HELMHOLTZ.1 By T. C. MENDENHALL. Hermann Ludwig Ferdinand, Baron von Helmholtz, was born in Potsdam on August 31, 1821. In 1842 he received his degree in medicine at Berlin, and entered the Government service as an army surgeon. In 1847 he published his essay on the Conservation of Energy. In 1849 he was appointed professor of physiology at Bonn. In 1851 he invented the ophthalmoscope. In 1855 he was made professor of anatomy and physiology at Bonn. In 1859 he was appointed to the same chair at Heidelberg. In 1860 he was made one of the foreign members of the Royal Society of London. In 1863 he published his great work on the Sensations of Tone. In 1866 the first edition of his Physiological Optics was completed. In 1871 he was made professor of natural philosophy at the University of Berlin. In 1873 he received from the Royal Society the highest distinction which it can bestow, the Copley Medal; and in the same year the King of Prussia conferred upon him the Order of Merit in Science and Art. In 1883 hereditary nobility was conferred upon him by Emperor William I. In 1887 he assumed the directorship of the great Physico-Technical Institute, founded by the German Government at Charlottenberg. In 1891 the seventieth anniversary of his birth was celebrated with great ceremony, and he was placed at the head of the civil list by the German Emperor. In 1893 he visited America, serving as president of the International Electrical Congress held in Chicago. In 1894, on September 8, he died at the age of 73 years. Such is the brief outline of the life of one of the most extraordinary men of the present century. To perfect such a sketch in anything like just proportions, or to attempt in the few minutes allotted to me to night to set forth anything like a fair estimate of the labors of one of whom it may be justly said that he was the most accomplished scholar of modern times, is a task no one would seek. Nor can one easily decline the honor which is carried by an invitation from a commission representing the scientific societies of Washington to take part in so memorable a commemoration as this. Under the circumstances, I must 1 Read at a memorial meeting under the auspices of the Joint Commission of the Scientific Societies at Washington City, Jannary 14, 1896. Reprinted from Scieuse. New series, Vol. III, No. 5, February 7, 1896. confine myself to an exposition, all too brief, of a few only of the principal contributions to human knowledge among the great number for which the world is indebted to Professor Helmholtz. It was his distinctive characteristic that among the exponents of modern science he stood quite alone in being really great along several lines. He was in the beginning and always a pure mathematician of high type. Anatomists and physiologists claimed him for their own. During a few days' stay in New York in 1893, after having presided over the International Congress of Electricians, he was entertained by a distinguished surgeon, the leading eye specialist of the country, and ophthalmologists flocked to do him honor as one of the founders of their profession. When, in 1881, he gave the Faraday lecture before the Chemical Society of London, the president of the society in presenting to him the Faraday Medal, declared that eminent as was Helmholtz as an anatomist, a physiologist, a physicist, and a mathematician, he was distinctly claimed by the chemists. Nor were these only idle compliments. Only a few days ago I happened on a most curious and interesting illustration of the unequaled extent of his scientific constituency in finding, in a widely known journal published in London, his obituary notice indexed under the heading, "The stage and music," where his name appeared accompanied by only that of Anton Rubenstein. His great work on the Sensations of Tone and his analysis of the vowel sounds of the human voice gave him a lasting fame among musicians. Psychology as well as aesthetics was benefited by his touch, but I think it will be generally admitted that he was first of all, and more than all else, a physicist. Indeed, it may be said that the best fruits of his study of other branches of science grew out of the skill with which he ingrafted upon them the methods of investigation for which we are primarily indebted to the physicist. When a boy he had acquired a fondness for the study of nature. His father was a professor of literature in the gymnasium at Potsdam; his mother a woman of English descent. Although he was encouraged in the development of his youthful tastes as much as possible, the necessity for earning a living directed his professional studies toward medicine and he became a military surgeon. As a physiologist, he was led to the study of "vital force;" his taste for mathematics and physics forced him to the dynamical point of view, and his first great paper, prepared before he was 26 years of age, was on the Conservation of Energy. It is now nearly fifty years since this essay was presented to the Physical Society of