252 Marcel de Serres on the Old World 
been uniform everywhere, and that the sun had not yet re- 
gulated and determined climates. The earth had not then 
need of his rays, since terrestrial temperatures depended on 
an entirely different cause. Their effect was to render cli- 
mates generally alike, as well as the natural productions to 
whose development they were alone favourable. 
This primitive uniformity could not, however, continue : 
it accordingly ceased altogether on the appearance of Man. 
If it had lasted, it would have partially destroyed the phy- 
sical and intellectual energy of our species. It likewise 
proves that, independently of the heat which the earth owes 
to the sun, it derives it also from another source. That 
source is in its own bosom, and its action has for a long 
time regulated, almost of itself, the greater part of terres- 
trial phenomena. The central heat, which with Buffon 
was only an hypothesis, must now be regarded as a fact 
almost demonstrated. . | 
It is so, more especially by this remarkable circumstance, 
that the heat, instead of diminishing below the terrestrial 
strata, where the calorific rays of the sun are no longer felt, 
increases in proportion to the depth (See Note 8). It is 
still further evinced by volcanic eruptions, and the constant 
temperature of thermal springs, These phenomena clearly 
indicate that a powerful source of heat must exist in the 
interior of the globe. We find, moreover, a new proof of 
the same thing in the general form of the earth, which has 
not depended solely on the movement imparted to it, but on 
its primitive liquidity (See Mote 9). The earth has not . 
derived this liquidity from water nor any other solvent, but 
rather from the action of a high temperature. This tem- 
perature is singularly diminished since the origin of things ; 
it does not, at least at the present time, affect the heat of 
the surface more than the thirtieth part of a centigrade 
degree. 
It may be safely affirmed, that if the earth lost entirely 
this degree of heat, which it does not derive from the sun, 
it would not, on that account, become an inert and frozen 
globe, as Buffon supposed, when he expressed his belief that 
