96 



Mr. \V. Sturgeon on Electro-Magnetism. 



attention of every other experimenter, perhaps a detail of 

 those experiments with their Jesuits, and a description of an 

 instrument which I have been led to invent and construct, upon 

 a simple principle, for the purpose of carrying on the compari- 

 son to any required extent, may not be thought uninteresting 

 to some of your readers. 



Exp. 1. I charged in the usual way with dilute nitric 

 acid an Ampere's rotating cylinder, and placed it on a table. 

 I now placed the north pole of a bar magnet on the upper 

 edge of the outer rim of the copper part of that apparatus. 

 I likewise imagined myself " coinciding in position with the 

 wire about which the machine turns," and " looking towards 

 the magnet." On bringing one of the wires of the zinc cylin- 

 der between me and the magnet, that wire was projected to 

 the left. 



Let the line ED, fig. 3, be the hori- jg 



zontal part of the wire in this and the 

 following experiments, moveable on a 

 pivot o ; then, when the wire is said 

 to be projected to the right, it is ?/f Ft J-^ 



meant that the point E is projected 

 towards R, as o R ; and when to the 

 left, the point E is projected towards D 



L, as oh. 



Exp. 2. I now presented the south pole~of the magnet to 

 the wire. The latter was projected to the right. 



Obsei-oation. This chemico-galvanized wire was evidently 

 the ascending wire from the zinc to the copper ; or (which is the 

 same thing) the descending wire from the copper to the zinc. 



Exp. 3. I now suspended by a piece of untwisted silk a 

 semicircular copper wire, with a zinc diameter, as in fig. 4 : 



ccc is a fine copper wire; and zzz a fine slip of zinc, sol- 

 dered to the former at the extremities z z. The north pole 

 of the magnet was now placed close to one arm of the semi- 

 circular arc, as shown in the figure, and the lamp applied at 

 E. The wire was projected to the left. 



Exp. 



