152 ELECTRICITY 



The ends of a magnet, or the points where its mag- 

 netic force seems greatest, are called its poles. In any 

 magnet the two poles act differently toward other mag- 

 netized bodies, so they are separately named: one is 

 called the positive (-[-) or north pole, and the other 

 the negative () or south pole. Permanent magnets are 

 usually marked by a line or groove across the positive 

 pole ; or the positive pole may be marked N and the 

 negative S. 



It must be noted that the steel or iron body is mag- 

 netized not only at its poles but throughout the body ; 

 the poles are simply the parts where the magnetic force 

 acts with the greatest intensity. To show this more 

 clearly, magnetize a steel needle, dip it in iron filings, 

 and note its middle part. Now break it in the middle, 

 dip one part in the filings, and note the end that was a 

 portion of the middle before you broke it. 



176. Law of Magnets. Both poles of a magnet will 

 attract a piece of iron that is not magnetized. Toward 

 a magnetized body, however, the two poles act in an 

 opposite manner. 



Experiment 105. The positive pole of a compass needle is the 

 one that points northward. Secure a bar magnet whose poles are 

 marked. Bring the positive pole of the bar near the + pole of the 

 needle ; note what happens. Now bring the same ( + ) pole of 

 the bar near the negative end of the needle, while it is at rest, 

 and make a note of the result here. Again, present the negative 

 pole of the magnet to the negative end of the needle, noting this 

 result. Finally bring the negative end of the bar to the positive 

 pole of the compass needle, and observe. 



What poles seem to attract each other,,and what poles repel? 

 Sum up your results in a statement of how the poles act. 



