. American telephone practice . By means of theseplugs and the jacks, a, b, c or d, the Wheatstone bridge may be con-nected between any two of the four limbs of the inside and outside 638 AMERICAX TELEPHONE PRACTICE. line, or, by inserting one of the plugs in the ground jack, g, betweenany one of the limbs and ground. As will be seen the two testing plugs in Fig. 8 are normally con-nected in series through a battery of five cells and through a relayand key, the purpose of which is to ascertain whether or not therelay will be operated when the key, K, is closed over whateverresistance is connec
. American telephone practice . By means of theseplugs and the jacks, a, b, c or d, the Wheatstone bridge may be con-nected between any two of the four limbs of the inside and outside 638 AMERICAX TELEPHONE PRACTICE. line, or, by inserting one of the plugs in the ground jack, g, betweenany one of the limbs and ground. As will be seen the two testing plugs in Fig. 8 are normally con-nected in series through a battery of five cells and through a relayand key, the purpose of which is to ascertain whether or not therelay will be operated when the key, K, is closed over whateverresistance is connected between the circuit of the two plugs. When, however, the key, K, is thrown into its alternate posi-tion, whatever resistance is between the two plugs represents theunknown resistance on the Wheatstone bridge arrangement, andmay be measured accordingly. The voltage of the battery suppliedto the Wheatstone bridge may be varied by inserting the plug, p,into one of the several jacks connected with the cells of the battery. OO. WHEATSTONE BRIDGE. FIG. PLUG CIRCUIT. It is evident that if it is wished to measure the resistance betweenthe ring side of the outside line and ground, one of the bridge plugswill be inserted in the jack, c, while the other will be inserted in theground jack, g. The more modern wire chiefs desk equipment used by many ofthe Bell companies are shown in Figs. 468, 469, 470, 471 and Fig. 468 is shown the test trunk leading from the wire chiefsdesk to the test plug adapted to connect with the arrester springsat the main distributing frame. Remembering that the two outsidesprings of the arrester lead to the switch-board end of the line, whilethe two inside terminals lead to the outside line, it will be seen thatwhen the connection is thus made with a line, the jack, /, affordsmeans for connecting directly with the switch-board line circuit, WIRE CHIEFS EQUIPMENT. 639 while the jack, /, affords means for connecting with the outsideline circui
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