ON MAGNETISM. 687 



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 very 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 aurora borealis is certainly in some measure a 

 raagnetical phenomenon, and if iron were the only substance capaple of 

 exhibiting magnetic effects, it would follow that some ferruginous particles 

 must exist in the upper regions of the atmosphere. The light usually attend- 

 ing this maguetical meteor may possibly be derived from electricity, which 

 may be the immediate cause of a change of the distribution of the magnetic 

 fluid, contained in the ferruginous vapours, that are imagined to float ia 

 the air. 



We arc still less capable of distinguishing with certainty in magnetism, 

 than in electricity, a positive from a negative state, or a real redundancy of 

 the fluid from a deficiency. The north pole of a magnet may be considered 

 as the part in which the magnetic fluid is either redundant or deficient, pro- 

 vided that the south pole be understood in a contrary sense: thus, if the 

 north pole of a magnet be supposed to be positively charged, the south pole 

 must be imagined to be negative; and in hard iron or steel these poles may 

 be considered as unchangeable. 



A north pole, therefore, always repels a north pole, and attracts a south 

 pole. And in a neutral piece of soft iron, near to the north pole of a 

 magnet, the fluid becomes so distributed by induction, as to form a 

 temporary south pole next to the magnet, and the whole piece is of course 

 attracted, from the greater proximity of the attracting pole. If the bar is 

 sufficiently soft, and not too long, the remoter end becomes a north pole, 

 and the whole bar a perfect temporary magnet. But when the bar is of 

 hard steel, the state of induction is imperfect, from the resistance opposed 

 to the motion of the fluid ; hence the attraction is less powerful, and an 

 opposite pole is formed, at a certain distance, within the bar; and beyond 

 this another pole, similar to the first; the alternation being sometimes re- 

 peated more than once. The distribution of the fluid within the magnet is 

 also affected by the neighbourhood of apiece of soft iron, the north pole 



