23. Hermann Helmholtz

Today's German physicists agree that it is the greatest among them who closed his eyes forever on September 8, 1894. For decades, wide circles of educated people have become accustomed to turning primarily to the writings of two outstanding contemporaries when they need advice on the two most important questions that the contemplation of nature awakens in every thinking person. Those who thirst to learn something about how living beings, including man, have come into being and developed, should consult the works of Ernst Haeckel; those who ponder the effects of nature on man's senses will find the most varied inspiration in the works of Hermann Helmholtzens. These two men are the embodiment of our current understanding of nature. The one endeavored to solve the riddle of the becoming of living beings; the other immersed himself in what had become and traced the laws of its action. Few researchers have succeeded in having their achievements recognized to such a high degree during their lifetime as Hermann Helmholtz. Tributes and awards poured in from all over the world when he celebrated his seventieth birthday three years ago. Such a rare success is astonishing when one considers the difficulties with which the pioneers of science often have to struggle, especially when, like Helmholtz, they disdain to step out of the circle of their scientific work and take part in branches of public life in which there is more interest than in strict science. The astonishment disappears as soon as one takes a look at the historical position of the deceased researcher within the scientific development of the last century. Helmholtz's youth was a time that was richer than any other in burning scientific questions. He found a myriad of tasks that were in such a state that the solution could be expected any day. The methods of research were so well developed that in many cases only a small step was needed to achieve epoch-making discoveries on the paths already taken. The great stimulus in the field of natural science in Germany is Johannes Müller, the teacher of Helmholtz and Haeckel and many others with whose names the modern view of nature is associated. All those who were present at the celebration of Ernst Haeckel's sixtieth birthday in Jena on February 17, 1894, will never forget the enthusiasm with which this researcher spoke the words with which he described the influence that Johannes Müller had exerted on him: "I had already heard comparative anatomy ... and came, so well prepared, to the lectures of Johannes Müller, a man whose extraordinary greatness and majesty are still vivid in my mind today. Now, when I occasionally tire at work, I need only look at the picture of Johannes Müller hanging in front of me in my study to gain new strength. ... He taught comparative anatomy and physiology. ... I had such reverence for his formidable personality that I did not dare to approach him. ... It happened to me several times that I wanted to ask him for advice. My heart pounding, I climbed the stairs, touched the doorbell, but didn't dare ring it and turned back." This is how his students describe the man who initiated the scientific movement within which Helmholtz achieved his great successes. Johannes Müller purged science of a whole series of prejudices in order to clear the way for a sober, but unbiased view of the processes in the animal and human organism. He took up the fight against the short-sighted view that assumes two fundamentally different explanatory principles for inorganic and organic nature, between which mediation is supposed to be absolutely impossible. To explain inorganic nature, this view assumed the mechanical, chemical and physical forces; to elucidate the phenomena of organic life, it believed that a special "life force" was required, of which, however, a clear conception is impossible. The extension of the physical approach and its methods to the study of living nature forms the basic feature of the so-called "scientific age", which began with Johannes Müller. Helmholtz's research results bear the hallmark of this age in the most perfect way. Any scientific assumption that contradicts the laws of mechanical physics is unjustified: that was the end of his thinking. Whoever speaks of a "life force" turns the organism into a perpetual motion machine, a self-moving mover. He makes the force necessary for organic movement spring from nothing. This is impossible. Every form of force can only arise from another through transformation. There is one unchangeable quantity of force in the universe, and all kinds of forces, organic as well as inorganic, can only be forms of this one force. Where force arises, it must emerge from the transformation of a corresponding quantity of a different kind of force. This is the now famous "law of the conservation of force", which Helmholtz defended before the members of the Berlin Academy of Sciences in 1847. The fact that the establishment of this law was in the truest sense of the word a requirement of the view of the times is proven by the fact that it was also discovered at the same time by Julius Robert Mayer from Württemberg. The application of the physical research method to the processes of organic life led Helmholtz to the idea of determining the speed at which a stimulus exerted on a nerve propagates in the organism. The fact that he succeeded in this was a success for the physical school of thought. It was proof that the processes inside and outside the organism could be measured.

