CHAPTER XV 

 MAGNETISM AND ELECTRICITY 



196. Nature of Magnetism. When we take a lump of 

 lodestone, which is an iron ore, and place it near a piece of 

 iron, the lodestone will attract the iron. The iron in its 

 turn will then attract particles of iron. The iron is called 

 an artificial magnet. Thus iron and steel when brought in 

 contact with the lodestone have the property of becoming 

 magnetized and attracting iron. Magnets made of soft iron 

 lose their magnetism very easily and are called temporary 

 magnets; while hard iron and steel retain their magnetism 

 and are called permanent magnets. 



197. Shapes of Magnets. Magnets are of two shapes: 

 straight or bar (Fig. 68) and ^ 



horseshoe (Fig. 69). In every 



magnet there is a FIG. 68. Bar Magnet with 

 limited space sur- Iron Filings ' 



rounding each end or pole in which .its mag- 

 netic properties are exhibited. This is called 

 the magnetic field. If, for example, magnet- 

 ized iron filings are sprinkled over a sheet of 



paper, they will assume curved lines, bring- 

 FIG. 69 .Horse- . ., . , 



shoe Magnet ln g mto view a * ew t what are called the lines 

 with Iron Fil- O f f orce O f a magnetic field. The portion of 

 this magnetic field that is the strongest 

 is assumed to contain the greatest number of lines of force 



167 



