790 * HELMHOLTZ. 



doctrine, from that time until it was no longer iri the balance, give evi- 

 dence alike of his extraordinary talents and his fine courage. The 

 publication of this important essay in 1847 had also the effect of bring- 

 ing about an immediate appreciation of his abilities. Du Bois-Reymond 

 gave a copy of it to Tyndall, then a student of Magnus in Berlin, say- 

 ing that it was the product of the first head in Europe. He was shortly 

 removed to the more favorable environment of a university professor- 

 ship at Koiiigsburg. During the next twenty years he advanced from 

 Konigsburg 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 musi- 

 cal 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 artfst; 

 by virtue of this characteristic one instantly recognizes a voice which 

 one has not heard for many years as belonging to a particular indi- 

 vidual. 



So little was known of the physical cause of this inherent peculiarity 

 of a sound that lor many years it went unnamed. Helmholtz called it 

 the "Klangfarbe;" literally, "tone color;' 7 but in English the term 

 lt 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 



