CHAP. II.] ELECTRICITY AND MAGNETISM. 75 



pole, and that the S.-pointing pole repels the S.-pointing 

 pole ; but that a N.-pointing pole attracts and is attracted 

 by a S.-pointing pole. 



81. Two kinds of Magnetic Poles. There would 

 therefore appear to be two opposite kinds of magnetism, 

 or at any rate two opposite kinds of magnetic poles, 

 which attract or repel one another in very much the 

 same fashion as the two opposite kinds of electricity do ; 

 and one of these kinds of magnetism appears to have a 

 tendency to move toward the north and the other to 

 move toward the south. It has been proposed to call 

 these two kinds of magnetism "north-seeking magnet- 

 ism " and " south-seeking magnetism," but for our pur- 

 pose it is sufficient to distinguish between the two kinds 

 of poles. In common parlance the poles of a magnet 

 are called the " North Pole " and " South Pole " respect- 

 ively, and it is usual for the makers of magnets to mark 

 the N.-pointing pole with a letter N. It is therefore 

 sometimes called the " marked " pole, to distinguish it 

 from the S.-pointing or " unmarked " pole, We shall, to 

 avoid any doubt, 1 call that pole of a magnet which 

 would, if the magnet were suspended, tend to turn to the 



1 It is necessary to be precise on this point, as there is some confusion in 

 the existing text-books. The cause of the confusion is this : If the north- 

 pointing pole of a needle is attracted by magnetism residing near the North 

 Pole of the earth, the law of attraction (that -unlike poles attract), shows us 

 that these two poles are really magnetically of opposite kinds. Which are 

 we then to call north magnetism? That which is at the N. pole of the earth? 

 If so, we must say that the N.-pointing pole of the needle contains south 

 magnetism. And if we call that north magnetism which points to the north, 

 then we must suppose the magnetic pole at the north pole of the earth to have 

 south magnetism in it. In either case there is then a difficulty. The Chinese 

 and the French call the N.-pointing pole of the needle a south pole, and the 

 S.-pointing pole a north pole. Sir Wm. Thomson also calls the N.-pointing 

 pole a "True South" pole. But common practice goes the other way, and 

 calls the N.-pointing pole of a magnet its "North" pole. For experimental 

 purposes it is usual to paint the two poles of a magnet of different colours, 

 the N. -seeking pole being coloured red and the S. -seeking pole bine; but 

 here again, strangely enough, authorities differ, for in the collections of 

 apparatus at the Royal Institution and Royal School of Mines, the colours 

 are used in exactly the opposite way to this, which is due to Sir G. Airy. 



