352 ANALOGY OF MAGNETISM AND ELECTRICITY. [SECT. xxx. 



decomposition of the united fluids is accomplished by the 

 inductive influence of either of the separate fluids ; that is to 

 say, a ferruginous body acquires polarity by the approach of 

 either the south or north pole of the magnet. The magnetic 

 fluids pervade each molecule of the mass of bodies, and in all 

 probability the electric fluid does the same, though it appears 

 to be confined to the surface ; if so, a compensation must take 

 place among the internal forces. The electric fluid has a 

 perpetual tendency to escape, and does escape, when not 

 prevented by the coercive power of the surrounding air and 

 other non-conducting bodies. Such a tendency does not 

 exist in the magnetic fluids, -which never quit the substance 

 that contains them under any circumstances whatever ; nor 

 is any sensible quantity of either kind of polarity ever trans- 

 ferred from one part to another of the same piece of steel. 

 It appears that the two magnetic fluids, when decomposed 

 by the influence of magnetising forces, only undergo a dis- 

 placement to an insensible degree within the body. The 

 action of all the particles so displaced upon a particle of 

 the magnetic fluid in any particular situation, compose a 

 resultant force, the intensity and direction of which it is the 

 province of the analyst to determine. In this manner M. 

 Poisson has proved that the result of the action of all the 

 magnetic elements of a magnetised body, is a force equi- 

 valent to the action of a very thin stratum covering the 

 whole surface of a body, and consisting of the two fluids 

 the austral and the boreal, occupying different parts of it ; 

 in other words, the attractions and repulsions externally 

 exerted by a magnet are exactly the same as if they pro- 

 ceeded from a very thin stratum of each fluid occupying 

 the surface only, both fluids being in equal quantities, and 

 so distributed that their total action upon all the points in 

 the interior of the body are equal to nothing. Since the 

 resulting force is the difference of the two polarities, its 

 intensity must be greatly inferior to that of either. 



In addition to the forces already mentioned, there must 



