assumed for the interior of the earth constant conditions. It
is now generally accepted that this is not probable, and that
whether it cooled from a gas or coagulated from planetesimals,
it became solid first at the center which then would be
hottest, and both Becker[3] and A. Holmes[4] assume an initial
temperature gradient. If that gradient were greater than the
gradient of steady flow the conditions of steady flow would be
approached most rapidly at the exterior, the loss of heat and
energy would be altogether from within and it is easy to
arrange for conditions mathematically in which almost all the
loss of energy would come from the very interior, near the
center. What will be the effect? A paradoxical one, if the part
outside the center is rigid enough to be self-sustaining. The
central core will become a gas!

[3] Bull. Geol. Soc. Am., Vol. 26, 1915, p. 197, etc.
[4] Geological Magazine, March and April, 1913.



This is so contrary to our ordinary experience and ideas, in
which loss of heat tends to change from gas to fluid and solid,
that we must look into it a little to make it sound reasonable.
The recent brilliant work of P. W. Bridgman (contrary to the
earlier speculations of Tammann) indicates that the effect of
increased pressure, at high temperature, makes a substance
solid and crystalline. Crowd any atoms close enough together,
and no matter how fast they expand or contract under the
influence of heat the crystalline atomic forces will get to
work when they are crowded within their range, and the closest