The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 190
giving to every subscriber, besides hisordinary circuit to the exchange, access to a second circuit. This secondcircuit is common to about fifty subscribers, any one of which, by depres-sion of a key, may pla£e himself upon it. At the exchange the circuitterminates upon the speaking apparatus of… … eJtSl ivnn-xipuEa Figure 138. Since all instructions as to connections and disconnections are givenover the call wire, it is clearly unnecessary to provide indicators orspeaking keys at the exchange. The subscriber rings up his correspondenthimself and thus speaking keys are not required. In the…
Telephone · Postal service
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