WHAT CAN MAGNETS DO? 171 



The magnetic field around a bar magnet. 



coming out of the north pole, circling around, and enter- 

 ing the south pole of the magnet. The magnetic field is 

 seen clearly in the illustration above. 



The Earth as a Magnet. If you had a magnet mounted 

 on a horizontal axis and you traveled with it from New 

 York over Canada toward Hudson Bay, you would find 

 that the compass needle pointed a little west of north, and, 

 as you went farther north, it would dip more and more 

 toward the perpendicular. If you were explorers, you would 

 find a place north of Hudson Bay where the compass would 

 point down toward the center of the earth. This is the 

 magnetic pole in our northern hemisphere. A similar 

 magnetic pole exists in the southern hemisphere. These 

 magnetic poles are each a good many hundred miles away 

 from the geographic pole where the earth rotates on its 

 axis. The earth, being a magnet, is surrounded by mag- 

 netic lines of force. It is because of these lines of force 

 that the compass acts as it does. 



Value of the Compass. We only have to think of the 

 pilot on sailing vessels or steamers shut in by a dense fog, 

 or of aviators flying blind, to realize the great value of 

 the compass in modern life. For many years the great 

 steamships depended largely upon the magnetic compass. 



