THE TELEPHONE - . 495 



strung with telegraph wires and the ocean girdled with 

 cables, and now an important event occurring in any part 

 of the earth is known almost instantly in all other parts. 

 The telephone, the wireless telegraph, and the wireless 

 telephone, all electrical devices, have added to the ease of 

 communication so that the whole earth is brought into such 

 close relation that every part knows what all the other parts 

 are doing. 



The Greatest Electrical Discovery. In 1831, Michael 

 Faraday, an English physicist, made a discovery the results 

 of which have almost revolu- 

 tionized civilized man's in- 

 dustrial life. He found that 

 when a magnet is quickly 

 thrust into a coil of wire a FlGURE 167 



momentary electrical current is generated in the wire, and 

 when the magnet is removed a momentary current is gener- 

 ated in the opposite direction. The same effect is produced 

 if the strength of the magnet in the coil is quickly increased 

 or decreased, or if the coil is revolved between the poles 

 of a magnet. This discovery makes it possible to transform 

 mechanical energy into electrical energy and is responsible 

 for the invention of the dynamo, the motor, and many 

 other electrical devices. 



The Telephone. In 1875 Alexander Graham Bell first 

 communicated by telephone from Boston to Cambridge, a 

 distance of only a few miles. To-day man can talk across 

 the continent. Probably no device has resulted in greater 

 saving of time. 



The simple telephone (Figure 168) consists of a hard- 

 rubber case in which is a permanent bar magnet surrounded 



