The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 217
OPCRATINO CONNECTIONS. Figure 146. when another circuit is formed from the positive pole of the battery throughthe coil of the transfomer T„ and cut-off relay R, along the B line throughthe subscribers transmitter and primary of his induction coil, along the A lineand back to the battery through…
Telephone · Postal service
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