ELEMENTARY MAGNETISM. 275 



your magnet than to the other; the forces acting on the 

 particle are no longer equal; the nearest pole of the 

 magnet will act more powerfully on the particle than 

 the more distant one. Let s K, fig. 12, be the magnet, 

 and n the particle of north magnetism, in its new posi- 

 tion. It is repelled by sr, and attracted by s. Let the 

 repulsion be represented in magnitude and direction by 

 the line n o, and the attraction by the shorter line n m. 

 The resultant of these two forces will be found by com- 

 pleting the parallelogram m n op, and drawing its diagonal 

 np. Along np, then, a particle of north magnetism 

 would be urged by the simultaneous action of S and N. 

 Substituting a particle of south magnetism for n, the same 

 reasoning would lead to the conclusion that the particle 

 would be urged along nq. If we place at n a short mag- 

 netic needle, its north pole will be urged along n p, its 

 south pole along n q, the only position possible to the 



S 1* 



FIG. 12. 



needle, thus acted on, being along the line^? g, which is no 

 longer parallel to the magnet. Verify this deduction by 

 actual experiment. 



In this way we might go round the entire magnet; and, 

 considering its two poles as two centers from which the 

 force enarnates, we could, in accordance with ordinary 

 mechanical principles, assign a definite direction to the 

 magnetic needle at every particular place. And substitut- 

 ing, as before, a bit of iron wire for the magnetic needle, 

 the positions of both will be the same. 



Now, I think, without further preface, you will be able 

 to comprehend for yourselves, and explain to others, one of 

 the most interesting effects in the whole domain of 

 magnetism. Iron filings you know are particles of iron, 

 irregular in shape, being longer in some directions than in 

 others. For the present experiment, moreover, instead of 



