Henning telegraph relay

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Telegraph relays 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, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
This relay was made by Robert Henning, superintendent of the Western Union machine shop in Ottawa, IL. Prior to that Henning worked as manager for the Caton Telegraph Instrument Shop, established by John Dean Caton in Ottawa. Caton had helped found the Illinois & Mississippi Telegraph Company in 1849 and sold out to Western Union in 1867. Apparently the Instrument Shop (and Henning) went to Western Union with the deal.
Currently not on view
date made
ca 1870
Henning, Robert
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
plastic (overall material)
overall: 4 1/4 in x 9 in x 4 1/4 in; 10.795 cm x 22.86 cm x 10.795 cm
ID Number
catalog number
accession number
Credit Line
from Pennsylvania Railroad Company
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History


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