The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 186
d drop it, and the operator would never know whetherthe subscriber required attention or whether he was being rung up byanother operator upon another multiple. Also it is clearly necessary toprovide an engaged test. The switch-springs employed are of a somewhat different form to anywe have… … Figure 135. wire, and the back part for the B line connection. Two springs of theswitch-springs are placed opposite each other, and upon the insertion of apeg are connected together by the neck of the peg. The third spring ofthe switch-spring is the A line spring. The connections of the pegs…
Telephone · Postal service
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