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.

Date Made: 1876Used In A Demonstration: 1876

Inventor: Bell, Alexander GrahamMaker: Bell, Alexander Graham

Location: Currently not on view

Associated Place: United States: Massachusetts, SalemUnited States: Massachusetts, Boston

Subject: TelephoneMagnet

Subject:

See more items in: Work and Industry: Electricity, Communications, American Stories exhibit

Exhibition:

Exhibition Location:

Credit Line: from American Telephone & Telegraph Company

Data Source: National Museum of American History

Id Number: EM.308214Catalog Number: 308214Accession Number: 70856

Object Name: telephonebox telephoneOther Terms: box telephone; Telephones; Transmitter/Receiver

Physical Description: wood (parts material)iron (magnet material)brass (hardware material)iron (diaphram material)mica (insulator 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

Guid: http://n2t.net/ark:/65665/ng49ca746ab-f6ef-704b-e053-15f76fa0b4fa

Record Id: nmah_704159

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