sitters always occupied\nthe same place, and the serenity of the atmosphere was unaltered.\n\n\"The variations of the favourable and unfavourable light had their\nperiods during the day. Early in the morning the light appeared most\nunpleasantly grey and unsatisfactory; it became better, till at last,\nabout an hour before noon, the objects had acquired a totally different\nappearance. Everything presented itself to the eye of the artist in its\ngreatest perfection, as he would most wish to transfer it to canvas.\nIn the afternoon this beautiful appearance vanished--the light became\nworse, even in the brightest day, without any change having taken place\nin the atmosphere.\n\n\"As soon as I heard of this circumstance, I at once connected it in\nmy own mind with the phenomena which I had been so long observing,\nand hastened to prove, by a physical experiment, what a clear-sighted\nartist had discovered entirely of himself, to his own surprise and\nastonishment.\n\n\"I had the second[5] entoptic apparatus brought to the spot, and the\neffect on this was what might be conjectured from the above statement.\nAt mid-day, when the artist saw his model best lighted, the north,\ndirect reflection gave the white cross; in the morning and evening, on\nthe other hand, when the unfavourable oblique light was so unpleasant\nto him, the cube showed the black cross; in the intermediate hours the\nstate of transition was apparent.\"\n\nThe author proceeds to recall to his memory instances where works of\nart had struck him by the beauty of their appearance owing to the light\ncoming from the quarter opposite the sun, in \"direct reflection,\" and\nadds, \"Since these decided effects are thus traceable to their cause,\nthe friends of art, in looking at and exhibiting pictures, may enhance\nthe enjoyment to themselves and others by attending to a fortunate\nreflection.\"\n\n\n[1] The numbers, as usual, indicate the corresponding paragraphs in the\noriginal.\n\n[2] In the historical part, Goethe has to speak of so many followers of\nNewton who begin their statements with \"Si per foramen exiguum,\" that\nthe term is a sort of by-word with him.\n\n[3] At mid-day on the 24th of June the author observed the white cross\nreflected from every part of the horizon. At a certain distance from\nthe sun, corresponding, he supposes, with the extent of halos, the\nblack cross appeared.\n\n[4] Whence the term _entoptic_.\n\n[5] Before described: the author describes several others more or less\ncomplicated, and suggests a portable one. \"Such plates, which need\nonly be an inch and a quarter square, placed on each other to form a\ncube, might be set in a brass case, open above and below. At one end of\nthis case a black mirror with a hinge, acting like a cover, might be\nfastened. We recommend this simple apparatus, with which the principal\nand original experiment may be readily made. With this we could, in the\nlongest days, better define the circle round the sun where the black\ncross appears,\" &c.\n\n\nNOTE T.--Par. 496.\n\n\"Since Goethe wrote, all the earths have been decomposed, and have\nbeen shown to be metallic bases united with oxygen; but this does not\ninvalidate his statement.\"--S. F.\n\n\nNOTE U.--Par. 502.\n\nThe cold nature of black and its affinity to blue are assumed by the\nauthor throughout; if the quality is opaque, and consequently greyish,\nsuch an affinity is obvious, but in many fine pictures, intense black\nseems to be considered as the last effect of heat, and in accompanying\ncrimson and orange may be said rather to present a difference of\ndegree than a difference of kind. In looking at the great picture\nof the globe, we find this last result produced in climates where\nthe sun has greatest power, as we find it the immediate effect of\nfire. The light parts of black animals are often of a mellow colour;\nthe spots and stripes on skins and shells are generally surrounded\nby a warm hue, and are brown before they are absolutely black. In\ncombustion, the blackness which announces the complete ignition, is\npreceded always by the same mellow, orange colour. The representation\nof this process was probably intended by the Greeks in the black and\nsubdued orange of their vases: indeed, the very colours may have been\nfirst produced in the kiln. But without supposing that they were\nretained merely from this accident, the fact that the combination\nitself is extremely harmonious, would be sufficient to account for\nits adoption. Many of the remarks of Aristotle[1] and Theophrastus[2]\non the production of black, are derived from the observation of the\naction of fire, and on one occasion, the former distinctly alludes to\nthe terracotta kiln. That the above opinion as to the nature of black\nwas prevalent in the sixteenth century, may be inferred from Lomazzo,\nwho observes,--\"Quanto all' origine e generazione de' colori, la\nfrigidità è la madre della bianchezza: il calore è padre del nero.\"[3]\nThe positive coldness of black may be said to begin when it approaches\ngrey. When Leonardo da Vinci says that black is most beautiful in\nshade, he probably means to define its most intense and transparent\nstate, when it is furthest removed from grey.\n\n\n[1] \"De Coloribus.\"\n\n[2] \"De Igne.\"\n\n[3] \"Trattato,\" &c. p. 191, the rest of the passage, it must be\nadmitted, abounds with absurdities.\n\n\n\nNOTE V.--Par. 555.\n\nThe nature of vehicles or liquid mediums to combine with the substance\nof colours, has been frequently discussed by modern writers on art,\nand may perhaps be said to have received as much attention as it\ndeserves. Reynolds smiles at the notion of our not having materials\nequal to those of former times, and indeed, although the methods of\nindividuals will always differ, there seems no reason to suppose that\nany great technical secret has been lost. In these inquiries, however,\nwhich relate merely to the mechanical causes of bright and durable\ncolouring, the skill of the painter in the adequate employment of the\nhigher resources of his art is, as if by common consent, left out of\nthe account, and without departing from this mode of considering the\nquestion, we would merely repeat a conviction before expressed, viz.\nthat the preservation of internal brightness, a quality compatible with\nvarious methods, has had more to do with the splendour and durability\nof finely coloured pictures than any vehicle. The observations that\nfollow are therefore merely intended to show how far the older\nwritten authorities on this subject agree with the results of modern\ninvestigation, without at all assuming that the old methods, if known,\nneed be implicitly followed.\n\nOn a careful examination of the earlier pictures, it is said that\na resinous substance appears to have been mingled with the colours\ntogether with the oil; that the fracture of the indurated pigment is\nshining, and that the surface resists the ordinary solvents.[1] This\nadmixture of resinous solutions or varnishes with the solid is not\nalluded to, as far as we have seen, by any of the writers on Italian\npractice, but as the method corresponds with that now prevalent in\nEngland, the above hypothesis is not likely to be objected to for the\npresent.