WHAT MAKES THE TROLLEY CAR GO. 



317 



difficult, if not impossible, to obtain one without the other, although 

 it is a simple matter to make one inactive under certain conditions. 

 It is very generally understood that a magnet possesses the power 

 of attraction, and that it will draw toward it pieces of iron, steel, 

 and other magnets. The laws governing the attractive properties 

 of magnets, however, are not so well understood, and many are 

 not aware of the fact that under certain conditions one magnet 

 will repel another, but such is nevertheless the case. 



In Fig. 1 the lower outline, M, represents a magnet fixed in 

 position, and the upper bar represents another magnet arranged 

 to swing freely around the pivot a. A magnet, as is generally 

 known, will arrange itself in a north-to-south position if suspended 

 from its center, like a scale beam, and allowed to swing freely, and 

 the same end will always point toward the north. On this account 

 the ends of a magnet are called its poles, and the one that will 

 point toward the north is desig- 

 nated the north pole, while the 

 other one is the south pole. The 

 terms north and south poles were 

 applied to magnets centuries ago, 

 but at the present time the ends 

 are more commonly designated 

 as positive and negative. In Fig. 

 1 it will be noticed that the sta- 

 tionary magnet has its positive 

 end upward, and this attracts the 

 negative end of the swinging 

 magnet. If the order of the 



poles is reversed, so that the positive of the swinging magnet wdll 

 come opposite the positive of the stationary one, then there will 

 be a repulsive action instead of an attraction, as is shown in Fig. 2. 

 If the two negative ends were placed opposite, the effect would 

 be the same. From this we see that to obtain an attraction we 

 must place the magnets so that opposite poles come together, and 

 that by reversing the order we obtain a repulsive action. 



If the swinging magnet is replaced by a bar of iron, as is shown 

 in Fig. 3, there will be an attraction, no matter what end of the 

 magnet may be uppermost, thus showing that either end of a mag- 

 net will attract a bar of iron. The explanation of these different 

 actions is that when tw'o magnets are brought into proximity to 

 each other each one exerts its force without any regard to the 

 other, and if the two are set to act together they will attract one 

 another, but if set to act in opposition they will repel. When one 

 of the bars is not a magnet, but simply a piece of iron or steel, 



Figs. 1, 2, 3. — Diagrams illustrating the 

 Attraction and Kepllsion of Magnets. 



