The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 187
condmultiple switch-spring. The battery which is used to lock the self-restoring indicator is also used for giving the engaged test. The circuitof the battery is along the battery lead through the two springs con-nected together by the neck on to the test wire, and thence through therestoring coil… … Figure 136. The operating connections are very similar to those previously de-scribed, and so far as the engaged testing is concerned are precisely thesame. The middle of the receiver is earthed exactly as in the connectionspreviously described; thus by touching the front barrel with the tip of…
Telephone · Postal service
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