\n\nVarious local circumstances and relations might seem to warrant the\nsupposition that the Venetian painters used resinous substances. An\nimportant branch of commerce between the mountains of Friuli and Venice\nstill consists in the turpentine or fir-resin.[2] Similar substances\nproduced from various trees, and known under the common name of\nbalsams,[3] were imported from the East through Venice, for general\nuse, before the American balsams[4] in some degree superseded them;\nand a Venetian painter, Marco Boschini, in his description of the\nArchipelago, does not omit to speak of the abundance of mastic produced\nin the island of Scio.[5]\n\nThe testimonies, direct or indirect, against the employment of any\nsuch substances by the Venetian painters, in the solid part of their\nwork, seem, notwithstanding, very conclusive; we begin with the writer\njust named. In his principal composition, a poem[6] describing the\npractice and the productions of the Venetian painters, Boschini speaks\nof certain colours which they shunned, and adds:--\"In like manner\n(they avoided) shining liquids and varnishes, which I should rather\ncall lackers;[7] for the surface of flesh, if natural and unadorned,\nassuredly does not shine, nature speaks as to this plainly.\" After\nalluding to the possible alteration of this natural appearance by\nmeans of cosmetics, he continues: \"Foreign artists set such great\nstore by these varnishes, that a shining surface seems to them the\nonly desirable quality in art. What trash it is they prize! fir-resin,\nmastic, and sandarach, and larch-resin (not to say treacle), stuff fit\nto polish boots.[8] If those great painters of ours had to represent\narmour, a gold vase, a mirror, or anything of the kind, they made it\nshine with (simple) colours.\"[9]\n\nThis writer so frequently alludes to the Flemish painters, of whose\ngreat reputation he sometimes seems jealous, that the above strong\nexpression of opinion may have been pointed at them. On the other hand\nit is to be observed that the term _forestieri_, strangers, does not\nnecessarily mean transalpine foreigners, but includes those Italians\nwho were not of the Venetian state.[10] The directions given by\nRaphael Borghini,[11] and after him by Armenini,[12] respecting the use\nand preparation of varnishes made from the very materials in question,\nmay thus have been comprehended in the censure, especially as some of\nthese recipes were copied and republished in Venice by Bisagno,[13] in\n1642--that is, only six years before Boschini's poem appeared.\n\nRidolfi's Lives of the Venetian Painters[14] (1648) may be mentioned\nwith the two last. His only observation respecting the vehicle is, that\nGiovanni Bellini, after introducing himself by an artifice into the\npainting-room of Antonello da Messina, saw that painter dip his brush\nfrom time to time in linseed oil. This story, related about two hundred\nyears after the supposed event, is certainly not to be adduced as very\nstriking evidence in any way.[15]\n\nAmong the next writers, in order of time prior to Bisagno, may be\nmentioned Canepario[16] (1619). His work, \"De Atramentis\" contains\na variety of recipes for different purposes: one chapter, _De\natramentis diversicoloribus_, has a more direct reference to painting.\nHis observations under this head are by no means confined to the\npreparation of transparent colours, but he says little on the subject\nof varnishes. After describing a mode of preserving white of egg,\nhe says, \"Others are accustomed to mix colours in liquid varnish and\nlinseed, or nut-oil; for a liquid and oily varnish binds the (different\nlayers of) colours better together, and thus forms a very fit glazing\nmaterial.\"[17] On the subject of oils he observes, that linseed oil was\nin great request among painters; who, however, were of opinion that\nnut-oil-excelled it \"in giving brilliancy to pictures, in preserving\nthem better, and in rendering the colours more vivid.\"[18]\n\nLomazzo (a Milanese) says nothing on the subject of vehicles in his\nprincipal work, but in his \"Idea del Tempio della Pittura,\"[19] he\nspeaks of grinding the colours \"in nut-oil, and spike-oil, and other\nthings,\" the \"and\" here evidently means _or_, and by \"other things\" we\nare perhaps to understand other oils, poppy oil, drying oils, &c.\n\nThe directions of Raphael Borghini and Vasari[20] cannot certainly be\nconsidered conclusive as to the practice of the Venetians, but they are\nvery clear on the subject of varnish. These writers may be considered\nthe earliest Italian authorities who have entered much into practical\nmethods. In the few observations on the subject of vehicles in Leonardo\nda Vinci's treatise, \"there is nothing,\" as M. Merimée observes, \"to\nshow that he was in the habit of mixing varnish with his colours.\"\nCennini says but little on the subject of oil-painting; Leon Battista\nAlberti is theoretical rather than practical, and the published\nextracts of Lorenzo Ghiberti's MS. chiefly relate to sculpture.\n\nBorghini and Vasari agree in recommending nut-oil in preference to\nlinseed-oil; both recommend adding varnish to the colours in painting\non walls in oil, \"because the work does not then require to be\nvarnished afterwards,\" but in the ordinary modes of painting on panel\nor cloth, the varnish is omitted. Borghini expressly says, that oil\nalone (senza più) is to be employed; he also recommends a very sparing\nuse of it.\n\nThe treatise of Armenini (1587) was published at Ravenna, and he\nhimself was of Faenza, so that his authority, again, cannot be\nconsidered decisive as to the Venetian practice. After all, he\nrecommends the addition of \"common varnish\" only for the ground or\npreparation, as a consolidating medium, for the glazing colours,\nand for those dark pigments which are slow in drying. Many of his\ndirections are copied from the writers last named; the recipes for\nvarnishes, in particular, are to be found in Borghini. Christoforo\nSorte[21] (1580) briefly alludes to the subject in question. After\nspeaking of the methods of distemper, he observes that the same colours\nmay be used in oil, except that instead of mixing them with size, they\nare mixed on the palette with nut-oil, or (if slow in drying) with\nboiled linseed-oil: he does not mention varnish. The Italian writers\nnext in order are earlier than Vasari, and may therefore be considered\noriginal, but they are all very concise.\n\nThe treatise of Michael Angelo Biondo[22] (1549), remarkable for\nits historical mistakes, is not without interest in other respects.\nThe list of colours he gives is, in all probability, a catalogue of\nthose in general use in Venice at the period he wrote. With regard\nto the vehicle, he merely mentions oil and size as the mediums for\nthe two distinct methods of oil-painting and distemper, and does not\nspeak of varnish. The passages in the Dialogue of Doni[23] (1549),\nwhich relate to the subject in question, are to the same effect. \"In\ncolouring in oil,\" he observes, \"the most brilliant colours (that we\nsee in pictures) are prepared by merely mixing them with the end of a\nknife on the palette.