MAGNETISM AND ELECTRICITY 



189 



tube with a magnet. The tube of filings will now act as a 

 single magnet. If the tube is shaken, the magnetism is lost. 



I Sy W ^ -v -w N^ ^ ^ I 



FIG. 156. When the molecules of a bar magnet are disarranged, 

 the bar loses its magnetism. 



These experiments lead to the conclusion that at all 

 times every molecule in a piece of iron or steel is a magnet, 

 but that the bar as a whole becomes a magnet only when 



FIG. 157. The Earth's Agonic and Isogonic Lines. 

 Heavy black lines are agonic lines ; light black, isogonic lines. 



