184 Proceedings of the 



lecturer here remarked a striking analogy between induced electri- 

 city and induced magnetism. 



Mr. Ritchie then proceeded to remove false notions which are some- 

 times entertained with regard to the poles of a magnet, as if the whole 

 magnetic influence were concentrated in those points. He shewed 

 that the poles of a magnet were nothing more than those points at 

 which the attraction of one half of the magnet, diminished by the 

 repulsion of the other half, was a maximum. He candidly con- 

 fessed, that there were some facts connected with magnetism, which 

 could not well be accounted for on any theory. If a piece of very 

 hard tempered steel be formed into a magnet, and then broken in 

 the middle, two distinct and perfect magnets will result ; and if each 

 of these be again broken in the middle, four distinct magnets will 

 result, and so on, according to the number of fractures — a fact, 

 which has yet received no satisfactory explanation. 



The lecturer then proceeded to stale, that the natural electricity 

 of steel might be decomposed by a current of common electricity 

 passing at right angles to the needle to be magnetised, and that 

 powerful magnets might be formed by making the electric current 

 circulate about a spiral of copper wire, having the needle in the axis. 

 By changing the direction of the threads of the spiral, as in the 

 annexed figure, and 



placing a long steel wire in the axis, he shewed that any number of 

 magnets might be formed on the same pieces of steel wire. The 

 annexed figure exhibits the magnets thus connected. 



N SN' S'N'' S" 



For this curious fact we are indebted to M. Arago. He then 

 shewed, by experiment, that magnets might be formed by voltaic 

 electricity even more effectually than by electric discharges. When 

 the discharge from an electric jar is made to circulate round the 

 needle placed on the axis, the north pole is always developed at a 

 certain ending, depending on the direction of the current, and the 

 form of the spiral. When the voltaic influence is made to act in the 

 same manner by means of a single combination of copper and zinc, 

 the north pole is developed as if a current of positive electricity 



