and on the Theory of Magnetism. 75 



the zinc to the copper, it will be in each connected pair 

 of plates from the copper to the zinc; and the wire I have 

 used is that connection between the two plates of one pair. In 

 the diagrams I may have occasion to subjoin the ends of 

 the connecting wire, marked Z and- C, are connected with the 

 zinc and copper-plates respectively ; the sections are all hori- 

 zontal and seen from above, and the arrow-heads have been 

 used sometimes to mark the pole of a needle or magnet which 

 points to the north, and sometimes to mark the direction of 

 motion ; no difficulty can occur in ascertaining to which of those 

 uses any particular head is applied. 



On placing the wire perpendicularly, and bringing a needle 

 towards it to ascertain the attractive and repulsive positions 

 with regard to the wire ; instead of finding these to be four, one 

 attractive and one repulsive, for each pole, I found them to be 

 eight, two attractive and two repulsive for each pole : thus 

 allowing the needle to take its natural position across the wire, 

 which is exactly opposite to that pointed out by Oersted for 

 the reason before-mentioned, and then drawing the support 

 away from the wire slowly, so as to bring the north pole, for 

 instance, nearer to it, there is attraction, as is to be expected ; 

 but on continuing to make the end of the needle come nearer 

 to the wire, repulsion takes place, though the wire still be on 

 the same side of the needle. If the wire be on the other side 

 of the same pole of the needle, it will repel it when opposite 

 to most parts between the centre of motion and the end ; but 

 there is a small portion at the end where it attracts it. Fig. 1 , 

 plate iii, shews the positions of attraction for the north and 

 south poles, fig. 2, the positions of repulsion. 



If the wire be made to approach perpendicularly towards one 

 pole of the needle, the pole will pass off on one side, in that 

 (lirection which the attraction and repulsion at the extreme 

 point of the pole would give ; but, if the wire be continually 

 made to approach the centre of motion, by either the one or 

 other side of the needle, the tendency to move in the former 

 direction diminishes ; it then becomes null, and the needle 

 is quite indifferent to the wire ; and ultimately the motion is 



