American telegraphy and encyclopedia of the telegraph; systems, apparatus, operation (1909)
Maver, William, jr. [from old catalog] · New York, Maver publishing company · leaf 424
ystem whether the Morse system is idle or working. In Fig. 267 the phone isshown as it appears in prac-tice. The magnetic coil isshown in Fig. 268. Thissystem may be used on cir-cuits of from one hundred to one hundred and fifty miles in length, and it is not limited to any stated number… … THE PHONE. FIG. 268
Telegraph
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