MAGNETIC EFFECTS OF ELECTRIC CURRENTS 225 



approximately north and south. For convenience we call 

 the north end the north pole (JV), and the south end the 

 south pole (). It can easily be shown that like poles of 

 different magnets (two N poles or two 8 poles) repel each 

 other and that two unlike poles attract each other. 



A compass (fig. 112) can be made by magnetizing a steel 

 needle, a safety-razor blade, a small file, or a piece of watch 



FIG. 112. Demonstration materials for studying permanent magnets 



The materials suspended from the rod are three bar magnets to which nails and 

 cobalt and nickel cubes adhere ; a horizontal bar magnet with nails adhering at 

 both ends, the whole acting as a compass ; two U-magnets with nails, one holding 

 the nails though separated from them by cardboard ; a U-magnet holding a nail 

 and piece of wire ; two types of compasses 



spring. When placed on a floating cork or balanced on a 

 pivot the magnet takes a definite north-arid-south direction. 

 This action of the compass is due to the influence of the 

 earth, which acts as though it were a magnet, having a south 

 magnetic pole near the geographical north pole of the earth, 

 and a north magnetic pole near the south pole. The compass 

 needle does not point north and south on all parts of the 

 earth, because the magnetic poles do not coincide exactly with 

 the geographical poles. The compass is used by hunters, 

 sailors, and explorers to determine the directions. 