Berlin, and doubtless quite fifty years since it was actually worked out. Its excellence is shown by the fact that if rewritten to-day it would be changed only a little in its nomenclature. Fifty years ago the great law of the conservation of energy, which will ever be regarded as the most pregnant and far-reaching generalization of this century, was so far from being known or recognized that many of the ablest men of the time either regarded it as a "fanciful speculation"-or did not regard it at all. As a matter of ordinary mechanics, it had long been admitted that no machine could create power, and as a part of that applied was always lost or frittered away in friction the work coming out of a machine must always be less than that put into it. The first great advance had been made by an American, Benjamin Thompson, afterwards Count Rumford, when he asked what became of that part lost in friction and found his answer in the heat generated thereby, thus proving that "heat was a mode of motion" rather than an "imponderable agent," as it was rather ambiguously designated up to nearly the middle of this century, but that all of the forces of nature were so related to each other as to be interconvertible, and that the sum total of all the energies of the universe was always the same, energy being no more capable of creation or destruction than matter; these were great facts, mere glimpses of which had been permitted to the physi cists of the early part of the century. Helmholtz was certainly one of the first to completely grasp this splendid generalization, and not more than two or three others stand with him in the credit which is due for its complete proof and general acceptance. His first contribution had the merit of being quite original in conception and execution, for he then knew almost nothing of what others had done; he was entirely ignorant of the important paper of his fellow-countryman, Mayer, and knew only a little of Joule's earlier work. The principle of the conservation of energy, which for a quarter of a century has been the open sesame to every important advance in physical science, was not then, to say the least, a popular topic. But for five or six years a young Englishman named Joule, not yet 30 years old, had been engaged with it and, from the point of view of the engineer, had made it his own. On the 28th of April, 1847, he gave a popular lecture in Manchester, where he lived and died, which was the first full exposition of the theory. A few weeks later Helmholtz read his paper in Berlin. In England, even the local press refused to publish Joule's address, but finally the Manchester Courier, moved by the family influence (the elder Joule being a wealthy brewer), promised to insert the whole as a special favor. In Germany the subject met with only a little more favorable reception, and the leading scientific journal, Poggendorff's Annalen, declined to publish Helmholtz's paper. Even at the meeting of the British Association at Oxford a few months after the Manchester address, when Joule again undertook the exposition of his theory and his experimental proofs of it before what ought to have been a more friendly audience, he was advised by the chairman to be brief, and no discussion of his paper was invited. As Joule himself relates, his presentation of the subject would have again proved a failure "if a young man had not risen in the section and by his intelligent observations created a lively interest in the new theory." This young man was William Thomson, then 23 years old, now Lord Kelvin, the foremost of living physicists. The tremendous blows struck by Helmholtz in support of the new doctrine, from that time until it was no longer in the balance, give evidence alike of his extraordinary talents and his fine courage. The publication of this important essay in 1847 had also the effect of bringing about an immediate appreciation of his abilities. Du Bois-Reymond gave a copy of it to Tyndall, then a student of Magnus in Berlin, saying that it was the product of the first head in Europe. He was shortly removed to the more favorable environment of a university professorship at Königsburg. During the next twenty years he advanced from Königsburg to Bonn, from Bonn to Heidelberg and from Heidelberg to Berlin. While it was only on reaching the University of Berlin that he assumed his true function of professor of physics, yet the previous two decades had been rich in the application of physical methods to physiological subjects. In 1863 he published the remarkable monograph on the Sensations of Tone. This work is a most masterly analysis of the whole subject implied in its title and must always remain a classic. Only one or two of the most important results of the profound researches of the author can be referred to here. As everyone knows, the character of a musical tone is threefold. There is first its pitch, which has long been known to depend upon the frequency of vibration of the string or reed, or whatever gives rise to the