JV 



CHAP, ii.] ELECTRICITY AND MAGNETISM. 1 I 95 



tions and repulsions which apparently act across empty 

 space. 



LESSON XI. Laws of Magnetic Force. 



116. Laws of Magnetic Force. 



FIRST LAW. Like magnetic poles repel one 

 another j ^mlike magnetic poles attract one 

 another. 



SECOND LAW. The force exerted between two 

 magnetic poles is proportional to the product 

 of their strengths, and is inversely propor- 

 tional to the square of the distance between 

 them. 



117. The Law of Inverse Squares. The second 

 of the above laws is commonly known as the law of 

 inverse squares. The similar law of electrical attrac- 

 tion has alread/ been explained and illustrated (Art. 

 1 6). This law furnishes the explanatif&n of a fact men- 

 tioned in an earlier Lesson, Art. 77', that small pieces 

 of iron are drawn bodily up to a magnet pole. If a 

 small piece of iron wire, a b (Fig. 54), be suspended by 

 a thread, and the 



N. -pointing pole 

 A of a magnet be 

 brought near it, 

 the iron is thereby 

 inductively mag- 

 netised ; it turns 



round and points Fl 



towards the mag- 

 net pole, setting itself as nearly as possible along a line 

 of force, its near end b becoming a S. -seeking pole, and 

 its further end a becoming a N.-seeking pole. Now the 

 pole b will be attracted and the pole a will be repelled. 

 But these two forces do not exactly equal one another, 

 since the distances are unequal. The repulsion will 



