MAGNETISM. 55 



inrora borealis is certainly in some measure a magnetical phenome- 

 non, and if iron were the only substance capable of exhibiting 

 maguetical effects, it would follow that some ferruginous particles 

 must exist in the upper regions of the atmosphere. The light 

 usually attending this magnetical 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 in the air. 



We are 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 mag. 

 netic fluid is either redundant or deficient, provided that the south 

 pole be understood hi 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 great 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 some- 

 times repeated more than once. The distribution of the fluid within 

 the magnet is also affected by the neighbourhood of a piece of soft 

 iron, the north pole becoming more powerful by the vicinity of the 

 new south pole, and the south pole being consequently strengthened 

 in a certain degree ; so that the attractive power of the whole mag- 

 net is increased by the proximity of the iron. A weak magnet is 

 capable of receiving a temporary induction of a contrary magnetism, 

 from the action of a more powerful one, its north pole becoming a 

 south pole on tite approach of a stronger north pole; but the original 

 south pole still retains its situation at the opposite end, aud restore* 



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