. Bulletin. Science. Figure 43.—Henry's quantity electromagnet. From American Journal of Science, 1831, vol. 19, p. That an electric current not only will cause a magnet to move but can create a magnet was the discovery of Arago,''* who found that a current-carrying conductor will attract iron filings, and that if wire is wound upon a glass tube, and a needle placed inside the tube, the needle will become a magnet when current is passed through the wire. Similar experinients performed by Arago together with Ampere led to the latter's circu- lating current theory of magnetism.^' Instead o
. Bulletin. Science. Figure 43.—Henry's quantity electromagnet. From American Journal of Science, 1831, vol. 19, p. That an electric current not only will cause a magnet to move but can create a magnet was the discovery of Arago,''* who found that a current-carrying conductor will attract iron filings, and that if wire is wound upon a glass tube, and a needle placed inside the tube, the needle will become a magnet when current is passed through the wire. Similar experinients performed by Arago together with Ampere led to the latter's circu- lating current theory of magnetism.^' Instead of using a steel core in the form of a bar or cylinder, an English, self-taught physics teacher named William Sturgeon ™ used a horse-shoe-shaped soft iron core atid obtained a much more concentrated magnetic field (fig. 41). In 1825 the Society for the Encouragement of Arts, Manu- facture, and Commerce awarded Sturgeon a medal and a financial prize for this improvement on the electro- magnet. By winding a bare wire on a varnished core so that the current passing through the wire would not short out. Sturgeon succeeded in producing an electro- magnet that would support a weight of nine pounds 8* Dominique Arago, "Experiences relatives a I'aimantation du fer et de I'acier par Faction du courant voltaique," Annates de chimie et de physique, 1820, vol. 15, pp. 93-102. ™ A. M. Ampere, "Suite du memoire sur Taction mutuelle entre deux courants electriques, entre un courant electrique et un aiman ou le globe terrestre, et entre deux aimans," Annates de chimie et de physique, 1820, vol. 15, pp. 170-218. ™ "Papers in Chemistry, No. 3: Improved Electro-Magnetic Apparatus," Transactions of the Society for the Encouragement of Arts, Manufactures, and Commerce, 1824, vol. 43, pp. 37—52. i § ^^ Wi ^m 1 1 1. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appear
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