218 



OUR PHYSICAL WORLD 



little German town, who in 1860 applied the name " telephone" 

 to his invention. But Alexander Graham Bell is looked upon as 

 the real inventor of the telephone, although a few hours after 

 he had filed his papers at the Patent Office in Washington (1876), 

 Elisha Gray, of Chicago, filed his papers covering the invention 

 of an instrument for a similar purpose. Bell's was the more 

 practical as well as the prior invention, and the present instru- 

 ment is still called the Bell telephone, although his original 

 device has been greatly modified. 



Bell, the son of an Edinburgh clergyman, received a literary 

 education. As a young man he emigrated to the United States 

 and became instructor in an institution for deaf-mutes in Boston. 



This experience centered 

 his attention on sound and 

 hearing. He realized that, 

 in hearing, the ear drum is 

 made to vibrate by waves 

 of sound, and that, in 

 speaking, such waves are 

 caused by the vibrations of 

 the vocal chords. He con- 

 ceived the idea that such 



FIG. 88. Diagram of a telephone receiver 



sound waves might be produced by a vibrating membrane 

 operated by an electric current in harmony with another mem- 

 brane at some distance, whose vibrations were produced by the 

 voice of a person speaking against it. He used to remark that 

 it was well he had received a literary rather than a scientific 

 education, for if he had known anything about electricity he 

 would never have had the audacity to think such a thing possible. 

 He was, however, encouraged by Joseph Henry, of Philadelphia, 

 then the American master of electrical science. 



In the early instruments the transmitter and the receiver 

 were much alike. Each consisted of a thin steel diaphragm 

 mounted near one end of a soft iron core, wound with insulated 

 wire (Fig. 88). One of the two wires of the operating battery 



