Telegraph repeaters 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, limiting the distance a message could travel. Repeaters remedied that problem by detecting a weak signal and using a local power source to re-energize and re-transmit the signal down the line.
This unusual repeater was made by noted electrical inventor Moses Farmer and is one of the devices bequeathed to the Smithsonian by his daughter Sarah in 1917. The records indicate the repeater was "devised and used by Farmer" in experiments related to underwater telegraphy. The unit features a four-plate compound magnet and a set of electromagnetic coils connected by a series of wires.
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