above 32 degrees F.

If, then, the heat of the earth's centre amount to 450,000 degrees F.,
as M. Cordier deems highly probable, that is to say, about twenty times
the heat of melted iron, even according to Wedgwood's scale, and upwards
of 160 times according to the improved pyrometer, it is clear that the
upper parts of the fluid mass could not long have a temperature only
just sufficient to melt rocks. There must be a continual tendency
towards a uniform heat; and until this were accomplished, by the
interchange of portions of fluid of different densities, the surface
could not begin to consolidate. Nor, on the hypothesis of primitive
fluidity, can we conceive any crust to have been formed until _the
whole_ planet had cooled down to about the temperature of incipient
fusion.

It cannot be objected that hydrostatic pressure would prevent a tendency
to equalization of temperature; for, as far as observations have yet
been made, it is found that the waters of deep lakes and seas are
governed by the same laws as a shallow pool; and no experiments indicate
that solids resist fusion under high pressure. The arguments, indeed,
now controverted, always proceed on the admission that the internal
nucleus is in a state of fusion.

It may be said that we may stand upon the hardened surface of a
lava-current while it is still in motion,--nay, may descend into the
crater of Vesuvius after an eruption, and stand on the scoriae while
every crevice shows that the rock is red-hot two or three feet below us;
and at a somewhat greater depth, all is, perhaps, in a state of fusion.
May not, then, a much more intense heat be expected at the depth of
several hundred yards, or miles? The answer is,--that until a great
quantity of heat has been given off, either by the emission of lava, or
in a latent form by the evolution of steam and gas, the melted matter
continues to boil in the crater of a volcano. But ebullition ceases when
there is no longer a sufficient supply of heat from below, and then a
crust of lava may form on the top, and showers of scoriae may then
descend upon the surface, and remain unmelted. If the internal heat be
raised again, ebullition will recommence, and soon fuse the superficial
crust. So in the case of the moving current, we may safely assume that
no part of the liquid beneath the hardened surface is much above the
temperature sufficient to retain it in a state of fluidity.

It may assist us in forming a clearer