192 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



required to bring about this result, we can readily calculate 

 the number of vibrations per second of the solid. Professor 

 Rood has given the results of this method in determinations 

 of the vibrations of cords, rods, bars, plates, bells, and mem- 

 branes, and finds that he can determine to from one to two 

 tenths of a vibration the number of vibrations per second of 

 these bodies. 



ON THE MODE OF HEARING IN MAN AND MAMMALS. 



Professor Alfred M. Mayer, from calculations on the effects 

 of the form of the cochlea of the inner ear on the sonorous 

 vibrations which enter it, arrived at the conclusion that the 

 terminal fibrils of the auditory nerve vibrate, in a given time, 

 only half as frequently as the membrane of the drum of the 

 ear. The auditory nerve fibrils are attached to the middle 

 points of about 18,000 minute elastic rods or cords, stretched 

 between the basilar membrane of the ductus of the cochlea 

 and what is known as the lamina reticularis. Professor Mayer 

 is of the opinion that these cords and their attached nerve 

 fibrils do not receive their vibrations from sonorous pulses 

 sent directly into the ductus, but are set in vibration by tre- 

 mors imparted to them from the basilar membrane. The bas- 

 ilar membrane itself is vibrated by the pulses sent into the 

 ductus from the membrane of the drum of the ear, through 

 the intervention of the chain of minute ear-bones. Hence 

 any one of these stretched cords must vibrate half as often 

 in a second as does the basilar membrane, or the membrane 

 of the tympanum. Now it is a fact easily proved experi- 

 mentally that a stretched cord, attached to a vibrating mem- 

 brane, must make, in the same time, half as many vibrations 

 as the membrane. 



Professor Mayer has illustrated his view of the manner 

 in which we hear by the following experiment : A loosely 

 stretched membrane, placed near a sounding reed-pipe, stands 

 for the basilar membrane ; stretched strings of various lengths 

 and diameters, and loaded at their centres, are attached to 

 the membrane, and stand for the minute tuned cords of the 

 ductus. On sounding the reed-pipe, only those strings in 

 tune with the harmonics existing in the composite sound of 

 the reed will enter into vibration; similarly, when the same 

 sound-vibrations enter the inner car, and vibrate the bas- 



