f LAPLACE; he proved that
the state of our system is _stable_; that is, the ellipsis the planets
describe will always remain nearly circular, and the axis of revolution
of the earth will never deviate much from its present position. He also
gave a mathematical proof that this stability is not accidental, but the
result of design, of an arrangement by which the planets all move in the
same direction, in orbits of small eccentricity and slightly inclined to
each other. Reasoning from analogy, as the author of the _Vestiges_ is
prone to do--extending our views from our solar system to other
systems--other suns and revolving planets--it is fair to conclude that
they are not less perfect in arrangement--subject to like conditions of
permanency, and alike exempt from mutation, decay, collision, or
extinction.

Descending from this high region, we accompany the author to his next
and lower field--the

EARTH AND ITS GEOLOGICAL HISTORY.

Our globe is somewhat less than 8,000 miles in diameter; it is of a
spheroidal form, the equatorial exceeding the polar axis in the
proportion of 300 to 299, and which slight inequality, in consequence of
its diurnal revolution, is necessary to preserve the land near the
equator from inundation by the sea. The mean density or average weight
of the earth is, in proportion to that of distilled water, as 5.66 to 1.
So that its specific gravity is considerably less than that of tin, the
lightest of the metals, but exceeds that of granite, which is three
times heavier than water.

Descending below the surface, the first sensation that strikes is the
increase of temperature. This is so rapid, that for every one hundred
feet of sinking we obtain an increase of more than one degree of
Fahrenheit's thermometer. If there be no interruption to this law, and
no reason exists to conclude there is, it is manifest that at the depth
of a few miles we must reach an intensity of heat utterly unbearable.
Hence it follows that by no improvements in machinery can mining
operations be carried down to a great depth below the surface. The
greatest depth yet penetrated does not exceed three thousand feet, and
forms a very small advance towards the earth's centre, distant 4,000
miles.

Geologists, however, without penetrating far into the earth, have found
means for obtaining an insight for several miles into its interior
structure, and armed with hammer, chisel, and climbing hook, they
explore the beetling sea-