Relay used at telegraph receiving stations, particularly those operating on long connecting lines. Often signals received over long lines were too weak to operate the receiving instruments directly so the relay served as a very sensitive switch to connect a local battery to the receiving instruments.

A polarized relay incorporated a permanent magnet in its design. Because this type of relay depended completely on magnetic effects, it was faster and more sensitive in operation than a non-polarized relay which incoporated a mechanical return spring.

Made by Siemens Halske & Company, London. Used at Melbourne Observatory

Physical Description

Wooden base. Brass vertical cylindrical case with glass top. Brass terminals around base.

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