one or two other metals have the same property, but in a very
slight degree. It is also remarkable that, however powerfully a
bar of steel may be magnetized, not the slightest effect of the
magnetism can be seen by its action on other than magnetic
substances. It is no heavier than before. Its magnetism does not
produce the slightest influence upon the human body. No one would
know that it was magnetic until something containing iron was
brought into its immediate neighborhood; then the attraction is
set up. The most important principle of magnetic science is that
there are two opposite kinds of magnetism, which are, in a certain
sense, contrary in their manifestations. The difference is seen in
the behavior of the magnet itself. One particular end points
north, and the other end south. What is it that distinguishes
these two ends? The answer is that one end has what we call north
magnetism, while the other has south magnetism. Every magnetic bar
has two poles, one near one end, one near the other. The north
pole is drawn towards the north pole of the earth, the south pole
towards the south pole, and thus it is that the direction of the
magnet is determined. Now, when we bring two magnets near each
other we find another curious phenomenon. If the two like poles
are brought together, they do not attract but repel each other.
But the two opposite poles attract each other. The attraction and
repulsion are exactly equal under the same conditions. There is no
more attraction than repulsion. If we seal one magnet up in a
paper or a box, and then suspend another over the box, the north
pole of the one outside will tend to the south pole of the one in
the box, and vice versa.

Our next discovery is, that whenever a magnet attracts a piece of
iron it makes that iron into a magnet, at least for the time