CHAPTER SEVEN 



MAGNETISM AND ELECTRICITY 



SECTION 31. Magnets; the compass. 



What makes the needle of a compass point north ? 

 What causes the Northern Lights ? 



For many hundreds of years sailors have used the 

 compass to determine directions. During all this time 

 men have known that one point of the needle always 

 swings toward the north if there is no iron near to pull 

 it some other way, but until within the past dentury 

 they did not know why. Now we have found the ex- 

 planation in the fact that the earth is a great big magnet. 

 The experiment which follows will help you to under- 

 stand why the earth's being a magnet should make the 

 compass needle point north and south. 



Experiment 61. Lay a magnetic compass flat on the 

 table. Notice which point swings to the north. Now hold 

 a horseshoe magnet, points down, over the compass. Turn 

 the magnet around and watch the compass needle ; see 

 which end of the magnet attracts the north point; hold 

 that end of it toward the south point and note the effect. 

 Hold the magnet, ends up, under the table directly below 

 the compass and turn the magnet, watching the compass 

 needle. 



The earth is a magnet, and it acts just as your magnet 

 does : one end attracts one point of the compass, and 

 the other end attracts the other point. That ought to 

 make it clear why the compass points north. But how 

 is the compass made? The next experiment will show 

 this plainly. 



Experiment 62. Take a long shoestring and make a 

 loop in one end of it. Slip the magnet through the loop and 



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