PROPERTIES OF SOUND 599 



THE ORGAN OF HEARING 



From a knowledge of the fundamental properties of sound it is possible 

 to infer the probable features of the organ of hearing. In its simplest variety 

 the organ would take the form of a sounding board or diaphragm which would 

 be set into vibration by the incident sound waves. The vibrations of this 

 plate would be identified by touch cells similar to those found in he skin, 

 which would be so placed that the diaphragm during its motion should come 

 into contact with them. Such an apparatus would respond to and estimate 

 the total intensity of sound. To identify the pitch a series of resonators 

 would be required, each of which would be sharply tuned to one of a series 

 of tones. Of the many types of resonator that could be employed a series 

 of stretched wires would appear to be the simplest and most compact. The 

 receiving apparatus would therefore take the form of a harp with a touch 

 cell and its respective nerve attached in close approximation to every 

 chord. 



In order that such a mechanism may be formed of organic material 

 and be kept nourished during life, it is necessary that it be immersed in a 

 liquid similar to that which bathes the eye media. The sound waves must 

 therefore be transmitted from the air to this fluid. In order that this may 

 occur it is necessary that the sound waves reach the apparatus either (1) 

 through the walls of the chamber containing the apparatus, i.e. bone conduc- 

 tion, or (2) through a membrane separating the liquid from the air, or (3) 

 by means of suitable levers which would impart to the liquid the vibration 

 of an external diaphragm. The advantage of the latter method would 

 be that the intensity of sound reaching the apparatus could be considerably 

 increased. This desirable result could be still further achieved by concen- 

 trating the sound waves on to the diaphragm by means of a trumpet and by 

 causing the trumpet to be adjustable in different directions. The position 

 of the source of sound could then be ascertained. 



Such an organ of hearing would therefore consist of three different parts : 



(1) the horn or trumpet with its adjusting muscles, called the external ear ; 



(2) the diaphragm and levers for receiving the sound vibrations and for 

 transmitting them to the internal mechanism, called the middle ear ; and (3) 

 the internal mechanism consisting of the resonators with their respective 

 touch cells and nerves called the internal ear. 



