In applying the theory to the magnetism of the earth, we must bear in
mind that the earth is probably magnetic by induction, and not in virtue
of its own specific action. The rotation of the surrounding ether, and
the consequent production of a radial stream, calls the ether into
motion within the earth's interior, as well as on the surface; but it
does not follow that the ether shall also enter the earth at its poles
and escape at its equator, for the obliquity of the vortex would
interfere with this result. It is sufficient that this does occur in the
terral vortex immediately surrounding the earth. From late experiments
it is pretty well established that the axial direction of the needle,
(and of other bodies also,) is due to peculiar internal arrangement in
laminae or layers, the existence of which is favorable to the passage of
the magnetic current.
According to the experiments[27] of Dr. Tyndal, it is found that the
magnetism of a body is strongest along the line of greatest density. As,
therefore, the laminae of bodies may be considered planes of pressure,
when these planes are suspended horizontally, the directive force is
greatest, and the longest diameter of the body sets axial. On the other
hand, when the body was suspended so that the laminae were vertical, the
longest diameter set equatorial. Now, we know that the crust of the
earth is composed of laminae, just as the piece of shale in Doctor
Tyndal's experiments, and that these layers are disposed horizontally.
And whatever force originally arranged the land and water on our globe,
it is evident that the continents are longest from north to south, and
therefore correspond to the natural direction of the magnetic force.
In consequence of the intrinsic difficulties of this question, and the
mystery yet attaching to it, we may be permitted to enter a little more
minutely into it, and jointly consider other questions of interest, that
will enable us to refer the principal phenomena of terrestrial magnetism
to our theory.
We have before adverted to the discrepancies in the earth's compression,
as determined by the pendulum, and also to the uncertainty of the moon's
mass, as deduced from the nutation of the earth's axis. It is also
suspected that the southern hemisphere is more compressed than the
northern; and other phenomena also point out the inadequacy of the law
of gravitation, to account for the figure of the earth.
From the invariability of the axis of rotation, we must conclude that
whatever form is the true form, it is one of equilibrium. In casting our
eyes over the map of the world, we perceive that the surface is very
unequally divided into land and sea; and that the land is very unequally
arranged, both north and south, and east and west. If we compare the
northern and southern hemisphere, we find the land to the water about 3
to 1. If we take the Pacific portion, and consider the north end of New
Zealand as a centre, we can describe a great circle taking in one half
the globe, which shall not include one-tenth of the whole land. Yet the
average height of the remaining nine-tenths, above the level of the sea,
is nearly 1,000 feet. Call this nine-tenths nearly equal to one-fourth
of the whole surface, and the protuberant land in the hemisphere,
opposite the South Pacific, amounts to 1/30,000 part of the whole mass
of the earth, or about 1/700 of the mass of the moon. Again, the mean
density of the earth is about 5 1/2--water being unity,--and the mean
density of the surface land is only about half this: but three-fourths
of the whole surface is water. Hence, we see that the materials of the
interior of the earth must be either metallic or very compressible. To
assign a metallic nucleus to the earth, is repugnant to analogy; and it
is not rendered even probable by facts, as we find volcanic emissions to
contain no heavier elements than the sedimentary layers. Besides, there
are indications of a gradual increase of density downwards, such as
would arise from the compressibility of the layers. Seeing, therefore,
the equilibrium of the whole mass, and the consequent hydrostatic
balance of the land in the sea,--seeing also the small compressibility
of the solid portions, and the great compressibility of the fluid, the
inference is legitimate that the whole is hydrostatically balanced, and
that our globe is a globe of water, with an intermediate shell of land,
specifically lighter than the fluid in which it is suspended. Where this
shell is of great thickness, it penetrates to greater depths, and
attains to greater elevations above the surface of the aqueous globe;
where it is less thick, it is found below the surface, and forms the
bottom of the upper ocean. Recent soundings give much greater depths to
some parts of the ocean, than the most elevated land upon the globe.
Captain Denham, of H. B. M. ship Herald, lately sounded in 37d south and
37d west, and found bottom at 7,706 fathoms, or about nine English
miles.
As the interior portions of our globe are totally unknown, and the
compressibility of water is well established, it is just as sane to
consider water the most abundant element of nature, as solid land. The
great question to ask is, whether there may not be other phenomena
incompatible with this supposition? It is plain that the permanency of
terrestrial latitudes and longitudes would be unaffected by the
conditions we have supposed. Would the precession of the equinoxes be
also unaffected? Mr. Hopkins has entered into such an investigation, and
concludes: "Upon the whole, then, we may venture to assert that the
minimum thickness of the crust of the globe, which can be deemed
consistent with the observed amount of precession, cannot be less than
one-fourth or one-fifth of the radius of the earth." These
investigations were made on the hypothesis of the interior fluidity
being caused by the fusion of the central portions of a solid globe; but
it is evident that the analytical result would be the same if these
central parts were water, inclosed by an irregularly-spherical shell of
land. Nor would the result be affected, if we considered certain
portions of the interior of this solid shell to be in a state of fusion,
as no doubt is the case.
