ELECTRICITY AS A MAGNET 331 



is brought toward the north pole of the suspended magnet, 

 the latter moves in such a way that the two poles N and N 

 are as far apart as possible. In every case that can be 

 tested, it is found that a north pole repels a north pole, and a 

 south pole repels a south 

 pole; but that a north and 

 a south pole always attract 

 each other. 



The main facts relative to /, 



magnets may be summed up ' |_ 



as follows : N 



a. A magnet points 

 nearly north and south if it 



,, j , . r FlG. 225. A south pole attracts a north pole. 



is allowed to swing freely. 



b. A magnet contains two unlike poles, one of which per- 

 sistently points north, and the other of which as persistently 

 points south, if allowed to swing freely. 



c. Poles of the same name repel each other ; poles of un- 

 like name attract each other. 



d. A magnet possesses the power of attracting certain sub- 

 stances, like iron, and this power of attraction is not limited 

 to the magnet itself but extends into the region around the 

 magnet. 



308. Electricity as a Magnet. If a current of electricity 

 transforms a wire into a real magnet, such a wire must pos- 

 sess all of the characteristics mentioned in the preceding 

 Section. We saw in Section 296 that a coiled wire through 

 which current was flowing would attract iron filings, and that 

 the attraction was practically limited to the two ends of the 

 helix. That a coil through which current flows possesses the 

 characteristics a, b, c, and d, of a magnet is shown as follows : 



a, b. If a helix marked at one end with a red string is 

 arranged so that it is free to rotate and a strong current is 



