Our museum is temporarily closed to support the effort to contain the spread of COVID-19. Read a message from our director, and check our website and social media for updates.

Gray telegraph relay patent model

Gray telegraph relay patent model

<< >>
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 constructed early in 1867 by noted electrical inventor Elisha Gray to accompany a patent application. He received US Patent 69,424 later that year for an improved telegraph relay. Gray's idea was to use a second set of electromagnet coils rather than a spring to retract the armature after a signal pulse. He wrote that the pulse's strength could vary so much that a relay's spring needed constant adjustment. His design compensated automatically for the variation in pulse strength.
Currently not on view
Object Name
telegraph relay
Object Type
Patent Model
date made
Gray, Elisha
Physical Description
wood (overall material)
brass (overall material)
plastic (overall material)
cloth (overall material)
overall: 4 1/2 in x 11 1/2 in x 5 3/8 in; 11.43 cm x 29.21 cm x 13.6525 cm
ID Number
catalog number
accession number
patent number
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History
Nominate this object for photography.   

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.


Add a comment about this object