506 STUDIES IN ADVANCED PHYSIOLOGY. 



having the strings of the other instruments set in sympa- 

 thetic vibration by the sound waves emanating from the 

 first. 



It must be noted, however, that one note will produce a 

 sympathetic vibration of another only when the two notes 

 so produced are of the same pitch, or bear at least harmonic 

 ratios to each other. To sing middle C into a piano will 

 set in vibration the string of middle C, not that of D or B. 

 To understand the nature of sympathetic vibrations thor- 

 oughly means to understand the manner in which the vibra- 

 tions of the air are finally transmitted to certain chords in 

 the ear. 



The ear has a piano-board in it and sounds entering it 

 will set in sympathetic vibration those chords which are 

 attuned to them. 



The physical explanation of these sympathetic vibrations 

 is simple. One can easily see how a very slight wind which 

 would come in regular puffs might set a very heavy object 

 swinging after a while if these puffs should occur at such 

 regularities that they would always strike the swinging 

 object just at the proper time. When the waves of air are 

 synchronous with the vibrations of the body a slight wave 

 may soon put in motion a relatively large body. If we 

 imagine an individual sitting in a swing and pushed with 

 but one finger, but the push administered just at the moment 

 when the person is swinging away from the finger, so as to 

 get the full benefit of the push, the swing may be soon set 

 in motion by these slight finger tips. 



So with the vibrations entering the ear and striking a 

 certain string whose vibrations are exactly attuned to it, 

 they finally set it going and so give rise to the production of 

 a second sound which is the counterpart of the first. 



Having in this preliminary way called attention to some 

 of the elementary but fundamental properties of sound, it 

 is possible to more intelligently understand the somewhat 

 complicated anatomy of the auditory apparatus itself. 



