554? HEARING. 



however, supposed that it was stretched for intense impressions, 

 and relaxed for the weaker, which is contrary to what is de- 

 monstrated by experiment. 3dly. That its vibrations are com- 

 municated without alteration to the labyrinth by means of the 

 chain of small bones, in the same manner as the vibrations of the 

 belly of a violin are communicated to the back by means of the 

 sound post. 4thly. That the small bones have also for their func- 

 tion to modify the amplitude of the excursions of the vibrating 

 parts of the organs contained within the labyrinth. And lastly, 

 That the cavity of the tympanum probably serves to maintain, 

 near the openings of the labyrinth and the internal surface of 

 the membrana tympani, an air the physical properties of which 

 are constant. 



Weber has endeavoured to explain the use of the cochlea. 

 He remarks that sound is propagated through, not only the meatus 

 auditorius externus, but the bones of the head ; and, indeed, more 

 distinctly through them. If both ears are stopped firmly with the 

 fingers, our own voice becomes more loud and distinct. If we re- 

 move one finger immediately, we hear our own voice stronger with 

 the other ear. If a musical sounding fork under vibration is placed 

 between the teeth, the lips closed and both ears stopped, its 

 tones are heard louder than if the ears were open : open one 

 ear, and the sound is lessened to that ear. If the fork is applied 

 to the left temple and the right ear only closed, the sound is 

 louder to the right ear than to the left which is open. Now 

 sounds propagated through one uniform medium, fluid or solid, 

 lose but little of their force ; whereas in passing from one medium 

 to another, as from a fluid to a solid or vice versa, they lose much 

 of their force. In the shaft of a mine the sound of a hammer in 

 a neighbouring shaft is heard very well if the ear is placed in con- 

 tact with the rock ; if this is not done it is heard less, and the 

 sound of voices in the other shaft not at all. Sounds transmitted 

 through water may be heard at great distances if the head is under 

 water ; and are inaudible as soon as the head emerges. The effect 

 of a window in lessening the noises of the street is a similar instance 

 Now the sonorous vibrations which pass from the air through the 

 bones of the head to the internal ear will act on the cochlea, be- 

 cause it is the nearest and has its share of the acoustic nerve in 

 intimate contact with itself, and is both osseous and forms a portion 

 of the osseous communication between the mouth and the internal 



