Magnetism and Electricity 195 



in the same direction it is almost like combing tangled 

 hair to stroke a needle over a magnet. Then the mole- 

 cules are arranged more as shown in Figure 108. When 

 all the molecules, each of which is a tiny magnet, pull 

 in the same direction, they make a strong magnet, and 

 they magnetize any iron that comes near them just as 

 they were magnetized. 



Steel will stay magnetized a long time ; but ordinary 

 soft iron loses magnetism almost as soon as another 

 magnet is taken away from it, the molecules become 

 all disarranged again. 



In a later section you will find that whenever elec- 

 tricity flows through a wire that is coiled around a piece 

 of iron, the iron becomes magnetized just as when it 

 is rubbed with a magnet. 



Application 47. An explorer lost his compass. In clear 

 weather he could tell the directions by the sun and stars, 

 but in cloudy weather he was badly handicapped. He had 

 with him a gun, plenty of ammunition, a sewing kit, a hunt- 

 ing knife, and some provisions. How could he have made 

 a compass? 



Inference Exercise 

 Explain the following : 



281. Snow turns to water in the first warm weather. 



282. A person's face looks ghastly by the greenish light of a mer- 



cury-vapor lamp. 



283. If a red-hot coal is touched with a cold poker, the coal turns 



black at the place touched. 



284. Stereopticon slides are put in upside down, yet the picture 



on the screen is right side up. 



285. If the vocal cords of your throat did not vibrate, you could 



not talk out loud. 



286. A watch is sometimes put out of order if it is held near a 



magnet. 



