Greeley main-line 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.
“Main line” relays like this unit were common. Typically made with a resistance of 150 ohms, main line relays served on major intercity circuits. According to George C. Maynard, the curator who collected this piece in 1891, "This specimen seems to be a very slightly modified version of the Western Union Relay No. 2 of the Tillotson Company which was introduced in a 150 Ohms model about 1880-1881 at $8.50. As late as 1893 the E. S. Greeley Co. was still using the Tillotson illustration of 1880-1881. However the caption had been changed to 'Improved Western Union Relay'. ... The armature or lever in this model is the old style of two-piece construction. A bar across the poles of the magnet is attached to the lever [instead of a single-piece lever]."
Currently not on view
date made
E. S. Greeley & Company
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
plastic (overall material)
overall: 3 1/2 in x 8 3/4 in x 4 1/2 in; 8.89 cm x 22.225 cm x 11.43 cm
ID Number
accession number
catalog number
Credit Line
from the E. S. Greeley Co.
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History


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