CHAPTER XIV 



MAGNETISM 



For centuries man knew that bars of a certain metallic 

 ore had the power to attract iron, and that if suspended 

 they would tend to point north and south. Only with the 

 invention of the compass, however, was this knowledge 

 made to serve man. Previously ship captains clung to the 

 coast lines whenever possible, lest they lose their sense of 

 direction. The compass made it safe to travel out of sight 

 of land on long voyages. So the discovery of new con- 

 tinents was made possible. 



Today the compass still directs the ocean commerce of 

 the world, keeps airplanes on their courses, and guides 

 travelers in safety over deserts and through forests. It 

 has saved countless lives on land and sea. 



That the compass serves us at all is due to the fact 

 that its needle moves in response to the mysterious force 

 of the world's greatest magnet the earth itself. 



In various parts of the earth there exists an iron ore lode- 

 stone which has the power of attracting bits of steel and small 

 pieces of iron. Owing to the fact that this ore was common in 

 Magnesia, a province in southern Asia, it was called magnetite. 

 Pieces of lodestone are natural magnets. 



It is an interesting fact that a pocket knife blade, or other 

 piece of steel, when rubbed on a natural magnet, becomes magnetic 

 and remains so for a long time. Such a knife blade or piece of 

 steel is called an artificial magnet. A piece of soft iron also may 

 be magnetized but it retains this property for only a short time. 



Properties of a Magnet. Both natural and artificial magnets 

 possess several special properties, among which are polarity, 

 power to attract iron not magnetized, power to attract and repel 

 magnetic iron, and power to give magnetism to other pieces of 

 iron. These all show that magnetism must be a form of energy, 

 as it tends to produce motion. 



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