air 
On the Physical Geology of the United States, §c. 287 
rior more rapidly than the interior, and that this external diminu- 
tion has nearly reached its limit, so that the caloric radiated by the 
earth exceeds that derived from the sun and from space by a 
quantity sufficient to melt about three metres in depth (about ten 
feet) in one hundred years.* This diminution of temperature 
would progress most rapidly in a decreasing ratio up to a certain 
limit, after which the internal temperature would begin to dimin- 
ish most rapidly, while the exterior remained nearly uniform. 
‘Three reasons may be adduced why the interior should di- 
minish more in temperature after the above-mentioned limit is 
passed, viz. 
1st. The more imperfect conducting power of the solid exte- 
rior, than the carrying power of the fluid interior. 
2d. The solid exterior having parted with a portion of its ca- 
loric, serves to conduct merely the excess of interior heat to the 
exterior, whence it radiates into space ; and this quantity radiated 
and conducted is nearly uniform, and maintains a temperature 
nearly uniform in the exterior crust of the globe, while the inte- 
rior may undergo great variations. 
3d. The surface from which the radiation takes place, is greater 
than the surface of any contained spherical mass from which it 
draws its caloric for radiation. 
The earth is in a state of nearly uniform exterior temperature 
so far as internal heat is concerned, and while the exterior solid 
part of the earth undergoes little change in its bulk from loss of 
temperature, the interior is gradually diminishing, causing col- 
lapse of the solid exterior upon the fluid interior; and in conse- 
quence of this solid part being too large to embrace the nucleus 
closely, elevation of islands, mountains and continents in some 
parts, and subsidence to a still greater extent in other parts, would 
seem to be the necessary consequences. 
In the other case, where the crust or exterior solid part cooled 
and shrunk most rapidly, it may reasonably be supposed to have 
eracked open in fissures, and the subjacent fluid to have risen in 
the fissures to a height inversely proportioned to its density, as 
water does in the cracks of ice. This supposition, which seems 
a necessary result from the known laws of nature, harmonizes 
* Baron Fourier, Annales de Chimie et de Physique; also a translation of 
a part of the above memoir in the American Journal of Science, Vol. xxxu, 
, pp. 1-19. 
