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[N. S. Vol. III. No. 58. 



the section and by his intelligent observa- 

 tions created a lively interest in the new 

 ■theory.' This young man was William 

 Thomson, then twenty- three years old; 

 now,' Lord Kelvin, the foremost of living 

 physicists. 



The tremendous blows struck by Helm- 

 holtz in support of the new doctrine, from 

 that time until it was no longer in the 

 balance give evidence alike of his extraor- 

 dinary talents and his fine courage. The 

 publication of this important essay in 1847 

 had also the effect of bringing about an im- 

 mediate 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 Konigsburg. During the 

 next twenty years he advanced from. Konigs- 

 burg 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 Pro- 

 fessor of Physics, yet the previous two de- 

 cades had been rich in the application of 

 physical methods to physiological subjects. 



In 1863 He pubUshed 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 every one 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 vir- 

 tue 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 un- 

 named. Helmholtz called it the ' Klang- 

 farbe ' literally, ' tone-color ; ' but in Eng- 

 lish 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 origir 

 nates. He did not fail to recognize, how- 

 ever, and this was extremely important, 

 that there might exist pecuHarities 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 phy- 

 sically identical tones might give rise, un- 

 der certain circumstances, to different sen- 

 sations. 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 per- 

 fectly 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 



