MECHANISM OF HEARING. IQI 



sounds which are easily perceived and appreciated by the 

 ear vary from 100 to 2000 vibrations. The gravest C of 

 a piano of six octaves and a half counts 128, and the most 

 acute 8192. 



Mechanism of hearing. The sonorous waves penetrate 

 directly into the auditory canal, or after they have en- 

 countered the outer portion of the ear, the sinuosities of 

 which they follow, and the ear itself vibrates to the shock of 

 sounds, and these vibrations are transmitted gradually to the 

 organ. Savart, who has demonstrated this phenomenon by 

 experiments, observes that the very irregular surface of the 

 ear always presents some portion at an angle most favourable 

 to the sonorous waves, whatever may be their direction ; in 

 fact, the force with which they act upon its walls is in direct 

 proportion to their approach to the perpendicular. 



If, for example, the pavilion of the right ear be covered 

 with some substance which obliterates all the inequalities 

 and transforms it into a plane surface, a sound cannot be 

 heard on that side so well as on the left, when produced at 

 an equal distance from both ears. It is to be presumed, 

 also, that the pavilion, which increases all sounds equally, 

 does not vibrate in unison with any one sound, nor has it, 

 owing to the irregularities of its surface, any one peculiar to 

 itself. And finally, the form of the pavilion, and its inclina- 

 tion in relation to the head, seem to have a certain influence 

 on the acuteness of hearing. 



Besides the vibrations which enter directly into the audi- 

 tory canal, and those which come from the pavilion, this 

 canal receives also those of the bones of the cranium and 

 transmits them to the tympanum. These last and those of 

 the pavilion reach the tympanum sooner than the first, for 

 the reason already stated, that sounds move more rapidly in 

 fluids and solids than in the atmosphere. It receives there- 

 fore two orders of vibrations, but in passing to this membrane 

 the vibrations of the air are transformed into those of a solid 

 body; from which we may conclude with Savart and Miiller, 

 that the function of the tympanum is to serve as a medium 

 between the air and the small bones of the ear, by changing, 

 as we have just seen, the atmospheric vibrations. 