\" Speaking of the perishable nature of works in\noil-painting as compared with sculpture, he says, that the plaster of\nParis (gesso) and mastic, with other ingredients of which the ground\nis prepared, are liable to decay, &c.; and elsewhere, in comparing\npainting in general with mosaic, that in the former the colours \"must\nof necessity be mixed with various things, such as oils, gums, white\nor yolk of egg, and juice of figs, all which tend to impair the beauty\nof the tints.\" This catalogue of vehicles is derived from all kinds of\npainting to enforce the argument, and is by no means to be understood\nas belonging to one and the same method.\n\nAn interesting little work,[24] still in the form of a dialogue (Fabio\nand Lauro), appeared a year earlier; the author, Paolo Pino, was a\nVenetian painter. In speaking of the practical methods Fabio observes,\nas usual, that oil-painting is of all modes of imitation the most\nperfect, but his reasons for this opinion seem to have a reference\nto the Venetian practice of going over the work repeatedly. Lauro\nasks whether it is not possible to paint in oil on the dry wall, as\nSebastian del Piombo did. Fabio answers, \"the work cannot last, for the\nsolidity of the plaster is impenetrable, and the colours, whether in\noil or distemper, cannot pass the surface.\" This might seem to warrant\nthe inference that absorbent grounds were prepared for oil-painting,\nbut there are proofs enough that resins as well as oil were used with\nthe _gesso_ to make the preparation compact. See Doni, Armenini, &c.\nThis writer, again, does not speak of varnish. These appear to be the\nchief Venetian and Italian authorities[25] of the sixteenth and part of\nthe following century; and although Boschini wrote latest, he appears\nto have had 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 allusion to the\nimmixture of varnishes with the solid colours, except in painting on\nwalls in oil, and that the processes of distemper and oil are always\nconsidered as separate arts.[26] On the other hand, the prohibition\nof Boschini cannot be understood to be universal, for it is quite\ncertain that the Venetians varnished their pictures when done.[27]\nAfter Titian had finished his whole-length portrait of Pope Paul III.\nit was placed in the sun to be varnished.[28] Again, in the archives of\nthe church of S. Niccolo at Treviso a sum is noted (Sept. 21, 1521 ),\n\"per far la vernise da invernisar la Pala dell' altar grando,\" and the\nsame day a second entry appears of a payment to a painter, \"per esser\nvenuto a dar la vernise alla Pala,\" &c.[29] It is to be observed that\nin both these cases the pictures were varnished as soon as done;[30]\nthe varnish employed was perhaps the thin compound of naphtha (oglio di\nsasso) and melted turpentine (oglio d'abezzo), described by Borghini,\nand after him by Armenini: the last-named writer remarks that he had\nseen this varnish used by the best painters in Lombardy, and had heard\nthat it was preferred by Correggio. The consequence of this immediate\nvarnishing may have been that the warm resinous liquid, whatever it\nwas, became united with the colours, and thus at a future time the\npigment may have acquired a consistency capable of resisting the\nordinary solvents. Not only was the surface of the picture required to\nbe warm, but the varnish was applied soon after it was taken from the\nfire.[31]\n\nMany of the treatises above quoted contain directions for making the\ncolours dry:[32] some of these recipes, and many in addition, are to be\nfound in Palomino, who, however defective as an historian,[33] has left\nvery copious practical details, evidently of ancient date. His drying\nrecipes are numerous, and although sugar of lead does not appear,\ncardenillo (verdigris), which is perhaps as objectionable, is admitted\nto be the best of all dryers. It may excite some surprise that the\nSpanish painters should have bestowed so much attention on this subject\nin a climate like theirs, but the rapidity of their execution must have\noften required such an assistance.[34]\n\nOne circumstance alluded to by Palomino, in his very minute practical\ndirections, deserves to be mentioned. After saying what colours should\nbe preserved in their saucers under water, and what colours should be\nmerely covered with oiled paper because the water injures them, he\nproceeds to communicate \"a curious mode of preserving oil-colours,\" and\nof transporting them from place to place. The important secret is to\ntie them in bladders, the mode of doing which he enters into with great\nminuteness, as if the invention was recent. It is true, Christoforo\nSorte, in describing his practice in water-colour drawing, says he was\nin the habit of preserving a certain vegetable green with gum-water in\na bladder; but as the method was obviously new to Palomino, there seems\nsufficient reason to believe that oil-colours, when once ground, had,\nup to his time, been kept in saucers and preserved under water.[35]\nAmong the items of expense in the Treviso document before alluded to,\nwe find \"a pan and saucers for the painters.\"[36] This is in accordance\nwith Cennini's directions, and the same system appears to have been\nfollowed till after 1700.[37]\n\nThe Flemish accounts of the early practice of oil-painting are all\nlater than Vasari. Van Mander, in correcting the Italian historian in\nhis dates, still follows his narrative in other respects verbatim. If\nVasari's story is to be accepted as true, it might be inferred that\nthe Flemish secret consisted in an oil varnish like copal.[38] Vasari\nsays, that Van Eyck boiled the oils with other ingredients; that the\ncolours, when mixed with this kind of oil, had a very firm consistence;\nthat the surface of the pictures so executed had a lustre, so that they\nneeded no varnish when done; and that the colours were in no danger\nfrom water.[39]\n\nCertain colours, as is well known, if mixed with oil alone, may be\nwashed off after a considerable time. Leonardo da Vinci remarks, that\nverdigris may be thus removed. Carmine, Palomino observes, may be\nwashed off after six years. It is on this account the Italian writers\nrecommend the use of varnish with certain colours, and it appears the\nVenetians, and perhaps the Italians generally, employed it solely in\nsuch cases. But it is somewhat extraordinary that Vasari should teach\na mode of painting in oil so different in its results (inasmuch as the\nwork thus required varnish at last) from the Flemish method which he so\nmuch extols--a method which he says the Italians long endeavoured to\nfind out in vain. If they knew it, it is evident, assuming his account\nto be correct, that they did not practice it.\n\n\n[1] See \"Marcucci Saggio Analitico-chimico sopra i colori,\" &c. Rome,\n1816, and \"Taylor's Translation of Merimée on Oil-painting,\" London,\n1839. The last-named work contains much useful information.\n\n[2] Italian writers of the 16th century speak of three kinds. Cardanus\nsays, that of the _abies_ was esteemed most, that of the _larix_ next,\nand that of the _picea_ least. The resin extracted by incision from\nthe last (the pinus abies Linnæi) is known by the name of Burgundy\npitch; when extracted by fire it is black. The three varieties occur\nin Italian treatises on art, under the names of _oglio di abezzo_,\n_trementina_ and _pece Greca_.\n\n[3] The concrete balsam _benzoe_, called by the Italians _beluzino_,\nand _belzoino_, is sometimes spoken of as a varnish.