54 MAGNETISM. 



Provost, appear to be too complicated, and too little supported by 

 facts, to require much of our attention. 



The distinction between conductors and nonconductors is, with re. 

 spect to the electric fluid, irregular and intricate; but in magnetism 

 the softness or hardness of the iron or steel constitutes the only 

 difference. Heat, as softening iron, must consequently render it 

 a conductor ; even the heat of boiling water affects it, in a certain 

 degree, although it can scarcely be supposed to alter its temper; but 

 the effect of a moderate heat is not so considerable in magnetism 

 as in electricity. A strong degree of heat appears, from the expe- 

 riments of Gilbert, and of Mr. Cavallo, to destroy completely all 

 magnetic action. 



It is perfectly certain that magnetic effects are produced by quan- 

 tities of iron incapable of being detected either by their weight or by 

 any chemical tests. Mr. Cavallo found that a few particles of steel, 

 adhering to a hone, on which the point of a needle was slightly 

 rubbed, imparted to it magnetic properties ; and Mr. Coulomb has 

 observed, that there are scarcely any bodies in nature which do not 

 exhibit some marks of being subjected to the influence of mag. 

 netism, although its force is always proportional to the quantity of iron 

 which they contain, as far as that quantity can be ascertained; a single 

 grain being sufficient to make 20 pounds of another metal sensibly 

 magnetic. A combination, with a large proportion of oxygen, de- 

 prives iron of the whole or the greater part of its magnetic proper, 

 ties ; finery cinder is still considerably magnetic, but the more per. 

 feet oxids and the salts of iron only in a slight degree ; it is also 

 said thai antimony renders iron incapable of being attracted by 

 the magnet. Nickel, when freed from arsenic and from cobalt, is 

 decidedly magnetic, and the more so as it contains less iron. Some 

 of the older chemists supposed nickel to be a compound metal con- 

 taining iron ; and we may still venture to assume this opinion as a 

 magnetical hypothesis. There is indeed no way of demonstrating 

 that it is impossible for two substances to be so united as to be 

 incapable of separation by the art of the chemist; had nickel been 

 as dense as platina, or as light as cork, we could not have supposed 

 that it contained any considerable quantity of iron, but in fact the 

 specific gravity of these metals is rery nearly the same, and nickel is 

 never found in nature but in the neighbourhood of iron ; we may 

 therefore suspect, with some reason, that the hypothesis of the 

 existence of iron in nickel may be even chemically true. The 



