DIFFEREXritrrOX OF SOUNDS 265 



shorter. This may be shown clearly on a iiuxlel ear built to 

 demonstrate either Helmholt/Zs or Ewakrs tlieory. 



Timbre or (-liiality. Most sound-producing instruments impart 

 a characteristic quality to the sounds emitted by them. Anyone, 

 for instance, could tell whether a specific note were produced from 

 a piano, a violin, a pipe-organ, a harmonium, etc. This is due to 

 the fact that not only does the instrument vibrate as a whole, but 

 each individual part tends to vibrate in a characteristic way. 

 These partial viln-ations give rise to overtones, which impart 

 quality to the production in accordance with their number, their 

 pitch and their relative intensities. The ear, therefore, has no 

 need to develop a special mechanism for the purpose of appreciating 

 timbre. 



We must now consider the physical reasons for the peculiar 

 shape of the cochlea. Why should it take two and a half turns up to 

 the helicotrema, and why should it be a double body, e.g. scala 

 media sandwiched in betw^een the sccdae vestibuli and tiimpani? 

 If the cochlear tube w^ere straight, having at one end the oval 

 window with the stapes and at the other the round window with 

 its compensating membrane, the floor of the tube being the basilar 

 membrane with appendages, and the tube being practically of 

 uniform width throughout, w^e would ha\-e a receptor capable of 

 the maximum distortion possible, and also liable to have induced 

 in its fluid ripples and changes of pressure due to physical changes 

 other than sound waves. Every time that we started to move 

 our heads in space with or relatively to our bodies we would cause 

 a movement of the cochlear fluid and w^ould receive the sensation 

 of sound. The same thing would happen every time we changed 

 either our rate of movement or its direction. What a deafening 

 crash there would be when we violently applied negative accelera- 

 tion, e.g. express train stopping suddenly. This disadvantage 

 could be overcome partially by bending the tube into a U with 

 the two windows close together. A stricture at the bend of the U 

 would further help matters. We would now be able to move 

 linearly in any direction and alter our rate of progression without 

 hearing about it. An angular displacement would still disturb 

 hearing, especially if the movement were at all rapidly initiated or 

 stopped. The winding of the tube into a narrow spiral gives us 

 an organ of hearing containing a liquid that undergoes very little 

 relative displacement with the ordinary movements of the body. 

 It still tends to generate sounds when extraordinary motion or 

 acceleration is applied to the body. 



The double nature of the organ is a structural necessity. The 

 basilar membrane must vibrate in some fluid (gas or liquid) 