\n\n[4] Marcucci supposes that balsam of copaiba was mixed with the\npigments by the (later) Venetians.\n\n[5] \"L'Archipelago con tutte le Isole,\" Ven. 1658. The incidental\nnotices of the remains of antiquity in this work would be curious and\nimportant if they could be relied on. In describing the island of\nSamos, for instance, the author asserts that the temple of Juno was in\ntolerable preservation, and that the statue was still there.\n\n[6] \"La Carta del Navegar Pitoresco,\" Ven. 1660. It is in the Venetian\ndialect.\n\n[7] Inveriadure (invetriature), literally the glazing applied to\nearthenware.\n\n[8]\n\n    \"O de che strazze se fan cavedal!\n    D'ogio d'avezzo, mastici e sandraca;\n    E trementina (per no'dir triaca)\n    Robe, che ilustrerave ogni stival.\"--p. 338.\n\nThe alliteration of the words _trementina_ and _triaca_ is of course\nlost in a translation.\n\n[9] \"I li ha fati straluser co' i colori.\" Boschini was at least\nconstant in his opinion. In the second edition of his \"Ricche Minere\ndella Pittura Veneziana,\" which appeared fourteen years after the\npublication of his poem, he repeats that the Venetian painters avoided\nsome colours in flesh \"e similmente i lustri e le vernici.\"\n\n[10] Thus, in the introduction to the \"Ricche Minere,\" Boschini calls\nthe Milanese, Florentine, Lombard, and Bolognese painters, _forestieri_.\n\n[11] \"Il Riposo,\" Firenze, 1584.\n\n[12] \"De' Veri Precetti della Pittura,\" Ravenna, 1587.\n\n[13] \"Trattato della Pittura fondato nell' autorità di molti eccellenti\nin questa professione.\" Venezia, 1642. Bisagno remarks in his preface,\nthat the books on art were few, and that painters were in the habit of\nkeeping them secret. He acknowledges that he has availed himself of the\nlabours of others, but without mentioning his sources: some passages\nare copied from Lomazzo. He, however, lays claim to some original\nobservations, and says he had seen much and discoursed with many\nexcellent painters.\n\n[14] \"Le Meraviglie dell' Arte,\" Venezia, 1648.\n\n[15] It has been conjectured by some that this story proved the\nimmixture of varnishes with the colours, and that the oil was only used\nto dilute them. The epitaph on Antonello da Messina which existed in\nVasari's time, alludes to his having mixed the colours with oil.\n\n[16] \"Petri Mariæ Caneparii De Atramentis cujuscumque generis,\" Venet.\n1619. It was republished at Rotterdam in 1718.\n\n[17] \"Ita quod magis ex hiis evadit atramentum picturæ summopere\nidoneum.\" Thus, if _atramentum_ is to be understood, as usual, to\nmean a glazing colour, the passage can only refer to the immixture of\nvarnish with the transparent colours applied last in order.\n\n[18] In a passage that follows respecting the mode of extracting\nnut-oil, Caneparius appears to mistranslate Galen, c. 7--\"De Simplicium\nMedicamentorum facultatibus.\" The observations of Galen on this\nsubject, and on the drying property of linseed, may have given the\nfirst hint to the inventors of oil-painting. The custom of dating\nthe origin of this art from Van Eyck is like that of dating the\ncommencement of modern painting from Cimabue. The improver is often\nassumed to be the inventor.\n\n[19] Milan, 1590.\n\n[20] The particulars here alluded to are to be found in the first\nedition of Vasari (1550) as well as the second.--v. i. c. 21, &c.\n\n[21] \"Osservasioni nella Pittura.\" In Venezia, 1580. Sorte, who, it\nappears, was a native of Verona, had worked in his youth with Giulio\nRomano, at Mantua, and communicates the methods taught him by that\npainter, for giving the true effects of perspective in compositions\nof figures. He is, perhaps, the earliest who describes the process of\nwater-colour painting as distinguished from distemper and as adapted to\nlandscape, if the art he describes deserves the name.\n\n[22] \"Della nobilissima Pittura e sua Arte,\" Venezia, 1549. Biondo is\nso ignorant as to attribute the Last Supper, by Leonardo da Vinci, to\nMantegna.\n\n[23] \"Disegno del Doni,\" in Venezia, 1549.\n\n[24] \"Dialogo di Pittura,\" Venezia, 1548. Pino, in enumerating the\ncelebrated contemporary artists, does not include Paul Veronese, for a\nvery obvious reason, that painter being at the time only about 17 years\nof age. Sorte, who wrote thirty years later, mentions \"l'eccellente\nMesser Paulino nostro,\" alone.\n\n[25] The Dialogues of Lodovico Dolce, and various other works, are not\nreferred to here, as they contain nothing on the subject in question.\nThe latest authority at all connected with the traditions of Venetian\npractice, is a certain Giambatista Volpato, of Bassano: he died in\n1706, and had been intimate with Ridolfi. The only circumstance he\nhas transmitted relating to practical details is that Giacomo Bassan,\nin retouching on a dry surface, sometimes adopted a method commonly\npractised, he says, by Paul Veronese (and commonly practised still),\nnamely, that of dipping his brush in spirits of turpentine; at other\ntimes he oiled out the surface in the usual manner. Volpato left a MS.\nwhich was announced for publication in Vicenza in 1685, but it never\nappeared; it, however, afterwards formed the ground-work of Verci's\n\"Notizie intorno alla Vita e alle Opere de' Pittori di Bassano.\"\nVenezia, 1775. See also \"Lettera di Giambatista Roberti sopra Giacomo\nda Ponte,\" Lugano, 1777. Another MS. by Natale Melchiori, of about the\nsame date, is preserved at Treviso and Castel Franco: it abounds with\nhistorical mistakes; the author says, for instance, that the Pietro\nMartyre was begun by Giorgione and finished by Titian. The recipes for\nvarnishes and colours are very numerous, but they are mostly copied\nfrom earlier works.\n\n[26] That distemper was not very highly esteemed by the Venetians\nmay be inferred from the following observation of Pino:--\"Il modo di\ncolorir à guazzo è imperfetto et più fragile et à me non diletta onde\nlasciamolo all' oltremontani i quali sono privi della vera via.\" It is,\nhowever, certain that the Venetians sometimes painted in this style,\nand Volpato mentions several works of the kind by Bassan, but he never\nhints that he began his oil pictures in distemper.\n\n[27] Boschini says, that the Venetians (he especially means Titian)\nrendered their pictures sparkling by finally touching on a dry\nsurface (_à secco_). The absence of varnish in the solid colours, the\nretouching with spirit of turpentine, and even _à secco_, all suppose a\ndull surface, which would require varnish. The latter method, alluded\nto by Boschini, was an exception to the general practice, and not\nlikely to be followed on account of its difficulty. Carlo Maratti, on\nthe authority of Palomino, used to say, \"He must be a skilful painter\nwho can retouch without oiling out.\"\n\n[28] See a letter by Francesco Bocchi, and another by Vasari, in\nthe \"Lettere Pittoriche\" of Bottari. The circumstance is mentioned\nincidentally; the point chiefly dwelt on is, that some persons who\npassed were deceived, and bowed to the picture, supposing it to be the\npope.