The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 94
m of the British Post Office. 79 It CHAPTER Xni.Operating Connections.is necessary to provide a means of ringing National subscribers. Tliis is effected by means of a ringing key, which cuts off the blaclc pegand joins a generator to the red one. The current passes over the junctionto the… … Figure 67. sufficiently strong to both reverse the deflection and close the local circuit.The ringing keys (Figure 67) consist of a brass block carrying fourinsulated springs and two insulated contact studs. The two inner springsnormally make contact with the studs, and project beyond the brass…
Telephone · Postal service
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