gram (fig. 92);
whereas, if the other or less correct scale be adopted, we should meet
with it at some point between the two circles; the space between them,
together with the lines themselves, representing a crust of 200 miles in
depth. In either case, we must be prepared to maintain that a
temperature many times greater than that sufficient to melt the most
refractory substances known to us, is sustained at the centre of the
globe; while a comparatively thin crust, resting upon the fluid, remains
unmelted; or is even, according to M. Cordier, increasing in thickness,
by the continual addition of new internal layers solidified during the
process of refrigeration.

The mathematical calculations of Fourier, on the passage of heat through
conducting bodies, have been since appealed to in support of these
views; for he has shown that it is compatible with theory that the
present temperature of the surface might coexist with an intense heat at
a certain depth below. But his reasoning seems to be confined to the
conduction of heat through solid bodies; and the conditions of the
problem are wholly altered when we reason about a fluid nucleus, as we
must do if it be assumed that the heat augments from the surface to the
interior, according to the rate observed in mines. For when the heat of
the lower portion of a fluid is increased, a circulation begins
throughout the mass, by the ascent of hotter, and the descent of colder
currents. And this circulation, which is quite distinct from the mode in
which heat is propagated through solid bodies, must evidently occur in
the supposed central ocean, if the laws of fluids and of heat are the
same there as upon the surface.

In Mr. Daniell's experiments for obtaining a measure of the heat of
bodies at their point of fusion, he invariably found that it was
impossible to raise the heat of a large crucible of melted iron, gold,
or silver, a single degree beyond the melting point, so long as a bar of
the respective metals was kept immersed in the fluid portions. So in
regard to other substances, however great the quantities fused, their
temperature could not be raised while any solid pieces immersed in them
remained unmelted; every accession of heat being instantly absorbed
during their liquefaction. These results are, in fact, no more than the
extension of a principle previously established, that so long as a
fragment of ice remains in water, we cannot raise the temperature of the
water