History, theory, and practice of the electric telegraph (1866)
Prescott, George B.(George Bartlett),1830-1894 · Boston, Ticknor and Fields · leaf 62
Fig. 25. Fig. 26. first; so that if the bar had.been straightened, the two heliceswould have formed but one, both right-handed, or both left-handed.A feeble electric current, such as that produced by a single pair ofcopper and zinc plates, is sufficient, on being transmitted throughthe wire, to…
Telegraph
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