SECT, xxx.] BAEON POISSON's HYPOTHESIS. 351 



tances a law that is not affected by the intervention of 

 any substance whatever between the magnet and the needle, 

 provided that substance be not itself susceptible of mag- 

 netism. Induction and the reciprocal action of magnets 

 are therefore subject to the laws of mechanics ; but the com- 

 position and resolution of the forces are complicated, in 

 consequence of four forces being constantly in activity, two 

 in each magnet. 



Mr. Were Fox, who has paid much attention to this branch 

 of the science, has lately discovered that the law of the mag- 

 netic force changes from the inverse squares of the distances 

 to the simple inverse ratio, when the distance between two 

 magnets is as small as from the fourth to the eighth of an 

 inch, or even as much as half an inch when the magnets are 

 large. He found that, in the case of repulsion, the change 

 takes place at a still greater distance, especially when the two 

 magnets differ materially in intensity. 



There can hardly be a doubt but that all the phenomena 

 of magnetism, like those of electricity, may be explained on 

 the hypothesis of one ethereal fluid, which is condensed or 

 redundant in the positive pole, and deficient in the negative ; 

 a theory that accords best with the simplicity and general 

 nature of the laws of creation ; nevertheless, Baron Poisson 

 has adopted the hypothesis of two extremely rare fluids per- 

 vading all the particles of iron, and incapable of leaving 

 them. Whether the particles of these fluids are coincident 

 with the molecules of the iron, or that they only fill the 

 interstices between them, is unknown and immaterial. But 

 it is certain that the sum of all the magnetic molecules, added 

 to the sum of all the spaces between them, whether occupied 

 by matter or not, must be equal to the whole volume of the 

 magnetic body. When the two fluids in question are com- 

 bined, they are inert, so that the substances containing them 

 show no signs of magnetism; but, when separate, they are 

 active, the molecules of each of the fluids attracting those of 

 the opposite kind, and repelling those of the same kind. The 