sound; there is next the loudness, which depends upon the amplitude of this variation, or, in a general way, on the energy expended by the vibrating body. But two tones may agree in pitch and in loudness and still produce very different impressions on the ear. It is this which makes it possible to know when a musical tone is heard that it comes from an organ, or a flute, or the human voice. It enables an expert to know on hearing a single note from a violin that the instrument was made in a given year by a certain artist; by virtue of this characteristic one instantly recognizes a voice which one has not heard for many years as belonging to a particular individual. So little was known of the physical cause of this inherent peculiarity of a sound that for many years it went unnamed. Helmholtz called it the "Klangfarbe:" literally, "tone color;" but in English the term "quality" is now universally applied to it. What is the physical cause of the quality of a tone is the question the answer to which he sought. All that there is in a tone, he said-pitch, intensity, and quality-must be borne upon the air waves by which the sound is communicated to the ear, and all that these waves bear must be impressed upon them by the vibrating body in which the sound originates. He did not fail to recognize, however, and this was extremely important, that there might exist peculiarities in the receiving instrument, the ear (through the operation of whose mechanism the motion of matter is interpreted as a sensation), the existence of which would materially modify the final outcome, to the end that two physically identical tones might give rise, under certain circumstances, to different sensations. Guided by these principles, he discovered that the quality of a tone, that characteristic which gives charm to it, was really due to its impurity; that if two perfectly pure tones, generated by simple, pendular vibrations, agreed in pitch and loudness, it would be quite impossible to distinguish them. But practically, such tones are never produced; all ordinary tones are composite, made up of the fundamental, which generally fixes the nominal pitch of the whole, and a series, more or less complete and extended, of overtures or harmonics, the vibration frequencies of which are two, three, four or some other multiple of that of the fundamental. Without these, the fundamental, though pure, was plain, dull, and insipid; with them it formed a composite with quality, soft it may be, or brilliant, or rich, or harsh, or any of the thousand things which may be said of a tone. Which it was and what it was, was determined by the relative proportions of the several overtones, indefinite in number, in the composite whole. This beautiful hypothesis was illustrated and established by innumerable experiments, and it was proved that the form of the air wave was the quality of the tone, and that this form originated in the mode of vibration of the sounding body, which was almost universally not simple, but complex. But the most important work of Helmholtz along this line was the extension of this theory to the solution of a problem more than two thousand years old, proposed, in fact, by the Greek, Pythagoras. It meant nothing less than the physical explanation of harmony. Why are certain combinations of musical tones agreeable and others unpleasant? And, indeed, the answer to this tells as well why a certain succession of tones, as in a musical scale, is likely to be generally acceptable to the human ear. Lack of time will only permit me to say that in the interference and consequent beating of certain of the overtones or upper partials of two fundamentals, Helmholtz found the explanation of their dissonance, and that while in certain particulars his theory as originally published has been criticised, it is in general universally accepted and admitted to be one of the most splendid contributions to modern science. I am warned, also, that I must not speak of that other great work, the Physiological Optics, as I would so gladly do if time permitted. Helmholtz was actually engaged in the preparation of this and the Sensations of Tone during the same years. No other man in the world could have written these, for no other was at once an accomplished physiologist, mathematician, and physicist. While I can not speak of his contributions to the science of optics and ophthalmology, I must not omit brief reference to his invention of the ophthalmoscope and the ophthalmometer. Anxious to actually see what goes on in the eye, and especially on the retina, that wonderful screen on which the image of the visible world is focused, he invented the ophthalmoscope. The qualitative victory was followed by the quantitative in the invention of the ophthalmometer, by means of which accurate measurements of the various curved surfaces in the eye could be made. These two instruments have been to ophthalmic surgery what the telescope and graduated circle have been to astronomy. So exact has the science of the |