Miniature box 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.
Box relays were most often used by linemen or station operators for testing purposes or where a local battery was not available. The covering box acted as a resonator that amplified the sound of the relay’s light-weight armature, making the signal audible without a sounder. This unusual miniature unit was made by the donor and was reportedly used briefly on the line between Pittsburgh and Baltimore.
Currently not on view
date made
Physical Description
wood (overall material)
steel (overall material)
brass (overall material)
cloth (overall material)
overall: 2 in x 5 1/2 in x 2 1/4 in; 5.08 cm x 13.97 cm x 5.715 cm
ID Number
catalog number
accession number
Credit Line
from C. I. Ways
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History


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