Electro-Magnetic Experiments. 401 



galvanic-element hanging in a tumbler of diluted acid. 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 applications 

 of the coil, besides those described in that paper, Avere 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 eifected 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, which 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 me, 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 Avire ; with a pair of plates containing only 2|- square inches 

 of zinc, it lifted 14 lbs. avoirdupois. At the same tinie, a veiy mate- 

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

 on reading a more detailed account of Prof. Schweiger's galvanometer, 

 and Avhich 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 

 wire, 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 galvanic 

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

 words, that the two v/ires might act as one; the efi^ect by this addition 

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

 supported 28 lbs. 



