. American telephone practice . LTIPLE SWITCH-BOARD. 327 figure illustrating- the Kellogg system. They are associated with the*line lamp circuit in practically the same manner as in the WesternElectric system. The operation of these will, therefore, be madeclear from the description of the Western Electric pilot circuitalready given in connection with Fig. 267. The Kellogg, Company also applies the pilot feature to the super-visory signals in such a manner that a pilot lamp will light on anyposition whenever the subscriber who originated the call hangs uphis receiver. In other words, the pilot
. American telephone practice . LTIPLE SWITCH-BOARD. 327 figure illustrating- the Kellogg system. They are associated with the*line lamp circuit in practically the same manner as in the WesternElectric system. The operation of these will, therefore, be madeclear from the description of the Western Electric pilot circuitalready given in connection with Fig. 267. The Kellogg, Company also applies the pilot feature to the super-visory signals in such a manner that a pilot lamp will light on anyposition whenever the subscriber who originated the call hangs uphis receiver. In other words, the pilot lamp will light whenever thesubscriber to whose line the answering plug is connected hangs uphis receiver. The night alarm bell will also sound if the switch con-trolling it is in the proper position. This is readily accomplished byplacing in series with the supervisory lamp associated with the an-swering plug a pilot relay which controls the pilot lamp for thatposition, it being understood, of course, that this lamp is common. SubS .STATION FIG. 271. -STROMBERG-CARLSON TWO-WIRE MULTIPLE SWITCH-BOARDLINE CIRCUIT. to the circuits of all the answering supervisory lamps on thatposition. In a common portion of the circuit belonging to all of the super-visory pilot lamps in the office is placed a night alarm pilot relay inthe same manner as the night alarm relay was applied to all the linepilot lamps. This supervisory night alarm is useful at night for call-ing the attention of the operator to the fact that a disconnection isdesired on some portion of the board. The Stromberg-Carlson Company during the last few years hasinstalled in a number of places a two-wire multiple common batterysystem, the line circuit of which is shown in Fig. 271. In this cir-cuit the cut-off relay, C, is provided with two coils differentiallywound, so that when the two windings are traversed by equal cur-rents in opposite directions no effect will be produced upon the windings are put on the co
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