The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 75
er, in order to prevent its sticking—due to residual magnetism. When the shutter drops, the small insulatedspring S is brought into contact with the pin P, which is connected to thebase or brass foundation of the instrument, and this contact is employed 6o Indicators and Relays. to ring a bell at…
Telephone · Postal service
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