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.
So-called “pony” relays like this unit made by Manhattan Electric Supply Co., serviced private lines and shorter branch circuits. The resistance of a given pony relay varied depending on the length of the circuit. This 10 ohm pony relay would have been used on circuits up to about 7 miles in length.
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.