American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 220
hen the home relay, its spring being placed at a very low tension,does not respond to the opening and closing of the home transmittero THE POLAR DUPLEX.The Polar Duplex. l8i This duplex involves in its operation, among other principles, this one, that, whena current of electricity flows in a coil… … For instance, if, as in Fig. 147, the current circulates around the core from lefttonight, as indicated by the arrows, the left hand end will be a north pole and the FIG. 148,
Telegraph
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