The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 87
sists ofseven insulated brass springs, in two sets of four and three springs,mounted upon a brass foundation. The lower four springs consist of twoouter springs of different length and two inner springs making contactwith them. The short spring comes into contact with the tip, and thelong spring… … Figure 61. thus breaking confact with the lower spring. This cuts the local per-manent current circuit. The insertion of the peg also causes the twosprings connected to the trunk to break contact with the inner springs,and this cuts the indicator and main permanent current battery out ofthe…
Telephone · Postal service
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