\n\n[29] Federici, \"Memorie Trevigiane,\" Venezia, 1803. The altar-piece of\nS. Niccolo at Treviso is attributed, in the document alluded to, to\nFra Marco Pensabene, a name unknown; the painting is so excellent as\nto have been thought worthy of Sebastian del Piombo: for this opinion,\nhowever, there are no historical grounds. It was begun in 1520, but\nbefore it was quite finished the painter, whoever he was, absconded: it\nwas therefore completed by another.\n\n[30] Titian's stay in Rome was short, and with respect to the Treviso\naltar-piece, a week or two only, at most, can have elapsed between the\ncompletion and the varnishing. Cennini, who recommends delaying a year\nat least before varnishing, speaks of pictures in distemper.\n\n[31] See Borghini, Armenini, their Venetian copyist Bisagno, and\nPalomino. The last-named writer, though of another school and much\nmore modern, was evidently well acquainted with the ancient methods:\nhe says, \"Se advierte que siempre que se huviere de barnizar alguna\ncosa conviene que la pintura y el barniz estèn calientes.\"--_El Museo\nPictorico_, v. ii.\n\n[32] Burnt alum, one of the ingredients recommended, might perhaps\naccount for a shining fracture in the indurated pigment in some old\npictures.\n\n[33] Of the earlier Spanish writers Pacheco may be mentioned next to\nPalomino as containing most practical information. Carducho, De Butron,\nand others, seldom descend to such details. Palomino contains all the\ndirections of Pacheco, and many in addition.\n\n[34] See Cean Bermudez, \"Sobre la Escuela Sevillana,\" Cadiz, 1806. The\nsame reasons induced the later Venetian machinists to paint on dark\ngrounds, and to make use of (drying) oil in excess. See Zanetti, _Della\nPittura Veneziana_, 1. iv.\n\n[35] Borghini, in describing the method of making a gold-size (the\nsame as Cennini's), speaks of boiling the \"buccie de' colori\" in oil;\nthis only means the skin or pellicle of the colour itself--in fact, he\nproceeds to say that they dissolve in boiling. Vasari, in describing\nthe same process, uses the expression \"colori seccaticci.\"\n\n[36] \"Maggio 4 (1520) Per un cadin (catino) per depentori. Per\nscudellini per li depentori.\"--_Mem. Trev._, vol. i. p. 131. Pungileoni\n(\"Memorie Istoriche di Antonio Allegri\") quotes a note of expenses\nrelating to two oil-pictures by Paolo Gianotti; among the items we find\n\"colori, telari, et brocchette.\"--vol. ii. p. 75.\n\n[37] Salmon, in his \"Polygraphice\" (1701), gives the following\ndirection:--\"Oyl colors, if not presently used, will have a skin grow\nover them, to prevent which put them into a glass, and put the glass\nthree or four inches under water,\" &c.\n\n[38] This varnish appears to have been known some centuries before Van\nEyck's time, but he may have been the first to mix it with the colours.\n\n[39] See Vasari, Life of Antonello da Messina.\n\n\n\nNOTE W.--Par. 608.\n\nIn the second volume Goethe gives the nomenclature of the Greeks and\nRomans at some length. The general notions of the ancients with regard\nto colours are thus described:--\"The ancients derive all colours from\nwhite and black, from light and darkness. They say, all colours are\nbetween white and black, and are mixed out of these. We must not,\nhowever, suppose that they understand by this a mere atomic mixture,\nalthough they occasionally use the word μίξις;[1] for in the remarkable\npassages, where they wish to express a kind of reciprocal (dynamic)\naction of the two contrasting principles, they employ the words κρᾶσις,\nunion, σύγκρισις, combination; thus, again, the mutual influence of\nlight and darkness, and of colours among each other, is described by\nthe word κεράννυστας, an expression of similar import.\n\n\"The varieties of colours are differently enumerated; some mention\nseven, others twelve, but without giving the complete list. From a\nconsideration of the terminology both of the Greeks and Romans, it\nappears that they sometimes employed general for specific terms, and\n_vice versâ_.\n\n\"Their denominations of colours are not permanently and precisely\ndefined, but mutable and fluctuating, for they are employed even with\nregard to similar colours both on the _plus_ and _minus_ side. Their\nyellow, on the one hand, inclines to red, on the other to blue; the\nblue is sometimes green, sometimes red; the red is at one time yellow,\nat another blue. Pure red (purpur) fluctuates between warm red and\nblue, sometimes inclining to scarlet, sometimes to violet.\n\n\"Thus the ancients not only seem to have looked upon colour as a\nmutable and fleeting quality, but appear to have had a presentiment of\nthe (physical and chemical) effects of augmentation and re-action. In\nspeaking of colours they make use of expressions which indicate this\nknowledge; they make yellow redden, because its augmentation tends to\nred; they make red become yellow, for it often returns thus to its\norigin.\n\n\"The hues thus specified undergo new modifications. The colours\narrested at a given point are attenuated by a stronger light darkened\nby a shadow, nay, deepened and condensed in themselves. For the\ngradations which thus arise the name of the species only is often\ngiven, but the more generic terms are also employed. Every colour, of\nwhatever kind, can, according to the same view, be multiplied into\nitself, condensed, enriched, and will in consequence appear more or\nless dark. The ancients called colour in this state,\" &c. Then follow\nthe designations of general states of colour and those of specific hues.\n\nAnother essay on the notions of the ancients respecting the origin\nand nature of colour generally, shows how nearly Goethe himself has\nfollowed in the same track. The dilating effect of light objects,\nthe action and reaction of the retina, the coloured after-image, the\ngeneral law of contrast, the effect of semi-transparent mediums in\nproducing warm or cold colours as they are interposed before a dark or\nlight background--all this is either distinctly expressed or hinted\nat; \"but,\" continues Goethe, \"how a single element divides itself into\ntwo, remained a secret for them. They knew the nature of the magnet,\nin amber, only as attraction; polarity was not yet distinctly evident\nto them. And in very modern times have we not found that scientific\nmen have still given their almost exclusive attention to attraction,\nand considered the immediately excited repulsion only as a mere\nafter-action?\"\n\nAn essay on the Painting of the Ancients[2] was contributed by Heinrich\nMeyer.\n\n\n[1] See Note on Par. 177.\n\n[2] Vol. ii. p. 69, first edition.\n\n\n\nNOTE X.--Par. 670.\n\nThis agrees with the general recommendation so often given by high\nauthorities in art, to avoid a tinted look in the colour of flesh. The\ngreat example of Rubens, whose practice was sometimes an exception\nto this, may however show that no rule of art is to be blindly or\nexclusively adhered to. Reynolds, nevertheless, in the midst of his\nadmiration for this great painter, considered the example dangerous,\nand more than once expresses himself to this effect, observing on one\noccasion that Rubens, like Baroccio, is sometimes open to the criticism\nmade on an ancient painter, namely, that his figures looked as if they\nfed on roses.