The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 125
shown in the upper partof Figure 94. The inner spring on the left is not used at all. Thebottom springs are arranged exactly like a ringing key, and when theebonite descends, forcing the long springs apart, they leave the innersprings and make contact with the outer ones. Of these six springs… … Figure 95. The connections of an A circuit are shown in Figure 96. It will beseen that the speaking circuit passes from the line switch-springs to thepeg at the transfer board, whence if is teed off to the long springs of thecombination key. This provides a method of connecting the…
Telephone · Postal service
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