Man's physical universe

xanabras

514 MAGNETISM AND ELECTRICITY

The telephone receiver contains a

permanent horseshoe magnet with

coils about each pole, through which

the incoming current passes, causing

the magnetic field of the magnet

to fluctuate and thus altering its

pull upon a thin sheet, or diaphragm,

of iron near by. The resulting

oscillation of the diaphragm

transmits vibrations to the air outside,

and in this way produces

sound.

In the United States

today the

telephone messages sent out are

twice the number of letters and

postcard messages, the total num-

FiG. 249. Broadway and John

Street, New York City in 1890.

(Courtesy of the American Telegraph

and Telephone Company.)

ber of messages exceeding 30,000,-

000,000 annually. The 20,000,000

telephones in the United States

today represent approximately 60

per cent of the telephones of the

world. In 1939 New York City

alone had more telephones than

France, Spain, Russia, Japan, or

Sweden.

It is of interest to note that Elisha

Gray invented the telephone at

nearly the same time that Bell did

but that Bell was granted the

patent. However, Gray improved

the telephone and founded the

Western Electric Manufacturing

Company, which at the present

time manufactures most of the

equipment used in the telephone

industry.

F~IG. 250. Bruad\va\- and John

Street, New York City in i920.

(Courtesy of the American Telegraph

and Telephone Company.)

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