OXIDATIONS OF IRON. 333 



be ascribed the conversion of red crayons into magnets, 

 related by H iuy in his elementary Treatise on Natural Phi- 

 losophy; and the magnetic polarity, that displays itself in 

 all the oxides of iron heated before the blowpipe, observed 

 by Mr. Lelievre. 



Besides the weakening of magnetism by division, and That magne* 



. tism must be 



even the complete suspension of its eftects, are consequences wea kened by 



of our theory of magnetism. Though I am not acquainted minute division 

 ' . ' . , X i ' of the substance 



with any accurate experiments, which prove, that magne- deducted from. 



tism acts in the direct ratio of masses, a number of facts the theory. 



attest, that it is subjected to this law*. Every one knows, 



that under similar circumstances a magnet eight inches long 



and an inch thick is more powerful than another of half 



these dimensions. The two hypotheses, that account for 



the magnetism of the earth, rest likewise on this law : for 



it is in consequence of the magnitude of their mass, that 



the action of the magnetic nucleus, or of mines of iron, 



extends to such prodigious distances. Without supposing 



this law, we cannot account for this phenomenon. Thus, 



all other circumstances being equal, a grain of iron will 



have a hundred times the magnetic power of -j-J-^ of a grain, 



a thousand times that of T oW °f a g ra i n > an d so on ; anc * 



the imagination can easily conceive a subdivision, by which 



the magnetic power of a grain of iron would be so divided, 



and its sphere of action so shortened, that the magnetism of 



each particle should not only be unable to pervade the 



space that separates it from another, but even to exhibit 



any signs of magnetism, when brought into contact with a 



magnet. An example will elucidate this. 



Suppose I present the north pole of a needle to a particle This illustrated, 



of iron filings. The austral fluid of this particle will place 



itself at the extremity nearest the needle, while its boreal fluid 



will be expelled to the opposite extremity. But as there is a 



sufficiently appreciable difference between the distance at which 



the north pole of the needle acts on the two fluids of the particle 



of iron, the south energy of this will overcome the north, and 



through this preponderance it will approach the needle. 



* And even though this law should be slightly modified in some 

 way, the effects of this modification would be of little account in 

 the present discussion. 



Z 3 Now 



