A LECTURE ON MAGNETISM. 373 



middle of the magnet. Of course this is an imaginary case, 

 as you can never in reality thus detach your north mag 

 netism from its neighbor. What is the action of the two 

 poles of the magnet on n ? Your reply will of course be 

 that the pole S attracts n while the pole N repels it. 

 Let the magnitude and direction of the attraction be ex 

 pressed by the line n m, and the magnitude and direction 

 of the repulsion by the line n o. Now the particle n being 

 equally distant from S and N, the line n o, expressing the 

 repulsion, will be equal to m n, which expresses the attrac 

 tion, and the particle n, acted upon by two such forces, 

 must evidently move in the direction p n, exactly midway 

 between m n and n o. Hence you see that, although there 

 is no tendency of the particle n to move toward the mag 

 netic equator, there is a tendency on its part to move 

 parallel to the magnet. If instead of a particle of north 

 magnetism we placed a particle of south magnetism op 

 posite to the magnetic equator, it would evidently be urged 

 along the line n q / and if instead of two separate particles 

 of magnetism we place a little magnetic needle, containing 

 both north and south magnetism, opposite the magnetic 

 equator, its south pole being urged along n q, and its north 

 along n p, the little needle will be compelled to set itself 

 parallel to the magnet S N. Make the experiment, and 

 satisfy yourselves that this is the case. 



Substitute for your magnetic needle a bit of iron wire, 

 devoid of permanent magnetism, and it will set itself ex 

 actly as the needle does. Acted upon by the magnet, the 

 wire, as you know, becomes a magnet and behaves as such ; 

 it will, of course, turn its north pole toward p, and south 

 pole toward q, just like the needle. 



But supposing you shift the position of your particle of 

 north magnetism, and bring it nearer to one end of your 

 magnet than to the other, the forces acting on the particle 

 are no longer equal ; the nearest pole of the magnet will 



