The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 154
,in addition to the connections given by the last-named switchit is desired to give means of communication between thetwo end stations, an Intermediate Through Switch is used.The extra bell at the middle station is then connected as ashunt to the hues when connected through, so that a signalmay be… … Fig. 145 superseded other forms which were in use, owing to its neat-ness, simplicity, and fewer working contacts. It is con-structed on the principle of the old double-tapper key usedin telegraphy, by means of which reversed currents can besent to line from a single battery. For the switch, two…
Telephone
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