272 FRAGMENTS OF SCIENCE. 
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 thus 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 between 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 im- 
agining the exact condition of an iron nail under the influ- 
ence 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 un- 
like 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. Imagination must be quite nimble in picturing 
these changes able to see the fluids dividing and reuniting, 
according as the magnet is brought near or withdrawn. 
Fixing a definite pole in your mind, you must picture the 
precise arrangement of the two fluids with reference to 
this pole, and be able to arouse similar pictures in the minds 
of your pupils. You will cause them to place magnets and 
iron in various positions, and describe the exact magnetic 
state of the iron in each particular case. The mere facts 
of magnetism will have their interest immensely augmented 
by an acquaintance with the principles whereon the facts 
depend. Still, while you use this theory of magnetic fluids 
to track out the phenomena and link them together, you 
will not forget to tell your pupils that it is to be regarded 
as a symbol merely a symbol, moreover, which is incom- 
petent to cover all the facts,* but which does good practU 
*This theory breaks down when applied to diamagnetic bodies 
which are repelled by magnets. Like soft iron, such bodies are 
