14 Temperature of the Terrestrial Globe. 
imum, we have then twelve thousand meters for the depth ac. Thus, 
in the interior of terra firma, we shall have at this depth a tempera- 
ture of 400° C. admitting that the heat augments from above down- 
wards at a degree for thirty meters depth. But, as we have just 
proved, observation gives us at this depth of the sea a temperature 
of about 0°. What becomes of the 400 degrees which should be 
found there? In order satisfactorily to answer this question in the 
hypothesis, it will be necessary here to quote certain principles of 
M. Fourier. The entire surface of the globe loses the tempera- 
ture, accruing from the incandescent interior, by radiation into the 
infinite space which surrounds it. This loss which when the whole 
globe was still in a state of fusion was very considerable, is at pres- 
ent, and has been for a long time insensible; we may then regard 
the actual temperature of the surface of the globe as constant, and 
the calculation goes back thirty thousand years* the time when this 
temperature was diminished one half.—The water of the ocean Is, as 
well as the body of the earth, a cooling medium, and carries off the 
interior heat by virtue of movements produced by the difference of 
specific gravity, more rapidly than this indefinite space, which occa- 
sions the temperature at the bottom of the ocean tobe so low. Let 
us examine these principles and the consequence to be deduced from 
them. We proceed to radiation, which can only be, asI believe, the 
chemical progression, of caloric in a material medium, as I conceive 
the space of our planetary system to be, since new observations upon 
the comet of Encke have proved that there exists a material sub- 
stance, although imponderable, which occasions a mechanical resist- 
ance to motion in it,—a substance which I have long since hypothet- 
ically admitted as a chemical medium (the radiation) of the light of 
the stars. 
Thus we admit with M. Fourier that the terrestrial globe is con- 
tinually parting with its heat and that this loss may equal the aug- 
mentation caused by the action of the sun and other luminaries, if 
the latter be considered as, of any amount.—Let us proceed to the | 
examination of the cooling of the inferior beds of the sea. 
The cooling of a liquid is produced in two ways, one of which is 
the chemical motion of caloric, the other, the circulation established 
* As M. Fourier bases his calculations upon the cooling of a homogeneous globe 
of iron, we may be assured after what has been said upon the heterogeneous nature 
of the beds in the crust of the earth, that this epoch extends back to at least three 
hundred thousand years. 
