The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 75
Figure 47. Figure 48. thin sheets of Iron, in order to prevent lipes of force from straying outinto the surrounding air. This prevents induction from one indicator toadjacent ones. If this were not done it would be possible to overhearconversations from one circuit to another whose indicator was… … Figure 49. At the subscribers end the permanent current passes through a relaywhich is biassed against it. The ring is thus produced by augmenting thecurrent through the relay by joining up a battery at the exchange. The relay employed is shown below in Figure 49, It consists of anelectro-magnet…
Telephone · Postal service
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