CHAPTER XXII 



ELECTRICAL MACHINERY 



601. Natural magnets. The name magnet was given 

 by the ancients to a brown-colored stone which had the 

 property of attracting certain metals. Later the Chinese 

 found that when free to move this stone always pointed 

 in one direction, and they named it loadstone (meaning 

 to lead). The commercial name for it is magnetite 

 (Fe 3 O 4 ). This mineral is found in such quantities in sev- 

 eral localities that it is a valuable ore for producing iron. 



FIG. 339 NATURAL AND ARTIFICIAL MAGNETS ATTRACTING IRON FILINGS 



602. Artificial magnets. - - The ancients learned by 

 stroking pieces of steel with natural magnets that the 

 steel would become magnetized. Magnets produced 

 in this manner are known- as artificial. They are now 

 made by stroking bars of steel with another magnet or 

 an electromagnet, which will be described later. 



603. Poles. If a magnet is sprinkled with tacks or iron 

 filings, it will be noticed that the filings attach them- 

 selves to the ends of the magnet but not to the middle of 

 it. The name poles has been given to these places where 

 the filings adhere. A suspended. magnet will swing so 

 that one of its poles points toward the north. This pole 

 is then known as the + or north-seeking pole, or simply 

 the north pole (N), and the other end is known as the 



