118 Historical Sketch of Electro-magnetism. [Feb. 



ingenious form of apparatus by which these difficulties were 

 overcome. The annexed cut will exhibit one of the 

 modes which he employed to exhibit the motion of a 

 wire round a maonetic pole. Place a portion of mer- 

 cury in a tube closed below by a cork, and fix a small 

 magnet so that one pole shall project above the 

 surface of the mercury. Take a piece of clean 

 copper wire about two inches in length, amalga- 

 mate the two ends, form a loop at one end, and at 

 the end of another piece of wire form another loop, 

 by which hang the first piece ; this affords free 

 motion, and the amalgam allows good contact, fix this 

 over the magnet, so that the end of the moveable 

 piece shall just dip into the mercury ; then connect 

 the mercury with one pole of a voltaic combination, 

 which is readily done through the magnet, and the 

 wire with the other ; and the moveable part will im- 

 mediately revolve round the magnetic pole, and con- 

 tinue to do so as long as the contact is continued. 

 On bringing the magnetic pole from the centre of 

 motion to the side of the wire, there was neither 

 attraction nor repulsion ; but the wire endeavoured to pass off in 

 a circle, still leaving the pole for its centre, and that either on 

 one side or the other according to circumstances. 



All the directions of the motion are reducible to two ; when 

 a current of electricity passes through the wire, the north pole 

 rotates in one direction, and the south in the other. Suppose a 

 watch lying on the table, and let its face be considered as the 

 mercury, and the pivot the north pole of a magnet; a wire 

 dipping into it being negative below, and positive above, would 

 pass round the pole in the direction of the hands of the watch; 

 if the connexion be reversed, or the magnetic pole changed, 

 the motion will be the reverse of the hands. If the wire be 

 made fast, and the pole move round it, the motion is similar, and 

 in the same direction. 



Our limits will not allow us to describe the numerous and 

 highly curious and interesting experiments which Mr. Faraday 

 has made with the poles and wires, having one or more of each, 

 and arranged in different ways. The results of some of these 

 experiments were, that needles, instead of being attracted by 

 their poles, were attracted by their centres. Needles were not 

 attracted merely by the wire, but on arriving at it, still endea- 

 voured to continue their course in the direction in which they 

 had begun it, and on the wire being removed from the one side 

 to the other of them, so as to obviate the mechanical impe- 

 diment it offered, they move on as at first, being apparently 

 repelled : no attraction was observed to exist between a pole 

 and a wire : all these phenomena are referable to the revolving 

 motion. 

 There are some results relating to the theory of M. Ampere which 