Helmholtz also used the same physical method to research the laws according to which our senses convey our perception of the outside world. Johannes Müller had also paved the way in this field. He was the originator of the view that the type of sensation that an external impression makes on us depends on the sensory nerves through which it is conveyed. If the optic nerve is stimulated, the sensation of light arises, regardless of whether light or electric current or pressure acts on the eye. This theorem drew the attention of natural scientists to the mechanism of the sensory organs. Helmholtz found a fruitful field of work here. A momentous invention in this field made him a famous man in one fell swoop. It is the ophthalmoscope, through which the images on the retina in the eye and parts of this retina itself can be observed. Helmholtz also found everything ready for this invention. Brücke, also a student of Johannes Müller, had been working on the theory of ocular luminosity, which is based on the fact that part of the light that falls on the retina is reflected back outwards. Brücke had only neglected to ask himself which optical image the light returning from the eye belonged to. Helmholtz came across this question when he was considering how he could best teach his students Brücke's theory of ocular luminosity. The answer to this question also provided the instrument that would allow us to look inside the human eye and thus open up new avenues in ophthalmology. Helmholtz thus proved that modern natural science must also satisfy those who agree with Bacon of Verulam, the father of empirical science, and believe that science should draw its knowledge from life in order to make it practically applicable to life. The construction of the eye mirror was decisive for his external position in the world. He now found no obstacle to carrying out his great plans concerning the physiology of the sensory organs. He set out the functions of the eye and the ear in two extensive works. He shed new light on long-known facts and improved inadequate methods. When it came to filling gaps in research left open by his predecessors with new equipment, his ingenuity never let him down. In this way, in his "Physiological Optics" and in his "Doctrine of the Sensations of Sound", he produced works that have become fundamental to the fields of knowledge to which they belong. He subjected the processes in the eye under the influence of external objects and after the removal of the external influence to a precise investigation; for the perception of colors and color nuances he devised ingenious hypotheses based on the views of Th. Young. Some of his explanations are no longer tenable in the light of our present experience; but everyone who enters this field of research first seeks to gain a position in relation to Hermann Helmholtz's views. Proof of this is the recently published "Theory of Color Vision" by Ebbinghaus. No one contradicted Helmholtz without first expressing their appreciation of his achievements.

Helmholtz's explanation of the nature of timbre in his "Theory of the Sensations of Tone" had the effect of enlightenment. Helmholtz had deduced from observations first made by G. S. Ohm that the so-called tones of the violin, piano and so on, and even those of the human voice, are not simple tones at all, but sound phenomena composed of one tone with its numerous overtones. By taking into account the experience that microscopists had gained about the structure of the ear, he succeeded in gaining an understanding of how the organ of hearing breaks down the composite elements back into their constituent elements and in this way conveys the perception of timbre to consciousness. Helmholtz explains the appearance of chords by the occurrence of so-called beats when two tones of different pitches are sounded simultaneously, which consist in the alternating rise and fall of the tone strengths. With this work, Helmholtz wanted to provide a physiological basis for music aesthetics. How well he knew that aesthetics had an independent field alongside natural science, which he himself did not want to enter, is demonstrated by his words in the final chapter of the book, where he says with regard to the questions that lie beyond physiology: "Admittedly, the more interesting part of musical aesthetics only begins here - after all, it is a matter of finally explaining the wonders of the great works of art, of getting to know the expressions and movements of the various moods of the soul. However tempting the goal may be, I prefer to leave these investigations, in which I would feel too much like a dilettante, to others and remain myself on the ground of natural research to which I am accustomed." These words should be heeded by those who believe that all salvation must come from natural science, and for whom all intellectual courage immediately fades if they do not have the solid ground of experimental facts under their feet.

The inner circle of mathematical physicists and mathematicians also regarded Hermann Helmholtz as a leading spirit in his field of knowledge. He succeeded in solving problems on which Euler and Lagrange had tried their ingenuity in vain. He found answers in many things where others only clearly recognized that there was a question. He who works in this way satisfies many, because he frees them from the nightmare of agonizing riddles. Some of Johannes Müller's enormous demands have been fulfilled today. Helmholtz is the greatest of those who have worked on this fulfillment. He was one of the best of his time because he understood his tasks like few others. His views on art were rooted in the soil of classicism. In his "Doctrine of the Sensations of Sound", he wanted to create a scientific basis for classical music. This did not prevent him from fully understanding Richard Wagner's genius. We younger people need not be deceived by the fact that we can no longer share Helmholtz's views in many areas. A new view of art, a new philosophy fills us, and these will also have a new view of nature in their wake, which will break with much that is associated with Helmholtz's name. But every view of the times gives rise to achievements that are everlasting, and these include those that Helmholtz incorporated into science out of the character of his time.