. American telephone practice . t them. Tt frequently happens, how-20 306 AMERICAN TELEPHOXE PRACTICE. ever, that in making changes in line connections, perhaps in a man-hole or on a pole, the two sides of the line will be transposed, which,of course, subjects a receiver, previously connected properly, to cur-rent in the wrong direction and makes necessary a trip of the in-spector to that station. This arrangement has another objection in that a receiver properlyadjusted for maximum efficiency on a line having, a certain currentstrength, may not be properly adjusted for a line having a stronge
. American telephone practice . t them. Tt frequently happens, how-20 306 AMERICAN TELEPHOXE PRACTICE. ever, that in making changes in line connections, perhaps in a man-hole or on a pole, the two sides of the line will be transposed, which,of course, subjects a receiver, previously connected properly, to cur-rent in the wrong direction and makes necessary a trip of the in-spector to that station. This arrangement has another objection in that a receiver properlyadjusted for maximum efficiency on a line having, a certain currentstrength, may not be properly adjusted for a line having a strongercurrent. Frequently when placed on a very short and therefore lowresistance line, the magnetic attraction of the cores is sufficient topull the diaphragm into contact with the pole pieces, thus destroyingall possibility of its vibrating. The prevention of the flow of direct current through the receiverhas been solved in a number of ways, perhaps the most common waybeing that employed in instruments made by the Western Electric. FIG. 256.—WESTERN ELECTRIC SUB-STATION CIRCUIT. Company for the various Bell companies. In this arrangement,which is shown in Fig. 256, the receiver is included in a local cir-cuit which also includes, when the hook is raised, one winding of aninduction coil, and a two-microfarad condenser, which is also em-ployed for transmitting the ringing currents. When the hook is de-pressed by the weight of the receiver there is no path for direct cur-rents between the limbs, a and b, of the line on account of the pres-ence of the condenser. The only path for alternating currents isthat through the condenser and bell. When the receiver is removedfrom the hook, however, direct current may flow from the centraloffice over the limb, a, of the line through the 17-ohm winding of theinduction coil and the transmitter to the limb, b, of the line. Thisflow of current causes the operation of relays for signaling at thecentral office, and also supplies the transmitter wit
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