and OH the Theory of Magnetism. 87 



be conceived to be occupied by a plane, then the centre of that 

 plane is the spot where the powers are most active on the pole, 

 and move it with most force. Now this spot is actually the 

 pole of this magnetic apparatus. It seems to have powers over 

 the circulating pole, making it approach or attracting it on the 

 one side, and making it recede or repelling it on the other, with 

 powers varying as the distance ; but its powers are only ap- 

 parent, for the force is in the ring, and this spot is merely the 

 place where they are most accumulated : and though it seems to 

 have opposite powers, namely, those of attracting and repelling ; 

 yet this is merely a consequence of its situation in the circle, 

 the motion being uniform in its direction, and really and truly 

 impressed on the pole by its motor, the wire. 



At page 81, it was shewn that two or more similar wires put 

 together in a line, acted as one ; the power being, as it were, ac- 

 cumulated towards the extreme wires, by a species of induction 

 taking place among them all : and at the same time was noticed 

 the similar case of a plate of metal connecting the ends of the ap- 

 paratus, its powers being apparently strongest at the edges. 

 If, then, a series of concentric rings be placed one inside the 

 other, they having the electric current sent through them in tlie 

 same direction ; or if, which is the same thing, a flat spiral of 

 silked wire passing from the centre to the circumference be 

 formed, and its ends be in connexion with the battery, fig. 15, 

 then the circle of revolution would still be as in fig. 14, passing 

 through the centre of the rings or spiral, but the power would be 

 very much increased. Such a spiral, when made, beautifully 

 illustrates this fact ; it takes up an enormous quantity of iron 

 filings, which approach to the form of cones, so strong is the 

 action at the centre ; and its action on the needle by the different 

 sides, is efiainently powerful. 



If in place of putting ring within ring, they be placed side 

 by side, so as to form a cylinder, or if a helix be made, 

 then the same kind of neutralization takes place in the inter- 

 mediate wires, and accumulated eftect in the extreme ones, 

 as Ijcfore. The line which the pole would now travel, sup- 

 posing the inner end of the radius to move over th« inner 



