Compression, when considered as a consequence of centrifugal force
acting on a rotating mass, explains the earlier condition of fluidity of our
planet. During the solidification of this fluid, which is commonly
conjectured to have been gaseous and primordially heated to a very high
temperature, an enormous quantity of latent heat must have been liberated.
If the process of solidification began as Fourier conjectures, by radiation
from the cooling surface exposed to the atmosphere, the particles near the
center would have continued fluid and hot. As, after long emanation of heat
from the center toward the exterior, a stable condition of the temperature
of the Earth would at length be established, it has been assumed that with
increasing depth the subterranean heat likewise uninterruptedly increases.
The heat of the water which flows from deep borings (Artesian wells), direct
experiments regarding the temperature of rocks in mines, but, above all, the
volcanic activity of the Earth, shown by the flow of molten masses from open
fissures, afford unquestionable evidence of this increase for very
considerable depths from the upper strata. According to conclusions based
certainly upon mere analogies, this increase is probably much greater toward
the center.
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