ELEMENTARY MAGNETISM. 361 



new position. It is repelled by N, 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 completing the parallelogram mnop, 

 and drawing its diagonal up. Along n p, 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 n q. If we place at n a short magnetic needle, 

 its north pole will be urged along n p, its south pole 

 along n q, the only position possible to the needle, 

 thus acted on, being along the line p q, 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 centres from 

 which the force emanates, we could, in accordance with 

 ordinary mechanical principles, assign a definite direc- 

 tion to the magnetic needle at every particular place. 

 And substituting, 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 ex- 

 periment, moreover, instead of the iron filings, very 

 small scraps of thin iron wire might be employed. I 

 place a sheet of paper over the magnet ; it is all the 

 better if the paper be stretched on a wooden frame, as 

 this enables us to keep it quite level. I scatter the 



