Signedon back plate: WESTERN ELECTRIC
Inscribedon base: No 22A / 100 OHMS
on back plate: JULY 21 1903 MADE IN USA
FunctionThis telegraphic instrument was used as control relay. It could be used to control the current flow between other telegraphic instruments and switchboards. When a current flowed through the magnet, it would attract the metal plate in front. When the current ceased to flow, the plate would return to its resting position. The effect was that of opening and closing a switch.
ProvenanceFrom the Department of Physics, Lyman Laboratory, Harvard University.