Experimental science. Elementary, practical and experimental physics (1890)
Hopkins, George M. (George Milton), 1842-1902 · New York, Munn & co. · leaf 501
r the key lever throws the armature back intocontact with the magnet. This is a simplified form of Bre-guets exploder, used in firing blasts in mines, and althoughmuch smaller than the apparatus referred to, it is capableof ringing a polarized bell over fifteen or twenty miles ofwire, and will give… … bell, presently to be described. In this apparatus like polesof the magnets must oppose each other, and the clampingpieces and screws should be of non-magnetic material. Iftwo magnets do not produce a current of sufficient strengthfor the intended use, two more may be added. In this form of…
Physics · Lantern projection · Electric apparatus and appliances
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