the Lines of Magnetic Force. 407 



lines of magnetic force and of electric force agree. Results of 

 this kind are well shown in some recent experiments on the effect 

 of iron, when passing by a copper wire in the magnetic field of 

 a horseshoe magnet (3129. 3130.), and also by the action of 

 iron and magnets on each other (3218. 3223.). 



3.256. It is evident, I think, that the experimental data are 

 as yet insufficient for a full comparison of the various lines of 

 power. They do not enable us to conclude, with much assu- 

 rance, whether the magnetic lines of force are analogous to those 

 of gravitation, or direct actions at a distance ; or whether, having 

 a physical existence, they are more like in their nature to those 

 of electric induction or the electric current. I incline at present 

 to the latter view more than to the former, and will proceed to 

 certain considerations bearing on the question, with a view to 

 the further and future elucidation of the subject. 



3257. I think I have understood that the mathematical ex- 

 pression of the laws of magnetic action at a distance is the same 

 as that of the laws of static electric actions ; and it has been 

 assumed at times that the supposition of north and south mag- 

 netisms, spread over the poles or respective ends of a magnet, 

 would account for all its external actions on other magnets or 

 bodies. In either the static or dynamic view, or in any other 

 like them, the exertion of the magnetic forces outwards, at the 

 poles or ends of the magnet, must be an essential condition. 

 Then, with a given bar-magnet, can these forces exist without a 

 mutual relation of the two, or else a relation to contrary mag- 

 netic forces of equal amount originating in other sources ? I 

 do not believe they can ; because, as I have shown in recent 

 researches, the sum of the lines of force are equal for any sec- 

 tion across them taken anywhere externally between the poles 

 (3109.). Besides that, there are many other experimental facts 

 which show the relation and connexion of the forces at one pole 

 to those at the other*; and there is also the analogy with static 

 electrical induction, where the one electricity cannot exist without 

 relation to, equality with, and dependence on the other. Every 

 dual power appears subject to this law as a law of necessity. If 

 the opposite magnetic forces could be independent of each other, 

 I hen ii is evident that a charge with one magnetism only is pos- 

 sible ; but such a possibility is negatived by every known expe- 

 riment and fact. 



* The manner in which a large powerful magnet deranges, overpowers, 

 and even inverts tlic magnetism of a smaller magnet, when it is brought 

 near it in different directions without touching it, presents a number of such 

 cases. 



