DEVELOPMENT OF THE TELEPHONE 



to the ear; for if the jar were not surrounded by some 

 medium capable of transmitting similar vibrations, no 

 sound could be heard: If, for example, the jar were in a 

 vacuum, the sound of its vibration would not be con- 

 veyed to the ear. This was demonstrated by the strik- 

 ing experiment made by Francis Hauksbee in 1705. 



In this experiment Hauksbee placed a bell rung by 

 clockwork in the receiver of an air-pump. So long as the 

 air was not exhausted from the receiver the ringing of 

 the bell was heard distinctly, but as the air became ex- 

 hausted the sound of the ringing gradually diminished 

 until it entirely disappeared when the vacuum had been 

 produced, although the vibrations of the striker could 

 still be seen. In this condition the sound could be again 

 distinctly heard by allowing a little air to enter the 

 receiver, or by bringing a wire into contact with the bell, 

 the sound waves being conveyed along the wire to the 

 air outside, which then acted as a medium for their 

 transmission. 



The appreciation of sounds by the sense of hearing 

 is a function of the brain, and like all such functions 

 can only be vaguely understood. The mechanical ar- 

 rangement of the ear for receiving impressions of the 

 sound waves, however, is comparatively simple, being 

 the same as the mechanical apparatus made artificially 

 to interpret sound vibration. A thin membrane, like 

 a miniature drum-head, receives these vibrations just as 

 in the case of the membrane or diaphragm used in the 

 telephone receiver, and transfers them to the proper 

 "center" in the brain, where they are interpreted by 

 the sense of hearing. That this drum-head or diaphragm 



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