\n\nLodovico Dolce, who is supposed to have given the _vivâ voce_ precepts\nof Titian in his Dialogue,[1] makes Aretino say: \"I would generally\nbanish from my pictures those vermilion cheeks with coral lips; for\nfaces thus treated look like masks. Propertius, reproving his Cynthia\nfor using cosmetics, desires that her complexion might exhibit the\nsimplicity and purity of colour which is seen in the works of Apelles.\"\n\nThose who have written on the practice of painting have always\nrecommended the use of few colours for flesh. Reynolds and others quote\neven ancient authorities as recorded by Pliny, and Boschini gives\nseveral descriptions of the method of the Venetians, and particularly\nof Titian, to the same effect. \"They used,\" he says, \"earths more than\nany other colour, and at the utmost only added a little vermilion,\nminium, and lake, abhorring as a pestilence _biadetti, gialli santi,\nsmaltini, verdi-azzurri, giallolini_.\"[2] Elsewhere he says,[3] \"Earths\nshould be used rather than other colours:\" after repeating the above\nprohibited list he adds, \"I speak of the imitation of flesh, for in\nother things every colour is good;\" again, \"Our great Titian used to\nsay that he who wishes to be a painter should be acquainted with three\ncolours, white, black, and red.\"[4] Assuming this account to be a\nlittle exaggerated, it is still to be observed that the monotony to\nwhich the use of few colours would seem to tend, is prevented by the\nnature of the Venetian process, which was sufficiently conformable to\nGoethe's doctrine; the gradations being multiplied, and the effect\nof the colours heightened by using them as semi-opaque mediums.\nImmediately after the passage last quoted we read, \"He also gave this\ntrue precept, that to produce a lively colouring in flesh it is not\npossible to finish at once.\"[5] As these particulars may not be known\nto all, we add some further abridged extracts explaining the order and\nmethods of these different operations.\n\n\"The Venetian painters,\" says this writer,[6] \"after having drawn in\ntheir subject, got in the masses with very solid colour, without making\nuse of nature or statues. Their great object in this stage of their\nwork was to distinguish the advancing and retiring portions, that the\nfigures might be relieved by means of chiaro-scuro--one of the most\nimportant departments of colour and form, and indeed of invention.\nHaving decided on their scheme of effect, when this preparation was\ndry, they consulted nature and the antique; not servilely, but with the\naid of a few lines on paper (_quattro segni in carta_) they corrected\ntheir figures without any other model. Then returning to their brushes,\nthey began to paint smartly on this preparation, producing the colour\nof flesh.\" The passage before quoted follows, stating that they used\nearths chiefly, that they carefully avoided certain colours, \"and\nlikewise varnishes and whatever produces a shining surface.[7] When\nthis second painting was dry, they proceeded to scumble over this or\nthat figure with a low tint to make the one next it come forward,\ngiving another, at the same time, an additional light--for example, on\na head, a hand, or a foot, thus detaching them, so to speak, from the\ncanvas.\" (Tintoret's _Prigionia di S. Rocco_ is here quoted.) \"By thus\nstill multiplying these well-understood retouchings where required, on\nthe dry surface, _(à secco)_ they reduced the whole to harmony. In this\noperation they took care not to cover entire figures, but rather went\non gemming them _(gioielandole)_ with vigorous touches. In the shadows,\ntoo, they infused vigour frequently by glazing with asphaltum, always\nleaving great masses in middle-tint, with many darks, in addition to\nthe partial glazings, and few lights.\"\n\nThe introduction to the subject of Venetian colouring, in the poem by\nthe same author, is also worth transcribing, but as the style is quaint\nand very concise, a translation is necessarily a paraphrase.[8]\n\n\"The art of colouring has the imitation of qualities for its object;\nnot all qualities, but those secondary ones which are appreciable by\nthe sense of sight. The eye especially sees colours, the imitation\nof nature in painting is therefore justly called colouring; but the\npainter arrives at his end by indirect means. He gives the varieties\nof tone in masses;[9] he smartly impinges lights, he clothes his\npreparation with more delicate local hues, he unites, he glazes: thus\neverything depends on the method, on the process. For if we look\nat colour abstractedly, the most positive may be called the most\nbeautiful, but if we keep the end of imitation in view, this shallow\nconclusion falls to the ground. The refined Venetian manner is very\ndifferent from mere direct, sedulous imitation. Every one who has\na good eye may arrive at such results, but to attain the manner of\nPaolo, of Bassan, of Palma, Tintoret, or Titian, is a very different\nundertaking.\"[10]\n\nThe effects of semi-transparent mediums in some natural productions\nseem alluded to in the following passage--\"Nature sometimes\naccidentally imitates figures in stones and other substances, and\nalthough they are necessarily incomplete in form, yet the principle\nof effect (depth) resembles the Venetian practice.\" In a passage that\nfollows there appears to be an allusion to the production of the\natmospheric colours by semi-transparent mediums.[11]\n\n\n[1] \"Dialogo della Pittura, intitolato l'Aretino.\" It was first\npublished at Venice in 1557; about twenty years before Titian's death.\nIn the dedication to the senator Loredano, Lodovico Dolce eulogises\nthe work, which he would hardly have done if it had been entirely his\nown: again, the supposition that it may have been suggested by Aretino,\nwould be equally conclusive, coupled with internal evidence, as to the\noriginal source.\n\n[2] Introduction to the \"Ricche Minere della Pittura Veneziana,\"\nVenezia, 1674. The Italian annotators on older works on painting are\nsometimes at a loss to find modern terms equivalent to the obsolete\nnames of pigments. (See \"Antologia dell 'Arte Pittorica.\") The colours\nnow in use corresponding with Boschini's list, are probably yellow\nlakes, smalt, verditer, and Naples yellow. Boschini often censures the\npractice of other schools, and in this emphatic condemnation he seems\nto have had an eye to certain precepts in Lomazzo, and perhaps, even\nin Leonardo da Vinci, who, on one occasion, recommends Naples yellow,\nlake, and white for flesh. The Venetian writer often speaks, too, in\nno measured terms of certain Flemish pictures, probably because they\nappeared to him too tinted.\n\n[3] \"La Carta del Navegar Pitoresco,\" p. 338.\n\n[4] Ib. p. 341. In describing Titian's actual practice (\"Ricche\nMinere\"), he, however, adds yellow (ochre). The red is also\nparticularised, viz., the common terra rossa.\n\n[5] High examples here again prove that the opposite system may attain\nresults quite as successful.\n\n[6] Introduction to the \"Ricche Minere.\"\n\n[7] See Note to Par. 555. Here again, assuming the description to be\ncorrect, high authorities might be opposed to the Venetians.\n\n[8] The following quatrain may serve as a specimen; the author is\nspeaking of the importance of the colour of flesh as conducive to\npicturesque effect:--\n\n    \"Importa el nudo; e come ben l'importa!\n    Un quadro senta nudo è come aponto\n    Un disnar senza pan, se ben ghe zonto,\n    Per più delicia, confetura e torta.