. An analytical compendium of the various branches of medical science, for the use and examination of students. Anatomy; Physiology; Surgery; Obstetrics; Medicine; Materia Medica. GALVANISM, OR VOLTAIC ELECTRICITY. 27 Fig. 14. fact had been long known that electricity was capable of inducing and destroying magnetism, as witnessed in the effects of lightning on the compass-needle, it was not until the year 1819 that the laws of these phenomena were established by CErsted, and the science of electro-magnetism truly developed. It is found that if a galvanic current be set in motion near a magneti
. An analytical compendium of the various branches of medical science, for the use and examination of students. Anatomy; Physiology; Surgery; Obstetrics; Medicine; Materia Medica. GALVANISM, OR VOLTAIC ELECTRICITY. 27 Fig. 14. fact had been long known that electricity was capable of inducing and destroying magnetism, as witnessed in the effects of lightning on the compass-needle, it was not until the year 1819 that the laws of these phenomena were established by CErsted, and the science of electro-magnetism truly developed. It is found that if a galvanic current be set in motion near a magnetic needle, the latter will arrange itself across the current, so that its axis may be perpen- dicular to the wire. When an electric current is passed at right angles to a piece of iron or steel, the latter acquires magnetic polarity, either temporary or permanent; the direction of the current determining the position of the poles. This effect is very much increased by causing the current to circulate a number of times around the bar, which soon acquires extraordinary magnetic power. A piece of soft iron in the form of a horseshoe, surrounded thus by a coil of copper wire, insulated by being covered with silk, may be made to become so highly magnetic simply by connecting the two ends of the iron with a small battery of a single pair of plates, as to be capable of sustaining a very heavy weight. As electricity can produce a magnetic influence, in the same manner it is found that magnetism can call into activity electric currents. \{ the two ex- tremities of the coil of the electro-magnet just de- scribed, be connected with a galvanoscope, and the iron magnetized by the application of a steel horseshoe magnet to the ends of the bar, a momentary current will be developed in the wire, and pointed out by the movement of the needle. On removing the magnet, whereby the polarity of the iron is at once destroyed, a second current will become apparent, but in the opposite direction to that
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