The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 109
wasted incalling off each of the connections to the National. In order to avoid thisthe two inner contacts of the junction switch springs (Figure 8i) areconnected to an earthed battery, which, when the peg is withdrawn, sendsa current along both lines to the National, where it passes through… … ^£E: Figure 8i. two bridging coils are joined in series. These coils are wound to looo »each, and have a very high self-inductance. The coils are wound uponHn iron core, and are surrounded by iron closed at both ends, thus forminga magnetic circuit wholly of iron. The self-inductance possessed by…
Telephone · Postal service
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