The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 78
Tablet. 63 When the lever is at rest the two halves make contact with the twobottom springs. The four-way peg carries a projection which fits thetop switch-spring, thus preventing the peg being inserted-upside down.The primary circuit is from either speaking battery according to whichposition the… … Figure 52, through the bottom left hand switch-spring to the left hand side of thedivided lever, through the left hand bottom spring back to the battery.It will be seen that when the lever is depressed the primary circuit isbroken, thus preventing the battery from being run down. The…
Telephone · Postal service
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