May not the uncertainty of the mass of the moon, be owing to the fact
that this shell is not so rigidly compacted but that it may yield a
little to external force, and thus also account for the tides in the
Pacific groups, rather obeying the centrifugal force due to the orbit
velocity of the earth, than the attraction of the moon?
Since the days of Hipparchus the sidereal day has not diminished by the
hundredth part of a second; and, consequently, seeing that the
contraction of the mass must be limited by the time of rotation, it is
inferred that the earth has not lost 1/508th of one degree of heat since
that time. This conclusion, sound as it is, is scarcely credible, when
we reflect on the constant radiation into a space 60d below zero. Admit
that the globe is a globe of water, whose average temperature is the
temperature it receives from the sun, and the difficulty vanishes at
once. Its diameter will be invariable, and the only effect of the
cooling of the solid parts will be to immerse them deeper in the water,
to change the _relative_ level of the sea without changing its volume.
This is no puerile argument when rightly considered; but there is
another phenomenon which, if fairly weighed, will also conduct us to the
same views.
It is now a fact uncontroverted, that the sea does actually change its
level, or rather, that the elevation of continents is not only apparent
but real. The whole coast of Sweden and Finland is rising at the present
day at the rate of four feet in a century, while on the south a contrary
effect is produced. Various hypotheses have been formed concerning this
interesting fact. Yet from the indications of geology, it must have been
an universal phenomenon in the early ages of the world, in order to
account for the emersion of sedimentary deposits from the fluid which
deposited them. May not internal fires be yet spreading, and the
continents expanding instead of contracting? And may there not be an
inequality in this process, so as necessarily to immerse in one
direction nearly as much as to elevate in another? One fact is certain,
the elements are scattering the materials of the land along its Oceanic
coasts, which of itself must produce a very minute effect in disturbing
the hydrostatic balance; but a more efficient agent is the earthquake
and volcano.
The upheaving of tracts of land by earthquakes, as on the coast of Chili
would thus be satisfactorily explained, by attributing a certain
resistance due to cohesion or friction preventing a _gradual_ change of
level, but producing it suddenly by the jar of the earthquakes. May we
not inquire also, whether the facility with which the earth seems moved
by this destructive agent, does not point to the same solution as the
irregularity of the figure of the earth?
This is a subject on which it is allowable to speculate, especially if
any light can be thereby thrown on the still more mysterious source of
terrestrial magnetism. It is for such a purpose that we have permitted
ourselves to digress from that subject. In this connection we also may
acknowledge our indebtedness to the sacred volume for the first germ of
this theory of the weather.
Believing in the authenticity of the Mosaic history of the deluge, the
author found it difficult to refer that event to other than natural
causes, called into action by the operation of other causes, and all
simultaneous with the going forth of the fiat of Omnipotence. Thus
reasoning, he was led to regard the deluge as a physical phenomenon
inviting solution, and as a promising exponent to the climatology of
the early world. He looked upon the bow of promise, as the autograph of
the Creator, the signature to a solemn bond, upon which the eye of man
had never before rested. But if there was no rainbow before the deluge,
there was no rain; and following up this clue, he was not only enabled
to solve the problem, but also led to the true cause, which produces the
principal commotions in our atmosphere.
Science boasts of being the handmaid of religion; yet there are names of
note in her ranks who have labored rather to invest this phenomenon with
the mantle of fable, and to force it into collision with the records
graven on the rocky pages of geognosy. But the world is ever prone to be
captivated by the brilliancy of misapplied talents, instead of weighing
merit by its zeal in reconciling the teachings of those things which are
seen, with those which are revealed.
If our globe be constituted as we suppose, the land might experience
repeated submersions, without involving the necessity of any great
departure from established laws. And we might refer to the historical
record of one of these, with all the minute particulars as positive
data, imposing on us the necessity of admitting that the solid parts of
the globe are hydrostatically balanced in the sea. But, modern science
is not always correctly defined when called the pursuit of truth, nor
human learning the means of discovering it.
If we could divest ourselves of this prejudice, we should have a ready
solution of the difficulty presented by the earth having two north
magnetic poles, and probably two also in the south. For, by regarding
the old and new continents as two distinct masses of land whose bases
are separated by 6,000 miles of water, we recognize two great magnets,
dependent, however, for their magnetism, on the rotation of the terral
vortex.
This is no place to enter into a lengthy discussion of such a difficult
subject as magnetism, but we may be allowed to enter a protest against
the current theory of electro-magnetism, viz.: that a force is generated
by a galvanic current at right angles to the producing cause, which is
contrary to the fundamental principles of mechanics. We may conceive
that a current is induced from or to the surrounding space by the
rarefaction or condensation attending the transmission of such a current
along a wire, and that rotation should follow, just as a bent pipe full
of small holes at the lower end, and immersed in water as a syphon, will
generate a vorticose motion in the water; but mere juxtaposition,
without participation and communication with the general current, is
irrational, and, therefore, not true.
We have always regarded a magnetic needle as a part of the great natural
magnet, the earth; that its north pole actually points to the north, and
its south pole to the south; and, being free to move, it is affected by
the circular motion of the surrounding ether, and by every motion by
which the ether is directed. If there was any attraction between the
earth and the needle, opposite poles would be presented, but it is not
so--the force is merely directive.