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 includes a marble base and was made by Charles T. Chester of New York City. The electromagnet coils are fixed but the steel core can be moved to adjust the strength of the magnetic field.
A 4-pin brass shell with plastic insulator, tipped T-shaped envelope. "S" stamped on insulator. Stamped on envelope: "Moorhead Audion / San Francisco / 217957"; on base: "Marconi / [globe logo] / Trade Mark / Fleming Patent No 803684" and "De Forest Audion / U.S. Patent Nos. 841387-879532 / Sold only for Amateur / and Experimental use." Reference: Tyne, "Saga of the Vacuum Tube," pages 172-175.
