268 



GENERAL SCIENCE 



186. The Telephone. -- The telephone was invented 

 by Alexander Graham Bell, of Washington, in 1875. 



It has been in extensive 

 commercial use only 

 about 25 years. It was 

 at first a luxury, but has 

 become a necessity in 

 modern business. Tele- 

 phone lines are found 

 along nearly every public 

 highway. The telephone, 

 however, does not trans- 

 mit sound. The sound 

 waves that are made 

 when one speaks into 



Scientist and inventor, born March 3, the mouthpiece of a tele- 



1847, educated in Edinburgh and London, phone control the elec- 

 invented the telephone 1875. H C a l so . 



invented the photophone, induction bal- trie current which passes 



ance, telephone probe for painless detec- Qver the te l ep hone wire 



(C) Underwood and Underwood 



ALEXANDER GRAHAM BELL 



tion of bullets in the human body, and 

 assisted in the invention of the grapho- 

 phone. 



and into the receiver at 

 the other end. The 

 current going into the receiver causes an elastic piece of 

 sheet steel to vibrate with the same speed and quality 

 as the voice of the speaker which made the elastic sheet 

 steel in the mouthpiece vibrate. When the sheet steel in 

 the receiver vibrates it causes the air between it and the 

 ear-drum to vibrate and thus the sound is carried to the 

 ear. 



The modern telephone uses an induced current that 

 passes over the wire, rather than the current direct from 

 the battery. Hence a transformer, a form of induction 

 coil, is necessary to make the induced current. The 

 coil on the transformer connected with the battery is 



