American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 313
EDISON-SMITH DUPLEX. The neutral relay is placed in the circuit of battery b, within the contact points,cc oi the pole-changer, so that it is not affected by the reversals of the battery, thedirection of the current between those contacts being always the same. The relays nr, pr are wound singly.…
Telegraph
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