. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PROCEEDINGS OF THE EEGENTS. 101 Mr. Sturgeon, in 1825, made an important step in advance of the experiments of Arago, and produced what is properly known as the electro-magnet. He bent a piece of iron loire into the form of a horse- shoe, covered it with varnish to insulate it, and surrounded it with a helix, of which the spires were at a distance. When a current of galvanism was passed through the helix from a small battery of a single cup
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. PROCEEDINGS OF THE EEGENTS. 101 Mr. Sturgeon, in 1825, made an important step in advance of the experiments of Arago, and produced what is properly known as the electro-magnet. He bent a piece of iron loire into the form of a horse- shoe, covered it with varnish to insulate it, and surrounded it with a helix, of which the spires were at a distance. When a current of galvanism was passed through the helix from a small battery of a single cup the iron wire became magnetic, and continued so during the passage of the current. When the current was interrupted the magnetism disappeared^ and thus was produced the first temporary soft iron magnet. The electro-magnet of Sturgeon is shown , in figure 4, which is an exact copy from the drawing in the Transactions of the Society for the Encouragement of Arts, &c., vol. XLIII. By comparing figures 3 and 4 it will be seen that the helix employed by Sturgeon was of the same kind as that used by Arago; instead, however, of b straight steel wire inclosed in a tube of glass, the former employed a bent wire of soft iron. The difference in the arrangement at first sight might appear to be small, but the difference in the results produced was important, since the temporary magnetism developed in the arrangement of Sturgeon was sufficient to support a weight of several pounds, and an instrument was thus produced of value in future research. The next improvement was made by myself. After reading an account of the galvanometer of Schweigger, the idea occurred to me that a much nearer approximation to the requirements of the theory of Ampere could be attained by insulating the conducting wire itself, instead of the rod to be magnetized, and by covering the whole sur- face of the iron with a series of coils in close contact. This was effected by insulating a long wire with silk t
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