Figure 43. — Henry's quantity electromagnet. 

 From American Journal of Science, 1831, vol. 

 19, p. 408. 



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. 





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Wi 





^m 







1 







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1 





Figure 44. — Henry's "Yale" electromagnet. 

 {USNM i8i243i Smithsonian photo 13346.) 



when excited by a battery with 130 square inches of 

 zinc (fig. 42). G. Moll '^ of the university at Utrecht, 

 made a still larger electromagnet, weighing 26 pounds, 

 that lifted 154 pounds when excited by a battery with 

 1 1 square feet of zinc. 



" Gerard Moll, "Electromagnetic Experiments,'' 

 Journal of Science, 1830, vol. 19, pp. 329-337. 



American 



258 



BULLETIN 228 : CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



