THE EAK 3/1 



much as do the various wires of a piano. When, therefore, 

 the liquids in the inner ear are thrown into vibration, it is 

 evident that some part of the organ of Corti will naturally 

 vibrate with exactly the same rapidity as the movements of 

 the liquid, according to the laws of sympathetic vibration. 

 Thus for every different sound a nerve fibre will be stimulated, 

 and the brain recognizes the different pitches. While this 

 general theory of tone perception seems to be reasonable and 

 correct, we must admit that as yet no one knows precisely 

 what part the organ of Corti plays in the appreciation of 

 sounds. 



Loudness of Sound. Loudness of sound depends, not on 

 the rate at which air is moving in waves, but on the size of 

 the waves; not on the rapidity of vibrations, but on their 

 amount. This we know from the simple fact that a piano 

 string struck heavily will give out a loud sound; if struck 

 gently, a low sound, though of the same pitch as when struck 

 heavily. Violent movements in the air are set up when the 

 string is vibrating back and forth through considerable dis- 

 tance after being struck hard, and these start large waves 

 in the surrounding air, which however vibrate at the same 

 rate as if the wire had been struck gently. These violent 

 movements are finally transferred to the inner ear over paths 

 we have already discussed, and thus the nerve endings in the 

 organ of Corti are greatly irritated. One interprets this 

 strong stimulation as loudness of sound; faint sounds are con- 

 versely due to very slight air waves and slight nerve stimula- 

 tion. 



When listening intently to catch some faint sound, almost 

 everyone strikes the same instinctive attitude. The body is 

 held very quietly, the ear turned in the direction from which 

 the sound is expected, and the whole attention is focused on 

 the ear. In the perception of faint sounds, slight changes 

 occur in the middle ear, and the purpose of these changes may 

 be understood from the analogous action of a drumhead. 



