Modern practice of the electric telegraph : a handbook for electricians and operators (1874)
Pope, Frank L., 1840-1895 · New York : D. Van Nostrand · leaf 29
y. This arrangement is called an electro-magnet. (34.) 33. If the iron is very soft and pure it loses its mag-netism instantly upon the cessation of the current, butif impure, or if hardened by hammering or turning, itretains a certain amount of residuary magnetism, espe-cially after it has been… … 34. Electro-Magnets are generally made in a Uform, two bobbins or spools, a a (fig. 8), being filled with covered copper wire, and thesoft iron cores, c c, passing throughthem, fixed upon a connecting bar,« 5, also of soft iron, as shown in thefigure. The two spools, a and a, arevirtually…
Telegraph
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