We should hardly expect so
perfect a rotundity in a body formed by the cool accretion of
solid fragments and particles. It is just what we should expect
in a fluid body, and the later irregularities of the surface are
accounted for by the constant crumpling and wearing of its solid
crust. Many would find a confirmation of this in the phenomena of
volcanoes, geysers, and earthquakes, and the increase of the
temperature as we descend the crust. But the interior condition
of the earth, and the nature of these phenomena, are much
disputed at present, and it is better not to rely on any theory
of them. It is suggested that radium may be responsible for this
subterraneous heat.
The next stage in the formation of the earth is necessarily one
that we can reach only by conjecture. Over the globe of molten
fire the vapours and gases would be suspended like a heavy
canopy, as we find in Jupiter and Saturn to-day. When the period
of maximum heat production was passed, however, the radiation
into space would cause a lowering of the temperature, and a scum
would form on the molten surface. As may be observed on the
surface of any cooling vessel of fluid, the scum would stretch
and crack; the skin would, so to say, prove too small for the
body.
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