202 Electro-Magnet. 



was formed from a bar of Swede's iron three inches square and thir- 

 ty inches long. Before bending the bar into the shape of a horse- 

 shoe, it was flattened on the edges, so as to form an octagonal prism, 

 having a perimeter of 10| inches. The other dimensions of the 

 magnet, as measured before winding it with wire, are as follows : — 

 perpendicular height of the exterior arch of the horse-shoe 1 If inches 

 — around the outside from one pole to the other 29 /„ inches — in- 

 ternal distance between the poles 3J inches. 



The armature or lifter is formed from a piece of iron from the 

 same bar, not flattened on the edges ; it is nearly 3 inches square, 

 9 J inches long, and weighs 23 lbs. The upper surface is made per- 

 fectly flat, except about an inch in the middle where the angles are 

 rounded off" so as to form a groove, into which the upper part of a 

 strong iron stirrup, surrounding the armature, fits somewhat loosely. 

 The weight to be supported is fastened to the lower part of the stir- 

 rup, and by means of the groove is made to bear directly on the cen- 

 ter of the armature. 



For the purpose of suspending the magnet, a piece of round iron 

 with an eye on one end, is firmly screwed into the crown of the arch 

 and is attached to the cross beam of a frame, similar to that figured 

 in the last number of the Journal. 



The magnet is wound with 26 strands of copper bell wire, cover- 

 ed with cotton thread 31 feet long; about 18 inches of the ends are 

 left projecting, so that only 28 feet actually surround the iron ; the 

 aggregate length of the coils is therefore 728 feet. Each strand is 

 wound on a little less than an inch ; in the middle of the horse-shoe 

 it forms three thicknesses of wire, and on the ends or near the poles 

 it is wound so as to form six thicknesses. 



Two small galvanic batteries are soldered to the wires of the mag- 

 net, one on each side of the supporting frame, in such a manner as to 

 cause the poles to be instantaneously reversed, by merely dipping 

 the batteries alternately into acid. To render these as compact as 

 possible, they are formed of concentric copper cylinders with cylin- 

 ders of zinc plates interposed and so united as to form but one gal- 

 vanic pair. Each of these batteries presents to the action of the acid, 

 measuring both surfaces of the plate, 4| square feet — they are 12 

 inches high and about 5 inches in diameter. 



In experimenting with this magnet, a battery containing § of a 

 square foot of zinc surface was first attached to the vi^ires 5 with this 

 the magnet could not be made to support more than 500 lbs. An- 



