He reaches his haven only after many spells of 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.
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