TONES BY INFLUENCE 



733 



The laws just stated are applicable to overtones, resultant tones and 

 additional tones, which, like the primary notes, have their beats and 

 discords. 



Tones by Influence. After what has been stated in regard to the 

 laws of musical vibrations, it will be easy to comprehend the production 

 of sounds by influence. If a key of the piano is lightly touched so as 

 to raise the damper but not to sound the string, and then a note is 

 sung in unison, the string will return the sound, by the "influence" of 

 the sound-waves of the voice. The sound thus produced by the string 

 will have its fundamental tone and overtones ; but the series of over- 

 tones will be complete ; for none of the nodes are abolished, as in 

 striking or plucking a string at any particular point. If, instead of a 

 note in unison, any of the octaves are sounded, the string will return 

 the exact note sung ; and the same is true of the 3d, 5th etc. If a 

 chord in harmony with the undamped string is struck, this chord will 

 be exactly returned by influence. In other words, a string may be 

 made to sound by influence, its fundamental tone, its harmonics and 

 harmonious combinations. To carry the observation still farther, the 

 string will return, not only a note of its exact pitch and its harmonics, 

 but notes of the peculiar quality of the primary note. This is an im- 

 portant point in its applications to the physiology of hearing and can be 

 readily illustrated. Taking identical notes in succession, produced by 

 the voice, trumpet, violin, clarinet or any other musical instrument, it 

 can easily be noted that the quality of the sound, as well as the pitch, is 

 rendered by a resounding string ; and the same is true of combinations 

 of notes. The laws of tones by influence have been illustrated by 

 strings merely for the sake of simplicity ; but they are applicable more 

 or less to all bodies capable of producing musical sounds, except that 

 some are thrown into vibration with more difficulty than others. 



A thin membrane, like a piece of bladder or thin rubber, stretched 

 over a circular orifice, such as the mouth of a wide bottle, may readily 

 be tuned to a certain note. When arranged in this way, the membrane 

 can be made to sound its fundamental tone by influence. In addition, 

 the membrane, like a string, will divide itself so as to sound the har- 

 monics of the fundamental, and it will likewise be thrown into vibration 

 by the 5th, 3d etc., of its fundamental, thus obeying the laws of vibra- 

 tions of strings, although the harmonic sounds are produced with greater 

 difficulty. 1 



1 The account just given of some of the laws of sonorous vibrations and their relations to 

 musical effects and combinations, although by no means complete, may seem rather extended 

 for a work on physiology; but it should be borne in mind that the mechanism of the apprecia- 

 tion of musical sounds includes the entire physiology of audition. This subject can not be 



