Popular Science Monthly/Volume 37/August 1890/Sketch of Rudolph Koenig

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IN examining the personal records of men who have contributed to the advancement of human knowledge, one of the features most frequently noticed is the necessity to meet adversity in early life. Perhaps it is but little less frequently the case that they are compelled throughout life to content themselves with a minimum of pecuniary reward for the mental work which meets due appreciation only after its final close. The thirst for discovery, the craving after truth, apart from all considerations of emolument, exist germinally in every young human being; but the rewards that the world gives for brain-work, other than what is directed toward the discovery of truth, are sufficient to determine most men and keep them occupied in fields other than scientific. Native bent, if fortified with force of character, finds its channel in time, whatever may be the accidents of childhood; and uncongenial occupation has been the lot of many who have used it as the basis of future renown.

Quite a number of those who have achieved distinction in physical science have, in early life, or throughout life, given a considerable share of attention to the mechanical details involved in constructing the instruments needed for investigation. Newton began in youth the making of machines, and his skill as a practical optician was only less remarkable than his genius as a mathematician. Herschel practiced music as a profession, while giving all his spare time to the grinding of telescope mirrors and to observational astronomy. Ruhmkorff wandered to Paris as a boy of sixteen, and became a porter in the laboratory of a French physicist. In time his name became known wherever the induction coil is used, whether in the investigations of the physicist or in the operations of commercial electricity. Wheatstone adopted the vocation of a maker of musical instruments in preference to grinding Greek and Latin verses at school. This work he continued for many years, achieving world-wide distinction as an original investigator in acoustics, and afterward in optics and electricity.

Younger than Ruhmkorff and Wheatstone, but amply worthy of being classed with them, is Rudolph Koenig, the most distinguished living inventor and mechanician in the domain of acoustics. He was born on the 26th of November, 1832, in Koenigsberg, Prussia. His father was teacher of mathematics and physics in the city gymnasium, where the son as pupil received the usual high-school training, corresponding in some particulars to the academic work in most American colleges. He exhibited much aptitude in physics as well as music; but, being compelled to depend upon his own resources, he went to Paris at the age of nineteen years, to devote himself to the construction of stringed instruments. Here he worked for several years under the direction of the celebrated violin-maker Vuillaume, but at the same time devoted such leisure as he could command to the study of mechanics and physics.

Quite naturally acoustics was the branch of physics which presented most attraction to the young mechanician, and in time it claimed his almost undivided allegiance. Meanwhile his success was such as to warrant him in undertaking business on his own account, so that in 1858 he fitted up a working place for the construction of acoustic apparatus, and in 1859 he issued his first catalogue, containing descriptions and illustrations of the various instruments made by him. Some of these were improvements upon instruments already in use, but many were new, the outcome of Koenig's own ingenuity. This catalogue formed the basis of the subsequent expansions which appeared in 1865, 1873, 1882, and 1889. The last is a volume of one hundred pages, with descriptions of two hundred and seventy-two instruments, in French, English/and German, and including probably everything that is employed in modern acoustic investigation.

It was in 1862 that Koenig began to be known to the scientific world as an investigator. An International Exhibition was held during that year in London, and the indefatigable instrumentmaker was present, not merely for the purpose of displaying the products of his labor, but to use these in the presence of physicists and to show practically the value of the graphic method of studying harmonic motion which had grown almost to perfection in his hands. The mathematical analysis of wave-motion had been abundantly brought out in technical treatises. Dr. Thomas Young, in the beginning of the present century, had pointed out the method by which a tuning-fork might be made to trace a record of its own vibrations, and his hint was put into practice nearly half a century afterward by Wertheim and Duhamel. But Koenig was the first to apply this method systematically to the registration of not only simple vibrations but also compound harmonic motion; and a large variety of such phonograms executed with apparatus of his device, and accompanied with the tracings of the corresponding theoretical curves, attracted much attention at the exhibition. The method has since been adopted in a number of other fields, notably in physiology for the analysis of animal motion, and in general physics for the measurement of minute intervals of time.

