patient
waiting for favoring skies.

The fact that the earth acts like a magnet, that the needle points to
the north, has been generally known to navigators for nearly a thousand
years, and is said to have been known to the Chinese at a yet earlier
period. And yet, to-day, if any professor of physical science is asked
to explain the magnetic property of the earth, he will acknowledge his
inability to do so to his own satisfaction. Happily this does not
hinder us from finding out by what law these forces act, and how they
enable us to navigate the ocean. I therefore hope the reader will be
interested in a short exposition of the very curious and interesting
laws on which the science of magnetism is based, and which are applied
in the use of the compass.

The force known as magnetic, on which the compass depends, is different
from all other natural forces with which we are familiar. It is very
remarkable that iron is the only substance which can become magnetic in
any considerable degree. Nickel and 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 t