The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 165
no. 5 RINGINGBATTERY. RETURN WIRE Vig. 153 ant at the latter station take off their receivers, they will bein communication with each other. It is evident that more than one pair of wires may be inuse at the same time, and also that a number of, or all, thestations may be connected together at…
Telephone
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