At the same exhibition in 1862 Koenig exhibited a wholly new method of making the effects of sonorous vibration easily visible by utilizing the delicate sensitiveness of flame to variations of atmospheric pressure. Four years earlier some noteworthy experiments had been made in America by Le Conte on the effect of such vibrations upon naked gas-flames; but no development had thus far been evolved from them. Koenig devised the manometric capsule through the medium of which the pressure at the outflowing jet is modified at will by sound-waves conducted to an elastic membrane. The motion of this produces pulsations in the gaseous fuel, and their effect on the flame is observed by looking at its image reflected from a revolving mirror. This beautiful method has been applied by its originator with much success to the study of the interference of sound, and to the investigation of the quality of musical sounds. No two vowels can be sung in succession to the delicate flame without impressing on it their separate individuality; and the eye is thus permitted to compare differences which the ear may recognize but not analyze. To see one's own voice in a mirror, to watch the successive phases of melody and harmony, to see two sounds interfering and producing visible silence—these are some of the revelations of the manometric flame.

This remarkable exhibition of Koenig's originality brought him prominently into notice everywhere. A detailed description of his work was published soon afterward by Prof. Tisko in Vienna, and from that day to this he has had no rival in the field which he had made his own. In every university where acoustics is taught Koenig's apparatus is the standard. Honors also were soon accorded in acknowledgment of his merit. Among these may be mentioned a gold medal, in I860, from the Sociéte d'Encouragement at Paris; a gold medal, in 1867, from the International Exhibition at Paris; in 1868 the honorary degree of Doctor of Philosophy, from the university of his native city, Koenigsberg; and, in 1876, a medal from the Centennial Exhibition at Philadelphia. Before scientific assemblies he has been called upon to give the results of his investigations, including in them the Assembly of German Naturalists, in 1868, at Dresden; the American Association for the Advancement of Science in 1876 at Buffalo, and again in 1882 at Montreal; and the Electrical Exhibition at Paris in 1881, when he was specially visited by a large company of the most renowned of living physicists, including Helmholtz, Kirchhoff, Du Bois-Reymond, Clausius, Quincke, Mach, Kundt, Pahlzon, and Sir William Thomson.

The scientific papers of M. Koenig have been published almost entirely in the Annalen of Poggendorff and of Wiedemann. Most of these have been translated into French and published, in 1882, in a volume entitled Quelques Expériences d'Acoustique. To give an adequate idea of what is included in them would be impossible without going into detail. The volume includes a full account of Koenig's application of the graphic method and that of manometric flames. Both these methods are applied in an exhaustive investigation of the beat tones which result from the combination of two or more primary tones. Helmholtz discussed "differential tones" and "summation tones," whose existence was inferred from the results of mathematical analysis; and certain phenomena seemed for a time to confirm the conclusions of the great German physicist. But Koenig subsequently applied the most patient care and consummate skill in the experimental examination of these phenomena. Without detracting at-all from the credit due Helmholtz for his splendid researches, it may now be safely said that Koenig's experiments have shown that differential and summation tones are due exclusively to the beats which the ear perceives when impressed simultaneously by systems of waves differing in length. The effect is physiological, and such combination tones are not at all re-enforced by resonators like the separate primaries that enter into combination. It is not necessary that beating tones shall be nearly in unison, as is stated in so many of the text-books.

The subject of musical quality was long an unsolved enigma for physicists. The principle underlying its explanation was foreshadowed early in the present century by the French mathematician Fourier, and soon afterward applied to acoustics by Ohm, whose name is now so familiar in connection with electricity. But to Helmholtz is due the full experimental proof that the quality of every musical sound is determined by the number, orders, and relative intensities of the upper partial tones which accompany the fundamental whenever any ordinary instrument is sounded. Every such compound tone can be graphically represented by its own curve, the form of which may be varied not only by varying the elements just mentioned, but also by varying the phases in which the separate components are joined together. Helmholtz endeavored to test the influence of change of phase in using his apparatus for acoustic analysis, but the results were negative, and his conclusion was, that variation in phase has no physiological effect. Koenig has since attacked this problem, employing wave-sirens of his own invention, by which he has established quite conclusively the existence of this fourth element of musical quality. . . . The wave-siren may be briefly described as an apparatus in which a blast of air is forced through a narrow cleft against the edge of a moving plate or disk on which a series of determinate wave-forms have been cut. Each sinuosity, as it passes the cleft, interrupts the egress of air, so that a series of compound pulses are propagated whose grouping is determined by the form of the curved edge. The pitch is determined by the speed of rotation and the wave-length cut in the metal, through either the convex surface of a cylinder which rotates on its axis, or the edge of a disk which rotates about its center. A number of such wave-forms, each with its own wind-cleft, may be operated at the same time, with the same speed and with the same pressure of air at each cleft. They may be arranged to either coincide or differ in phase to any required extent. By the use of this new instrument Koenig has found that the complex sound obtained by the composition of a series of harmonics, of even as well as odd orders, quite independently of their relative intensity, has always its maximum of strength and its greatest acuteness of quality for a difference of phase of a fourth of a wave-length; the minimum of strength, and the softest quality, for a difference of phase of three fourths of a wave-length. It may be said that, if changes in the number and relative intensity of the harmonics produce differences of quality, such as are observed in instruments belonging to different families, or such as the human voice shows in the different vowels, the changes due to difference of phase between the same harmonics are yet capable of producing differences of quality at least as sensible as those which are noticeable in instruments of the same kind, or in the same vowels sung by different voices.