\"--p. 346.\n\nIn his preface he anticipates, and thus answers the objections to his\nVenetian dialect--\"Mi, che son Venetian in Venetia e che parlo de'\nPitori Venetiani hò da andarme a stravestir? Guarda el Cielo.\"\n\n[9] The word _Macchia_, literally a blot, is generally used by Italian\nwriters, by Vasari for instance, for the local colour. Boschini\nunderstands by it the relative depth of tones rather than the mere\ndifference of hue. \"By macchia,\" he says, \"I understand that treatment\nby which the figures are distinguished from each other by different\ntones lighter or darker.\"--_La Carta del Navegar_, p. 328. Elsewhere,\n\"Colouring (as practised by the Venetians) comprehends both the macchia\nand drawing;\" (p. 300) that is, comprehends the gradations of light\nand dark in objects, and the parts of objects, and consequently, their\nessential form. \"The macchia,\" he adds, \"is the effect of practice, and\nis dictated by the knowledge of what is requisite for effect.\"\n\n[10]\n\n    \"Ma l'arivar a la maniera, al trato\n    (Verbi gratia) de Paulo, del Bassan,\n    Del Vechio, Tentoreto, e di Tician,\n    Per Dio, l'è cosa da deventar mato.\"--p. 294, 297.\n\n\n[11] The traces of the Aristotelian theory are quite as apparent in\nBoschini as in the other Italian writers on art; but as he wrote in the\nseventeenth century, his authority in this respect is only important as\nan indication of the earlier prevalence of the doctrine.\n\n\n\nNOTE Y.--Par. 672.\n\nThe author's conclusion here is unsatisfactory, for the colour of\nthe black races may be considered at least quite as negative as that\nof Europeans. It would be safer to say that the white skin is more\nbeautiful than the black, because it is more capable of indications\nof life, and indications of emotion. A degree of light which would\nfail to exhibit the finer varieties of form on a dark surface, would\nbe sufficient to display them on a light one; and the delicate\nmantlings of colour, whether the result of action or emotion, are more\nperceptible for the same reason.\n\n\n\nNOTE Z.--Par. 690.\n\nThe author appears to mean that a degree of brightness which the organ\ncan bear at all, must of necessity be removed from dazzling, white\nlight. The slightest tinge of colour to this brightness, implies that\nit is seen through a medium, and thus, in painting, the lightest,\nwhitest surface should partake of the quality of depth. Goethe's view\nhere again accords, it must be admitted, with the practice of the best\ncolourists, and with the precepts of the highest authorities.--See Note\nC.\n\n\n\nNOTE A A.--Par. 732.\n\nAmple details respecting the opinions of Louis Bertrand Castel, a\nJesuit, are given in the historical part. The coincidence of some\nof his views with those of Goethe is often apparent: he objects,\nfor instance, to the arbitrary selection of the Newtonian spectrum;\nobserving that the colours change with every change of distance between\nthe prism and the recipient surface.--_Farbenl._ vol. ii. p. 527.\nJeremias Friedrich Gülich was a dyer in the neighbourhood of Stutgardt:\nhe published an elaborate work on the technical details of his own\npursuit.--_Farbenl._ vol. ii. p. 630.\n\n\n\nNOTE B B.--Par. 748.\n\nGoethe, in his account of Castel, suppresses the learned Jesuit's\nattempt at colorific music (the claveçin oculaire), founded on the\nNewtonian doctrine. Castel was complimented, perhaps ironically, on\nhaving been the first to remark that there were but three principal\ncolours. In asserting his claim to the discovery, he admits that there\nis nothing new. In fact, the notion of three colours is to be found in\nAristotle; for that philosopher enumerates no more in speaking of the\nrainbow,[1] and Seneca calls them by their right names.[2] Compare with\nDante, Parad. c. 33. The relation between colours and sounds is in like\nmanner adverted to by Aristotle; he says--\"It is possible that colours\nmay stand in relation to each other in the same manner as concords\nin music, for the colours which are (to each other) in proportions\ncorresponding with the musical concords, are those which appear to\nbe the most agreeable.\"[3] In the latter part of the 16th century,\nArcimboldo, a Milanese painter, invented a colorific music; an account\nof his principles and method will be found in a treatise on painting\nwhich appeared about the same time. \"Ammaestrato dal quai ordine Mauro\nCremonese dalla viola, musico dell' Imperadore Ridolfo II. trovò sul\ngravicembalo tutte quelle consonanze che dall' Arcimboldo erano segnate\ncoi colori sopra una carta.\"[4]\n\n[1] \"De Meteor.,\" lib. 3, c. ii. and iv. He observes that this is the\nonly effect of colour which painters cannot imitate.\n\n[2] \"De Ignib. cœlest.\" The description of the prism by Seneca is\nanother instance of the truth of Castel's admission. The Roman\nphilosopher's words are--\"Virgula solet fieri vitrea, stricta vel\npluribus angulis in modo clavæ tortuosæ; hæc si ex transverso solem\naccipit colorem talem qualis in arcu videri solet, reddit,\" &c.\n\n[3] \"De Sensu et sensili.\"\n\n[4] \"Il Figino, overo del Fine della Pittura,\" Mantova, 1591, p. 249.\nAn account of the absurd invention of the same painter in composing\nfigures of flowers and animals, and even painting portraits in this\nway, to the great delight of the emperor, will be found in the same\nwork.\n\n\n\nNOTE C C.--Par. 758.\n\nThe moral associations of colours have always been a more favourite\nsubject with poets than with painters. This is to be traced to the\nmaterials and means of description as distinguished from those of\nrepresentation. An image is more distinct for the mind when it is\ncompared with something that resembles it. An object is more distinct\nfor the eye when it is compared with something that differs from it.\nAssociation is the auxiliary in the one case, contrast in the other.\nThe poet, of necessity, succeeds best in conveying the impression\nof external things by the aid of analogous rather than of opposite\nqualities: so far from losing their effect by this means, the images\ngain in distinctness. Comparisons that are utterly false and groundless\nnever strike us as such if the great end is accomplished of placing\nthe thing described more vividly before the imagination. In the common\nlanguage of laudatory description the colour of flesh is like snow\nmixed with vermilion: these are the words used by Aretino in one of\nhis letters in speaking of a figure of St. John, by Titian. Similar\ninstances without end might be quoted from poets: even a contrast can\nonly be strongly conveyed in description by another contrast that\nresembles it.[1] On the other hand it would be easy to show that\nwhenever poets have attempted the painter's method of direct contrast,\nthe image has failed to be striking, for the mind's eye cannot see the\nrelation between two colours.