. American telephone practice . of the wall board, the batteryresting on a cast iron shelf secured to the wall board and beingcompletely exposed for inspection by the removal of the methods of fastening the box have been used, but one,consisting of two clamps on the inner side of the battery boxadapted to engage two similar clamps secured to the back board,has come into wide use. The box is engaged or disengaged by adownward or upward motion with respect to the back board. LOCAL BATTERY SUB-STATION EQUIPMENTS. 141 The complete circuits of the bridging belF telephone set areshown in
. American telephone practice . of the wall board, the batteryresting on a cast iron shelf secured to the wall board and beingcompletely exposed for inspection by the removal of the methods of fastening the box have been used, but one,consisting of two clamps on the inner side of the battery boxadapted to engage two similar clamps secured to the back board,has come into wide use. The box is engaged or disengaged by adownward or upward motion with respect to the back board. LOCAL BATTERY SUB-STATION EQUIPMENTS. 141 The complete circuits of the bridging belF telephone set areshown in Fig. 116. This shows the arrangement used in practice,embodying the simplified circuits shown in Figs, in and 112. Itwill be seen that the bell, P, is permanently bridged across the twosides of the line between the binding posts 1 and 2, the connectionsbeing made through the hinges of the bell box. The generator, G,is in a second bridge circuit, normally open, but adapted to when the generator is operated. / ? &. FIG. 116.—COMPLETE BRIDGING BELL TELEPHONE CIRCUIT—COIL IN BASE OF ARM. In Fig. 117 are shown the complete working circuits of a seriestelephone wall set in which the induction coil is mounted in the bellbox rather than in the base of the transmitter arm. Fig. 118 showsthe circuits of a bridging telephone using a similar practice of mounting the induction coil in the bell box ratherthan in the base of the transmitter arm is probably, all things con-sidered, the best. There is no good reason why the coil should bemounted in the base of the transmitter arm and the circuit wiring 142 AMERICAN TELEPHONE PRACTICE. of the box is made somewhat simpler by mounting the coil in thebell box. Since the use of the dry cell has become very common for localbattery telephones, a new type of wall set has come into voguewherein the call bell, generator, switch-hook, induction coil andbatteries are all mounted in a single box divided off into compart-ments
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