Clark telegraph relay

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.
George C. Maynard, the curator who collected this piece in 1897, showed this and a similar relay to Dr. James J. Clark who, “examined these relays and said they were made by him about 1846 in Philadelphia. [They] represent the first big step in relay construction, after the 'big magnets' first used by [Samuel] Morse. They were originally [mounted] in a box with the adjusting screws projecting. The Clarks (J. J. and his father) made and sold many of these relays. [The Clarks] supplied [Henry] O'Rielly and all the southern lines."
Currently not on view
Object Name
telegraph relay
date made
Clark, James J.
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
ivory (overall material)
silk (overall material)
copper (overall material)
paper (overall material)
overall: 6 in x 7 1/2 in x 6 in; 15.24 cm x 19.05 cm x 15.24 cm
ID Number
catalog number
accession number
Telegraph Relays & Repeaters
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
from Western Union Telegraph Co.
Additional Media

Visitor Comments

Add a comment about this object

**Please read before submitting the form**

Have a comment or question about this object to share with the community? Please use the form below. Selected comments will appear on this page and may receive a museum response (but we can't promise). Please note that we generally cannot answer questions about the history, rarity, or value of your personal artifacts.

Have a question about anything else, or would you prefer a personal response? Please visit our FAQ or contact page.

Personal information will not be shared or result in unsolicited e-mail. See our privacy policy.

Enter the characters shown in the image.