IV 



THE DEVELOPMENT OF THE TELEPHONE 



FULLY to understand the action of the telephone 

 it should be recalled that all sounds are produced 

 by vibrations of matter, and that any sound to be 

 appreciated by the sense of hearing must be conveyed 

 to the sense organs of the ear by the repetition of sound 

 vibrations through some such medium as air, water, iron, 

 etc., air of course being the usual medium. Any body 

 from which sound proceeds, therefore, is in a state of 

 vibration. This may be demonstrated by the simple 

 experiment of striking a thin glass jar, causing it to 

 vibrate and produce sound, the vibratory motion being 

 distinctly felt if the jar is touched lightly when the sound 

 is loudest, and gradually ceasing as the sound dimin- 

 ishes. The same vibrations and sounds may be pro- 

 duced by drawing a violin bow across the top of the 

 jar; and if little balls of wood are suspended by several 

 inches of string so that they just touch the sides of the 

 jar near the top, these will be thrown into a state of 

 vibration, oscillating back and forth against the jar as 

 the violin bow is drawn across it. In this way the 

 sound vibrations are made evident to sight as well as 

 hearing. 



In this experiment the air acts as the vibrating me- 

 dium for conveying the sound waves from the glass jar 



[66] 



