The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 134
circuit terminated upon a switch sectionis illustrated in Figure loi. It will be seen that the loop passes to the longand short springs of an eight-point switch-spring, the three top springs ofwhich are used for signalling, as in the case of the ordinary transfer circuits.Across the loop is placed,… … Figure 101. which are connected together to a visual indicator, having an earthedbattery joined to it. In the normal state of affairs, the negative pole ofthe battery A at the Post OiBce passes through the relay, bottom andcentral springs through the visual and along both lines in parallel.…
Telephone · Postal service
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