The telephone system of the British post office. A practical handbook (1901)
Herbert, Thomas Ernest · London, New York, Whittaker and Co. · leaf 104
co/v/vecrz/va Figure 76. permanent current, which also deflects the needle to the right. When thepermanent current is stopped by the removal of the receivers, the shutterdrops, and calls the attention of the operator. There are three self-restoring indicators attached to the three circuitsbetween… … OFi FtM Tons FlGUBE 77.National Company come to the two outer springs of an eight-point switch-spring, In the normal condition these two lines pass through the back or■line coil of the self-restoring indicator by means of the inner springs(Figure 77). A ring from the Nationtvl causes the shutter to…
Telephone · Postal service
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