UNIT VII 



HOW WE MAY PRODUCE ELECTRICITY 

 AND MAGNETISM 



PREVIEW 



Long before the birth of Christ, it was known that a 

 certain kind of iron ore which came from Magnesia in 

 Asia Minor had the property of attracting other small bits 

 of iron. To this ore, the name of magnetite was given, 

 from which we get our word " magnet." Early peoples 

 called these stones "lodestones" or leading stones, and 

 thought they had magical powers. Although these 

 magical stones were known to the Greeks 600 years before 

 Christ, the Chinese are credited with having made the 

 first practical use of magnets, for they discovered that a 

 lodestone if it floated on a block of wood in water always 

 pointed in a north-south direction. This discovery paved 

 the way for the development of the mariner's compass 

 in Europe in about the eleventh century. Thus it was 

 that the magical lodestone enabled adventurous sailors 

 and explorers like Columbus to sail away out of sight of 

 land to discover new lands. In 1576 it was discovered 

 that a compass needle properly supported would dip 

 toward the poles of the earth unless one were on tne equa- 

 tor. This caused William Gilbert in 1600 to conclude 

 that the earth acts as a great magnet and attracts com- 

 pass needles more strongly in some places than in others. 

 Later still, in 1831, the arctic explorer, Ross, discovered a 

 magnetic pole 1200 miles south of the north pole of the 

 earth. 



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