Lifting Power of the Electro-Magnet. 293 



electric current and a function of the number and diameters of the spires, but 

 the other is almost totally unknown. It is admitted that these polarities com- 

 port themselves as if they were two fluids, each repelling itself or attracting the 

 other inversely as the square of the distance, and becoming latent when per- 

 mitted to unite ; we might, therefore, suppose that under the influence of the 

 excited helix, they will separate until the increasing repulsion of themselves, 

 and attraction of each other, balance its influence. But there is yet another 

 force which prevents this separation from proceeding quite so far ; it is called 

 the coercive force, and may be described as a resistance which the molecules 

 of iron present to any alteration of their polar condition, whether the change 

 be union or separation of polarities. The first of these will be as the polarity, 

 the last some function of it, of which, I believe, nothing is known. Let now a 

 second section be placed below the first, and in contact with it ; it will be 

 excited to an equal intensity ; but the heteronymous polarities partially neu- 

 tralize each other at the contact surface, and the remaining two being at twice 

 the former distance have less power to oppose the induction of the helix. 

 Therefore it will produce a still greater separation of the polarities, and so on, 

 till the helix is filled with these sections. For this we may evidently substitute 

 a solid bar ; the intervals between its molecules being analogous to the surfaces 

 of contact, and as evidently it can be shown that the extremities of the bar will 

 exhibit opposite polarities, whose intensity gradually decreases towards the 

 centre till it vanishes at that point. If now a keeper of the same section be 

 placed on one extremity of the magnet, suppose the Boreal one, it will also be- 

 come a magnet, and its Austral polarity will neutralize much of the Boreal of 

 the other ; the action of the helix will tlierefore evolve a still higher degree of 

 magnetism in the latter, till a new equilibrium of forces is attained. In this 

 instance, however, we can measure the new polarity, for it is proportional to 

 the force with which the keeper is attracted by the polar extremity of the 

 magnet. On the same principles the development of the magnetism will be 

 carried still higher if the remote extremity of the keeper be connected with the 

 Austral extremity of another magnet ; and it will reach its maximum if the re- 

 maining poles of the two magnets be united as in the ordinary horse-shoe, and 

 thus a magnetic circuit be completed. In this case there woidd be scarcely any 

 free magnetism evident, and the forces which oppose H, the action of the helix 



2 q2 



