" It seems more
probable to this great geometer that the solidification began in the parts
lying nearest to the center: "the phenomenon of the increase of heat with
the depth does not extend to the whole mass of the Earth, and is merely a
consequence of the motion of our planetary system in space, of which some
parts are of a very different temperature from others, in consequence of
stellar heat (chaleur stellaire)." Thus, according to Poisson, the warmth
of the water of our Artesian wells is merely that which has penetrated into
the Earth from without; and the Earth itself "might be regarded as in the
same circumstances as a mass of rock conveyed from the equator to the pole
in so short a time as not to have entirely cooled. The increase of
temperature in such a block would not extend to the central strata." The
physical doubts which have reasonably been entertained against this
extraordinary cosmical view (which attributes to the regions of space that
which probably is more dependent on the first transition of matter
condensing from the gaseo-fluid into the solid state) will be found
collected in Poggendorf's 'Annalen', bd. xxxix., s 93-100.
It is with the greatest difficulty that our powers of comprehension can
conceive the boundary line which divides the fluid mass of the interior from
the hardened mineral masses of the external surface, or the gradual increase
of the solid strata, and the condition of semi-fluidity of the earthy
substances, these being conditions to which known laws of hydraulics can
only apply under considerable modifications.
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