THE DYNAMICAL THEOEY 

 OF SOUND 



INTRODUCTION 



1. Simple Vibrations and Pure Tones. 



In any ordinary phenomenon of sound we are concerned, 

 first with the vibrating body, e.g. a string or a tuning fork or 

 a column of air, in which the disturbance originates, secondly 

 with the transmission of the vibrations through the aerial 

 medium, next with the sensations which the impact of the 

 waves on the drum of the ear somehow and indirectly produces, 

 and finally with the interpretation which, guided mainly and 

 perhaps altogether by experience, we put upon these sensations. 

 It is in something like this natural order that the subject 

 will be discussed in the following pages, but the later stages 

 involving physiological and psychological questions can only be 

 touched upon very lightly. 



As few readers are likely to take up this book without 

 some previous knowledge of the subject we may briefly re- 

 capitulate a few points which will be more or less familiar, with 

 the view of fixing the meaning of some technical terms which 

 will be of constant occurrence. Many of the matters here 

 referred to will of course be dealt with more fully later. 



The frontier between physics and physiology is reached at 

 the tympanic membrane, and from the physical standpoint it is 

 to the variations of pressure in the external ear-cavity that we 

 must in the last resort look, under normal (as distinguished 

 from pathological) conditions, for the cause of whatever sensations 

 of sound we experience. These variations may conveniently 

 be imagined to be exhibited graphically, like the ordinary 

 variations of barometric pressure, by a curve in which the 

 abscissae represent times and the ordinates deviations of the 



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