MAGNETS. 187 



in the same way the other is called the negative fluid. It is imag- 

 ined that each of these two fluids repels its like and attracts its 

 opposite ; that neither can exist without the other, every magnet 

 possessing equal quantities of both ; that, owing to their mutual 

 attraction, they tend to combine in or around each molecule and 

 thus neutralize each other ; that they may be separated by a force 

 greater than their mutual attraction, and made to arrange them- 

 selves in a certain position in or about the molecules to which they 

 belong, but that they cannot be removed from them. In this way 

 we imagine to our minds the formation of a magnet by bringing 

 together rows of polarized molecules, whose similar poles are 



turned in the same direction. 



The magnetic separation thus 

 FIG. 123. imagined is represented in Fig. 



123. The effects of the opposite 



polar fluids neutralize each other at the middle of the bar, but are 

 manifested at opposite ends of the bar. ( 335.) 



309. A Hypothetical Theory. The theory sketched in 

 the preceding paragraph has value because it connects the various 

 phenomena of magnetism. But we must remember that it is only 

 a hypothesis, and is seriously doubted by scientific men. Neither 

 itTnbr its companion, the Theory of Electric Fluids, can be re- 

 ceived unsuspectingly until they can connect the phenomena of 

 magnetism and electricity one with the other, and both of them 

 with the phenomena of heat and light. Although as yet they can- 

 not do this, we may use them with profit unless we allow ourselves 

 to accept them with a confidence that blinds our sight to the 

 approach of something better. 



310. Magnetic and Diamagnetic Substances. Sub- 

 stances that are attracted by a, magnet are called magnetic; e.g., iron 

 or steel and nickel. Substances that are repelled by a magnet are 

 called diamagnetic; e. g , bismuth, antimony, zinc, tin, mercury, 

 lead, silver, copper, gold and arsenic. Of these, iron is by far the 

 most magnetic, while bismuth is the most diamagnetic. The mag- 

 netic properties of iron or steel are easily shown ; diamagnetic 

 properties require a powerful magnet for satisfactory illustration. 



311. Magnetic Induction. If a bar of soft iron 

 be brought near one of the poles of a strong magnet, it 

 becomes, for the time being, a magnet. The poles of the 



