QUALITY OF MUSICAL SOUNDS. 181 



Another element in the quality of tones depends upon 

 their reinforcement by resonance. The vibrations of a 

 stretched string, not connected with a resonant body, are al- 

 most inaudible. 1 In musical instruments, we have the tone 

 taken up by some mechanical arrangement, as the sound- 

 board of the organ, piano, violin, harp, guitar, etc. In the 

 violin, for example, the sweetness of the tone depends chiefly 

 upon the construction of the resonant part of the instrument, 

 and but little upon the strings themselves, which are fre- 

 quently changed. The same is true of the human voice, of 

 wind-instruments, etc. We could not discuss these points 

 elaborately, without giving a full description of the various 

 musical instruments in common use, which would be out of 

 place in a work on physiology. 



In addition to the harmonic tones of sonorous bodies, 

 various discordant sounds are generally present, which modify 



1 The reenforcement of sounds by resonance is beautifully illustrated by an 

 experiment originally made by Wheatstone, which is very graphically described 

 by Tyndall, in his lectures on sound. (TYNDALL, Sound, London, 1867, p. 80.) 



" We are now prepared to appreciate an extremely 'beautiful experiment, for 

 which we are indebted to Prof. Wheatstone, and which I am now able to make 

 before you. In a room underneath this, and separated from it by two floors, is 

 a piano. Through the two floors passes a tin tube 2 inches in diameter, and 

 along the axis of this tube passes a rod of deal, the end of which emerges from 

 the floor in front of the lecture-table. The rod is clasped by India-rubber 

 bands, which entirely close the tin tube. The lower end of the rod rests on the 

 sound-board of the piano, its upper end being exposed ftefore you. An artist is 

 at this moment engaged at the instrument, but you hear no sound. I place this 

 violin upon the end of the rod ; the violin becomes instantly musical, not how- 

 ever with the vibrations of its own strings, but with those of the piano. I re- 

 move the violin, the sound ceases; I put in its place a guitar, and the music 

 revives. For the violin and guitar I substitute this plain wooden tray ; it is also 

 rendered musical. Here, finally, is a harp, against the sound-board of which I 

 cause the end of the deal rod to press ; every note of the piano is reproduced 

 before you. I lift the harp so as to break its connection with the piano, the 

 sound vanishes ; but the moment I cause the sound-board to press upon the rod, 

 the music is restored. The sound of the piano so far resembles that of the harp 

 that it is hard to resist the impression that the music you hear is that of the 

 latter instrument. An uneducated person might well believe that witchcraft is 

 concerned in the production of this music." 



