38 WRITINGS OP JOSEPH HENRY. [1831 



pere, to shew the action of terrestrial magnetism on a gal- 

 vanic current, instead of using a short single wire suspended 

 on steel points ; 60 feet of wire, covered with silk, are coiled 

 so as to form a ring of about 20 inches in diameter, the sev- 

 eral strands of which are bound together by wrapping a 

 narrow silk ribbon around them. The copper and zinc of 

 a pair of small galvanic plates are attached to the ends of 

 the coil, and the whole suspended by a silk fibre, with the 

 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 meri4ian. This article 

 is nothing more than a modification of De la Rive's ring on 

 a larger scale. 



Shortly after the publication mentioned, several other ap- 

 plications 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 application to a devel- 

 opement of magnetism in soft iron, much more extensively, 

 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, cov- 

 ered 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 became much more powerfully magnetic, 

 than another of the same size, and wound in the usual 

 manner, by the application of a battery composed of 28 

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

 convenient form of this apparatus was contrived, by wind- 

 ing a straight bar of iron 9 inches long with 35 feet of wire, 

 and supporting it horizontally 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, 



