The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 124
onding peg is taken up and inserted into a Bcircuit of the required section. The combination key is then raised, thusputting the visuals at normal. The B circuits are accommodated uponthe upright part of the transfer board. The combination key consists of thirteen springs arranged in two sets.These… … are connected to the A circuit, and the outer ones to the operatorssecondary; thus when the ebonite moves upwards and pushes apart thelong springs, the operators telephone is connected to the circuit. Atthe same time the central pair of springs make contact, thus com-pleting the operators primary…
Telephone · Postal service
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