610 MANUAL OF PHYSIOLOGY. 



only the string which sounds the note vibrates, but also all those 

 strings that have a certain simple numerical relation to its number 

 of vibrations. In fact, all its over-tones or harmonics are also 

 sounded. Now, in the cochlea we suppose the same takes place 

 with the fibres of the basilar membrane. Not only does the one 

 fibre whose proper tone is sounded vibrate in response, but also 

 all those fibres which represent the many and varied over-tones 

 or harmonics of the fundamental tone that reach the ear. It has 

 already been pointed out that quality of a note depends on the 

 relative number, force, and arrangement of the harmonics which 

 invariably accompany any musical note possessing a definite 

 character. 



When such a note, then, arrives at the auditory nerve termi- 

 nals, one of these is strongly stimulated by the wave of the fun- 

 damental tone, and many others are stimulated by the different 

 over-tones. Thus, a complexity of impulses, corresponding to a 

 mixture of tones of varying intricacy, is transmitted to the brain 

 cells, where it gives rise to the impression of the quality which 

 we by experience associate with that of a violin, flute or piano, 

 as the case may be. 



With regard to the judgment of the distance of sounds, it need 

 only be remarked that they chiefly depend on former experience 

 of the habitual quality and intensity of the sounds. A faint 

 sound with the same quality that we familiarly attribute to loud 

 sounds seems to us to be far away. Thus, sounds reaching our 

 labyrinths by the cranial bones appear distant, and ventriloquists 

 deceive us by imitating the character of distant sounds. 



In man the direction from which sounds come is chiefly judged 

 by the difference of distinctness with which they are heard by 

 one or other ear. When we cannot form any idea of whence a 

 sound comes, we usually turn our heads one way or the other, in 

 order to present one ear more directly to the origin of the sound. 

 When a sound is either directly behind or before us we cannot 

 judge which position it really comes from, unless the head be 

 slightly turned to one side or to the other. 