\n\nUnder the same category of effect produced by association may be\nclassed the moral qualities in which poets have judiciously taken\nrefuge when describing visible forms and colours, to avoid competition\nwith the painters' elements, or rather to attain their end more\ncompletely. But a little examination would show that very pleasing\nmoral associations may be connected with colours which would be far\nfrom agreeable to the eye. All light, positive colours, light-green,\nlight-purple, white, are pleasing to the mind's eye, and no degree\nof dazzling splendour is offensive. The moment, however, we have to\ndo with the actual sense of vision, the susceptibility of the eye\nitself is to be considered, the law of comparison is reversed, colours\nbecome striking by being opposed to what they are not, and their moral\nassociations are not owing to the colours themselves, but to the\nmodifications such colours undergo in consequence of what surrounds\nthem. This view, so naturally consequent on the principles the author\nhas himself arrived at, appears to be overlooked in the chapter under\nconsideration, the remarks in which, in other respects, are acute and\ningenious.\n\n\n[1] Such as--\n\n    \"Her beauty hangs upon the cheek of night,\n    Like a rich jewel in an Ethiop's ear.\"\n                          _Romeo and Juliet_.\n\n\n\n\nNOTE D D.--Par. 849.\n\nAccording to the usual acceptation of the term chiaro-scuro in the\nartist world, it means not only the mutable effects produced by light\nand shade, but also the permanent differences in brightness and\ndarkness which are owing to the varieties of local colour.\n\n\n\nNOTE E E.--Par. 855.\n\nThe mannered treatment of light and shade here alluded to by the\nauthor is very seldom to be met with in the works of the colourists;\nthe taste may have first arisen from the use of plaster-casts, and\nwas most prevalent in France and Italy in the early part of the last\ncentury. Piazzetta represented it in Venice, Subleyras in Rome. In\nFrance \"Restout taught his pupils that a globe ought to be represented\nas a polyhedron. Greuze most implicitly adopted the doctrine, and in\npractice showed that he considered the round cheeks of a young girl or\nan infant as bodies cut into facettes.\"[1]\n\n\n[1] See Taylor's translation of Merimée on oil-painting, p. 27.\nBarry, in a letter from Paris, speaks of Restout as the only painter\nwho resembled the earlier French masters: the manner in question is\nundoubtedly sometimes very observable in Poussin. The English artist\nelsewhere speaks of the \"broad, happy manner of Subleyras.\"--_Works_,\nLondon, 1809.\n\n\n\nNOTE F F.--Par. 859.\n\nAll this was no doubt suggested by Heinrich Meyer, whose chief\noccupation in Rome, at one time, was making sepia drawings from\nsculpture (see Goethe's Italiänische Reise). It is hardly necessary to\nsay that the observation respecting the treatment of the surface in the\nantique statues is very fanciful.\n\n\n\nNOTE G G.--Par. 863.\n\nThis observation might have been suggested by the drawings of Claude,\nwhich, with the slightest means, exhibit an harmonious balance of warm\nand cold.\n\n\n\nNOTE H H.--Par. 865.\n\nThe colouring of Paolo Uccello, according to Vasari's account of him,\nwas occasionally so remarkable that he might perhaps have been fairly\nincluded among the instances of defective vision given by the author.\nHis skill in perspective, indicating an eye for gradation, may be also\nreckoned among the points of resemblance (see Par. 105).\n\n\n\nNOTE I I.--Par. 902.\n\nThe quotation before given from Boschini shows that the method\ndescribed by the author, and which is true with regard to some of the\nFlorentine painters, was not practised by the Venetians, for their\nfirst painting was very solid. It agrees, however, with the manner\nof Rubens, many of whose works sufficiently corroborate the account\nof his process given by Descamps. \"In the early state of Rubens's\npictures,\" says that writer,[1] \"everything appeared like a thin wash;\nbut although he often made use of the ground in producing his tones,\nthe canvas was entirely covered more or less with colour.\" In this\nsystem of leaving the shadows transparent from the first, with the\nground shining through them, it would have been obviously destructive\nof richness to use white mixed with the darks, the brightness, in\nfact, already existed underneath. Hence the well-known precept of\nRubens to avoid white in the shadows, a precept, like many others,\nbelonging to a particular practice, and involving all the conditions of\nthat practice.[2] Scarmiglione, whose Aristotelian treatise on colour\nwas published in Germany when Rubens was three-and-twenty, observes,\n\"Painters, with consummate art, lock up the bright colours with dark\nones, and, on the other hand, employ white, the poison of a picture,\nvery sparingly.\" (Artificiosissimè pictores claros obscuris obsepiant\net contra candido picturarum veneno summè parcentes, &c.)\n\n\n[1] \"La Vie des Peintres Flamands,\" vol. i.\n\n[2] The method he recommended for keeping the colours pure in the\nlights, viz. to place the tints next each other unmixed, and then\nslightly to unite them, may have degenerated to a methodical manner\nin the hands of his followers. Boschini, who speaks of Rubens himself\nwith due reverence, and is far from confounding him with his imitators,\ncontrasts such a system with that of the Venetians, and adds that\nTitian used to say, \"Chi de imbratar colori teme, imbrata e machia\nsi medemi.\"--_Carta del Navegar_, p. 341. The poem of Boschini is in\nmany respects polemical. He wrote at a time when the Flemish painters,\nhaving adopted and modified the Venetian principles, threatened to\nsupersede the Italian masters in the opinion of the world. Their\nexcellence, too, had all the charm of novelty, for in the seventeenth\ncentury Venice produced no remarkable talent, and it was precisely\nthe age for her to boast of past glories. The contemptuous manner in\nwhich Boschini speaks of the Flemish varnishes, of the fear of mixing\ntints, &c., is thus always to be considered with reference to the time\nand circumstances. So also his boasting that the Venetian masters\npainted without nature, which may be an exaggeration, is pointed at\nthe _Naturalisti_, Caravaggio and his followers, who copied nature\nliterally.\n\n\n\nNOTE K K.--Par. 903.\n\nThe practice here alluded to is more frequently observable in slight\nworks by Paul Veronese. His ground was often pure white, and in some\nof his works it is left as such. Titian's white ground was covered\nwith a light warm colour, probably at first, and appears to have\nbeen similar to that to which Armenini gives the preference, namely,\n\"quella che tira al color di carne chiarissima con un non so che di\nfiammeggiante.\"[1]\n\n\n[1] \"Veri Precetti della Pittura,\" p. 123.\n\n\nNOTE L L.--Par. 919.\n\nThe notion which the author has here ventured to express may have\nbeen suggested by the remarkable passage in the last canto of Dante's\n\"Paradiso\"--\n\n    \"Nella profonda e chiara sussistenza,\n    Dell' alto lume parremi tre giri\n    Di tre colori e d'una continenza,\" &c.\n\nAfter the concluding paragraph the author inserts a letter from a\nlandscape-painter, Philipp Otto Runge, which is intended to show that\nthose who imitate nature may arrive at principles analogous to those of\nthe \"Farbenlehre.\"\n\n\n## THE END.\n\n\n\n\n\n\nEnd of the Project Gutenberg EBook of Goethe's Theory of Colours, by\nJohann, Wolfgang von Goethe\n\n\n*** END OF THE PROJECT GUTENBERG EBOOK 50572 ***",
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