PRIMITIVE HEAT OF THE EARTH. 429 
the stars has established in the regions furrowed indefi- 
nitely by the planets of our system. 
You recollect, Gentlemen, with what delight Fourier 
used to converse on this subject. You know well that he 
thought himself sure of having assigned the temperature 
of space within eight or ten degrees. By what fatality 
has it happened that the memoir, wherein no doubt our 
colleague had recorded all the elements of that important 
determination, is not to be found? May that irreparable 
loss prove at least to so many observers, that instead of 
pursuing obstinately an ideal perfection, which it is not 
allotted to man to attain, they will act wisely in placing 
the public, as soon as possible, in the confidence of their 
labours. 
I should have yet a long course to pursue, if, after 
having pointed out some of those problems of which the 
condition of science enabled our learned colleague to give 
numerical solutions, 1 were to analyze all those which, 
still enveloped in general formule, await merely the data 
of experience to assume a place among the most curious 
acquisitions of modern physics. ‘Time, which is not at 
my disposal, precludes me from dwelling upon such devel- 
opments. I should be guilty, however, of an unpardon- 
able omission, if I did not state that, among the formule 
of Fourier, there is one which serves to assign the value 
of the secular cooling of the earth, and in which there is 
involved the number of centuries which have elapsed 
since the origin of this cooling. The question of the an- 
tiquity of the earth, including even the period of incan- 
descence, which has been so keenly discussed, is thus 
reduced to a thermometric determination. Unfortunately 
this point of theory is subject to serious difficulties. Be- 
sides, the thermometric determination, in consequence of 
its excessive smallness, must be reserved for future ages. 
