MAGNETISM 153 



Similar experiments with magnets give the same 

 results. The facts may be stated briefly in a Law of 

 Magnets as follows : Like poles repel, and unlike poles 

 attract, each other. 



177. Magnetism of the Earth. A magnetized needle 

 suspended so as to swing in a vertical plane (" up and 

 down ") is called a dipping needle. Fig. Ill shows five 

 different positions of a dipping needle placed on a bar 

 magnet. Note 



that at the nega- 

 tive pole of the 

 bar the positive 

 end of the needle FlG ' m 



is down ; note its other positions with care, and if pos- 

 sible perform the experiment for yourself. 



Now it has been found that a dipping needle carried 

 north or south along any meridian of the earth behaves 

 in much the same way. This and other occurrences 

 show that the earth is a great magnet, having its positive 

 and negative poles like any magnetized body. These 

 magnetic poles are two points on its surface, toward 

 which the compass needle points. The negative mag- 

 netic pole is northwest of Hudson Bay, about 20 south 

 of the north pole. Straight through the earth from this 

 point, at a spot in the Antarctic Ocean about 20 north 

 of the south pole, is the positive magnetic pole. 



178. The Compass. A magnetized strip of steel, 

 finely balanced on a point so that it turns freely, will 

 be so acted upon by the earth's magnetism that its 

 positive pole will point toward the negative (northerly) 



