370 FRAGMENTS OF SCIENCE. 



short, you will, in all likelihood, have enriched your expe- 

 rience in many ways without any special direction from 

 me. 



Well, the magnet attracts the nail, and that nail attracts 

 a second one. This proves that the nail in contact with 

 the magnet has had the magnetic quality developed in it 

 by that contact. If it be withdrawn from the magnet, its 

 power to attract its fellow-nail ceases. Contact, however, 

 is not necessary. A sheet of glass or paper, or a space 

 of air, may exist between the magnet and the nail ; the 

 latter is still magnetized, though not so forcibly as when 

 in actual contact. The nail then presented to the magnet 

 is itself a temporary magnet. That end which is turned 

 toward the magnetic pole has the opposite magnetism of 

 the pole which excites it ; the end most remote from the 

 pole has the same magnetism as the pole itself, and be- 

 tween the two poles the nail, like the magnet, possesses a 

 magnetic equator. 



Conversant as you now are with the theory of magnetic 

 fluids, you have already, I doubt not, anticipated me in 

 imagining the exact condition of the iron under the in- 

 fluence of the magnet. You picture the iron as possessing 

 the neutral fluid in abundance, you picture the magnetic 

 pole, when brought near, decomposing the fluid ; repelling 

 the fluid of a like kind with itself, and attracting the unlike 

 fluid ; thus exciting in the parts of the iron nearest to itself 

 the opposite polarity. But the iron is incapable of becoming 

 a permanent magnet. It only shows its virtue as long as 

 the magnet acts upon it. "What, then, does the iron lack 

 which the steel possesses ? It lacks coercive force. Its 

 fluids are separated with ease, but, once the separating 

 cause is removed, they flow together again and neutrality 

 is restored. Your imagination must be quite nimble in 

 picturing these changes. You must be able to see the 

 fluids dividing and reuniting according as the magnet is 



