The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 205
cuit is then entered by means of the speaking key. Thisvirtually divides the circuit into two. The disengaged side is joined up to thepermanent current relay, and thus the terminal office is not disturbed. Anycall would be received upon the relay and would then be answered by theintermediate office… … Figure 145. terminal office removes the peg the exchange galvanometer is deflected. Inorder to receive calls a magneto bell is joined in parallel with the self-restoringindicator and exchange galvanometer. If the intermediate office wishes to enter the circuit to speak to one of theterminal offices…
Telephone · Postal service
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