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Electro- Magnetic Experiments. 401 



galvanic-element hanging in a tumbler of diluted arid- After a few 

 oscillations, the apparatus never fails to place itself at right angles to 

 the magnetic meridian. This article is nothing more than a modifica- 

 tion of De la Rive's ring on a larger scale. 



Shortly after the publication mentioned, several other application* 

 of the coil, besides those described in that paper, were made in order 

 to increase the size of electro-magnetic apparatus, and to diminish the 

 necessary galvanic power. The most interesting of these, was its ap- 

 plication to a developement of magnetism in soft iron, much more ex- 

 tensively, than to my knowledge had been previously effected by a 

 small galvanic element. 



A round piece of iron, about } of an inch in diameter, was bent into 

 the usual form of a horse-shoe, and instead of loosely coiling around 

 it a few feet of wire, as is usually described, it was tightly wound with 

 35 feet of wire, covered with silk, so as to form about 400 turns : a 

 pair of small galvanic plates, which could be dipped into a tumbler of 

 diluted acid, was soldered to the ends of the wire, and the whole 

 mounted on a stand. With these small plates, the horse-shoe be- 

 came much more powerfully magnetic, than another of the same size, 

 and wound in the usual manner, by the application of a battery com- 

 posed of 28 plates of copper and zinc, each 8 inches square. Another 

 convenient form of this apparatus was contrived, by winding a straight 

 bar of iron 9 inches long with 35 feet of wire, and supporting it hori- 



zontally on a small cup of copper containing a cylinder of zinc, when 

 this cup, w r hich served the double purpose of a stand and the galvanic 

 element, was filled with dilute acid, the bar became a portable 

 electro-magnetic magnet. These articles were exhibited to the Insti- 

 tute in March, 1829. 



The idea afterwards occurred to mc, that a sufficient quantity of gal- 



vanism was furnished by the two small plates, to develope, by means of 

 the coil, a much greater magnetic power in a larger piece of iron. To 

 test this, a cylindrical bar of iron, § an inch in diameter, and about 10 

 inches long, was bent into the form of a horse-shoe, and wound with 

 30 feet of wire ; with a pair of plates containing only 2£ square inch* i 

 of zinc, it lifted 14 lbs. avoirdupois. At the same time, a very mate- 

 rial improvement in the formation of the coil suggested itself to me, 

 on reading a more detailed account of Prof. Schweigers galvanometer, 

 and which was also tested with complete success upon the same 

 horse-shoe : it consisted in using several strands of wire, each cover- 



ed with silk, instead of one :— agreeably to this construction, a second 

 ^'ire, of the same length as the first, was wound over it, and the ends 

 soldered to the zinc and copper in such a manner that the tlvanic 

 current might circulate in the same direction in both, or, in other 

 Words, that the two wires might act as one; the effect by this addition 

 was doubled, as the horse-shoe, with the same plates before used, now 

 supported 2- lbs. 



