French Mathematician and Astronomer, is said to have demonstrated that the mean temperature of the earth, cannot have diminished more than one fifth of a degree within the last two thousand years. The mean temperature of the interior portions of the earth, supposing that temperature to have been once greatly elevated, must have long since fallen very nearly to the medium temperature of the surface. It is true that this conclusion, taken in connection with the admission that the earth was once intensely heated, requires us to suppose that it has existed through a period of immense and inconceivable length. But this is precisely what all the researches and discoveries of geology demonstrate. They do not attempt to assign, or even conjecture the length of the periods which elapsed during the various formations. They simply regard them as immense cycles extending back through the broad expanse of ages. The thought may seem to overwhelm and oppress the imagination; yet, I see not how to avoid the conclusion,—geological facts, astronomical observations, and mathematical demonstrations all confirm it—that the earth has been in existence so long that though once heated to a fluid state, its interior portions have not only become consolidated, but that their mean temperature has fallen so low, that there has been no measurable decrease for the last two thousand years. Of course I do not mean to say that the decrease in the earth's temperature, has been mathematically equal to nothing, nor even less than any assignable quantity, such a supposition would require us to regard the period of its past existence, as being greater than any assignable quantity, that is practically thought not absolutely equal to infin ity. But what I do insist upon as being plainly demonstrable in the manner indicated above, is that the decrease of temperature has been so small, as to justify us in regarding the medium temperature of the interior portions of the earth as being very nearly the same with that of its surface.
We will therefore dismiss this question, and with the rea-
