. American telephone practice . he receiver israised, the current from the battery at central, which tends to passthrough the storage battery, will meet with a considerable counterE. M. F., which will compel most of the current to pass from theline wire, 2, through the secondary, S, receiver, hook lever, trans-mitter and primary, P, to the line wrire, 3. The transmitter will therefore receive current from the battery, i,sufficient to operate it, and yet it will be operating with all the ad-vantages to be derived from a local circuit and induction coil; for,although the current operating it com
. American telephone practice . he receiver israised, the current from the battery at central, which tends to passthrough the storage battery, will meet with a considerable counterE. M. F., which will compel most of the current to pass from theline wire, 2, through the secondary, S, receiver, hook lever, trans-mitter and primary, P, to the line wrire, 3. The transmitter will therefore receive current from the battery, i,sufficient to operate it, and yet it will be operating with all the ad-vantages to be derived from a local circuit and induction coil; for,although the current operating it comes from the central office, anyfluctuations in this current caused by the transmitter will passthrough the low-resistance battery, d, which will act in this casevery much in the same manner as a condenser. COMMON BATTERY SWITCH-BOARDS. 303 The same general designs of switch-board cabinets as are usedin small magneto-switch-boards are often made to serve for com-mon batten- boards, their dimensions and construction being changed. FIG. 253—COMMON-BATTERY SWITCH-BOARD FOR SMALL EXCHANGES. sufficiently to accommodate the different class of apparatus. A com-plete switch-board adaptable to exchanges, having not over onehundred lines, is shown in Fig. 253. CHAPTER XIX. COMMON BATTERY SUB-STATION EQUIPMENT. The essential features of the sub-station equipment for commonbattery work are the speech-receiving and transmitting apparatus,or receiver and transmitter; the call receiving apparatus, or ringer,the switch-hook for alternately bringing the talking apparatus andthe call receiving apparatus in proper relation with the line; and adevice, usually a condenser, for preventing direct currents from flow-ing over the metallic circuit of the line when the telephone is not inuse, but adapted to allow alternating currents to pass for the purposeof ringing the bell. It has been shown in the three preceding chapters that the condi-tions required of the sub-station in order to bring about the o
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