THE MAGNETIC FIELD OF FORCE 



477 



the needle act when it is over the ends of the magnet ? How does 

 the direction of the compass needle compare with the direction of 

 the bar magnet ? 



In the experiment just performed we found that when 

 iron filings were sprinkled above the magnet they arranged 

 themselves in definite lines. The small compass needle also 

 arranged itself along these lines when brought under the 

 influence of the magnet. There 

 is, then, around a magnet a mag- 

 netic field of force which affects 

 magnets and magnetic substances 

 brought within it. It is found 

 that magnetic intensity, like the 

 intensity of sound and light, varies 

 inversely as the square of the 

 distance. 



When the compass was placed 

 above the ends of the bar magnet 

 one of the ends of the needle was 

 pulled down toward the magnet, 

 or it might be said to dip toward 

 the magnet. When moved near 

 the middle of the magnet it as- 

 sumed a horizontal position, and 

 when it approached the opposite end of the magnet the 

 opposite end of the needle dipped. This same action is 

 found when a magnetic needle is carried from north to 

 south upon the earth. If a needle is carefully balanced and 

 then magnetized, it will be found no longer to assume a 

 horizontal position. 



In the northern hemisphere the north end will dip and in 

 the southern hemisphere the south end. In the northern 



FIGURE 149 