All musicians are able to perceive the general smoothness or roughness of a combination of sounds; but the analysis of the combination requires exquisite sensitiveness of ear for the detection of variation in both pitch and harmony. In the tuning of the standard forks which are issued from Koenig's laboratory, his ear is usually found to be a sufficient guide, and at standard temperature these are rarely if ever found to deviate by more than a fraction of a single vibration from the value stamped upon them.

Within the last year Koenig has published two important papers: the one on beat tones due to the excitement of two separate motions of vibration on the same body; the other on tones due to the composition of waves of unlike form. These papers have an important bearing on the theory of musical quality. Their author is not yet sixty years old, and it is reasonable to expect from him many more contributions to the science of acoustics before old age interferes with the acuteness of his wonderfully accurate musical ear, or diminishes his power to do good work.

The following is a list of the principal contributions of M. Koenig to science, with their dates and the names of the periodicals in which they first appeared. The titles are translated into English, and the length of each article is approximately indicated by the number of pages covered:

1. On the Application of the Graphic Method to Acoustics. (Cosmos, 1862, pp. 27.)
2. Apparatus for the Measurement of the Velocity of Sounds at Small Distances. (Comptes Rendus de l'Académie des Sciences, October 13, 1862, pp. 2.)
3. Experiments relating to Wheatstone's Explanation of Chladni's Figures. (Comptes Rendus, March 27, 1864, pp. 7.)
4. A New Stethoscope. (Poggendorff's Annalen, 1864, pp. 2.)
5. Experiments to determine the Influence of the Movement of a Source of Sound on Pitch. (Koenig's Illustrated Catalogue, 1865, p. 1.)
6. On the Fixed Notes characteristic of Vowel Sounds. (Comptes Rendus, April 25, 1870, pp. 5.)
7. Manometric Flames. (Poggendorff's Annalen, 1872, pp. 36.)
8. A Tuning-Fork of Variable Pitch. (Poggendorff's Annalen, 1876, pp. 2.)
9. On the Phenomena produced by the Concurrence of Two Sounds. (Poggendorff's Annalen, 1876, pp. 62.)
10. On the Origin of Beats, and the Beating Sounds of Harmonic Intervals. (Wiedemann's Annalen, 1881, pp. 14.)
11. Description of an Apparatus for Lecture Demonstration of Beating Sounds. (Wiedemann's Annalen, 1881, pp. 4.)
12. Researches on the Difference of Phase existing between the Vibrations of Two Associated Telephones. (Journal de Physique, May, 1879, pp. 5.)
13. Researches on the Vibrations of a Normal Fork. (Wiedemann's Annalen, 1880, pp. 21.)
14. Harmonic Vibrations excited by the Vibrations of a Fundamental Sound. (Wiedemann's Annalen, 1880, pp. 13.)
15. A Method for observing the Air Vibrations in Organ-Pipes. (Wiedemann's Annalen, 1881, pp. 12.)
16. Remarks on Musical Quality. (Wiedemann's Annalen, 1881, pp. 26.)
17. On Beats and the Beat Tones of Two Vibratory Motions excited in the Same Body. (Wiedemann's Annalen, 1890, pp. 8.)
18. On Composite Tones, with Waves of Unlike Form. (Wiedemann's Annalen, 1890, pp. 9.)