Clark telegraph repeater patent model

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Telegraph repeaters amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, limiting the distance a message could travel. Repeaters remedied that problem by detecting a weak signal and using a local power source to re-energize and re-transmit the signal down the line.
This non-operating model was submitted to the U.S. Patent Office by inventor James J. Clark of Philadelphia. In July 1860, Clark received patent #29247 for his "Improvement in Telegraphic Repeaters." Clark added an extra magnet to the local circuit of the repeater. Charles Davis and Frank Rae described Clark's repeater in 1877, noting that by then it was obsolete. "The relays have [longer armature levers that respond to extra magnets but] the sounders do the repeating. ... It was very good and was extensively used at one time."
Currently not on view
date made
Clark, James J.
Physical Description
brass (overall material)
wood (overall material)
cloth (overall material)
ivory (overall material)
steel (overall material)
copper (overall material)
overall: 4 in x 12 1/4 in x 12 in; 10.16 cm x 31.115 cm x 30.48 cm
ID Number
catalog number
accession number
patent number
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Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History


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