The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 126
Fig. 96 SUB-STATION APPARATUS 103 to the centre of a brass spring a a, one end of which bearson the piece b, and the other end on one of the brass piecesc or d, according to the direction in which the handle is
Telephone
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