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