The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 155
heir inner springs are used to join up theindicators. The inner springs are connected to the indicators. Upon thesuperimposed circuit it is possible to work with permanent current, sincecircuit at either end is connected directly to each other, via the trunklines. This is accordingly done. The form… … real size.Figure 117. permanent current working. The chief point of difference consists in theabsence of the permanent magnet which magnetises the armature in thecase of the polarised form. The armature of the non-polarised relay is ofsoft iron, and passes over the projecting core of the right hand…
Telephone · Postal service
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