76 ELEMENTARY LESSONS ON [CHAP. n. 



north, the " North -seeking" pole, and the other the 

 " South-seeking " pole. 



We may therefore sum up our observations in the 

 concise statement : Like magnetic poles repel one another; 

 unlike poles attract one another. This we may call the 

 first law of magnetism. 



82. The two Poles inseparable. It is impossible 

 to obtain a magnet with only one pole. If we magnetise 

 a piece of steel wire, or watch spring, by rubbing it with 

 one pole of a magnet, we shall find that still it has two 

 poles one N.-seeking, the other S.-seeking. And if we 

 break it into two parts, each part will still have two 

 poles of opposite kinds. 



83. Magnetic Force. The force with which a 

 magnet attracts or repels another magnet, or any piece 

 of iron or steel, we shall call magnetic forced The 

 force exerted by a magnet upon a bit of iron or on another 

 magnet is not the same at all distances, the force being 

 greater when the magnet is nearer, and less when the 

 magnet is farther off. In fact the attraction due to a 

 magnet-pole falls off inversely as the square of the 

 distance from the pole. (See Art. 117.) 



Whenever a force acts thus between two bodies, it acts 

 on both of them, tending to move both. A magnet will 

 attract a piece of iron, and a piece of iron will attract a 

 magnet. This was shown by 

 Sir Isaac Newton, who fixed a 

 magnet upon a piece of cork and 

 floated it in a basin of water 

 (Fig. 44), and found that it moved 

 "^ across the basin when a piece of 

 Flg> 44 ' iron was held near. A compass 



needle thus floated turns round and points north and 

 south ; but it does not rush towards the north as a 

 whole, nor towards the south. The reason of this will 

 be explained later, in Art. 117. 



1 See footnote on " Force," Art. 155. 



