Alexander Graham Bell's Large Box Telephone

Description
One of two telephones used by Alexander Graham Bell in a demonstration that took place between Boston and Salem, Massachusetts on November 26, 1876. Critical features are the iron diaphragm (seen as a black circular disc mounted on the vertical wooden support), two electromagnets (seen in white, facing the diaphragm) and a horseshoe permanent magnet (lying horizontal, pressed against the electromagnets).
When used as a transmitter, sound waves at the mouthpiece cause the diaphragm to move, inducing a fluctuating current in the electromagnets. This current is conducted over wires to a similar instrument, acting as a receiver. There, the fluctuating current in the electromagnets causes the diaphragm to move, producing air vibrations that can be heard by the ear. This was a marginal arrangement, but it worked well enough to be employed in the first commercial services in 1877. The magneto receiver continued to be used, but the transmitters were soon replaced by a carbon variable-resistance device designed by Francis Blake and based on a principle patented by Thomas Edison.
Object Name
telephone
box telephone
date made
1876
used in a demonstration
1876
patentor
Edison, Thomas A.
inventor
Bell, Alexander Graham
Blake, Jr., Francis
maker
Bell, Alexander Graham
Physical Description
wood (parts material)
iron (magnet material)
brass (hardware material)
mica (diaphram material)
Measurements
overall: 6 1/4 in x 7 1/2 in x 12 1/2 in; 15.875 cm x 19.05 cm x 31.75 cm
Associated Place
United States: Massachusetts, Salem
United States: Massachusetts, Boston
ID Number
EM*308214
catalog number
308214
accession number
70856
subject
Telephone
Magnet
Communications
American Stories exhibit
See more items in
Work and Industry: Electricity
American Stories exhibit
Exhibition
American Stories
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
from American Telephone & Telegraph Company
Additional Media

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