_The Laws of Magnetism._
Magnetism has no very obvious or apparently extensive office in
the mechanism of the atmosphere and the earth: but the mention of
it may be introduced, because its ascertained relations to the
other powers which exist in the system are well suited to show us
the connexion subsisting throughout the universe, and to check the
suspicion, if any such should arise, that any law of nature is
without its use. The parts of creation when these uses are most
obscure, are precisely those parts when the laws themselves are
least known.
When indeed we consider the vast service of which magnetism is to
man, by supplying him with that invaluable instrument the mariners’
compass, many persons will require no further evidence of this
property being introduced into the frame of things with a worthy
purpose. As however, we have hitherto excluded _use in the arts_
from our line of argument, we shall not here make an exception in
favour of navigation, and what we shall observe belongs to another
view of the subject.
Magnetism has been discovered in modern times to have so close
a connexion with galvanism, that they may be said to be almost
different aspects of the same agent. All the phenomena which we can
produce with magnets, we can imitate with coils of galvanic wire.
That galvanism exists in the earth, we need no proof. Electricity,
which appears to be only galvanism in equilibrium, is there in
abundance; and recently, Mr. Fox[13] has shown by experiment that
metalliferous veins, as they lie in the earth, exercise a galvanic
influence on each other. Something of this kind might have been
anticipated; for masses of metal in contact, if they differ in
temperature or other circumstances, are known to produce a galvanic
current. Hence we have undoubtedly streams of galvanic influence
moving along in the earth. Whether or not such causes as these
produce the directive power of the magnetic needle, we cannot here
pretend to decide; they can hardly fail to affect it. The Aurora
Borealis too, probably an electrical phenomenon, is said, under
particular circumstances, to agitate the magnetic needle. It is
not surprising, therefore, that, if electricity have an important
office in the atmosphere, magnetism should exist in the earth. It
seems likely, that the magnetic properties of the earth may be
collateral results of the existence of the same cause by which
electrical agency operates; an agency which, as we have already
seen, has important offices in the processes of vegetable life. And
thus magnetism belongs to the same system of beneficial contrivance
to which electricity has been already traced.
We see, however, on this subject very dimly and a very small way.
It can hardly be doubted that magnetism has other functions than
those we have noticed.