He was not the man to let his mind dwell on the woes and evils of the world; and the follies and perversities which cause them interested him only so far as they provided material for his wit.
It remains, however, noteworthy that the author of the theory of the progress of knowledge, which was afterwards to expand into a general theory of human Progress, would not have allowed that this extension was legitimate; though it was through this extension that Fontenelle's idea acquired human value and interest and became a force in the world.
9.
Fontenelle did a good deal more than formulate the idea.

He reinforced it by showing that the prospect of a steady and rapid increase of knowledge in the future was certified.
The postulate of the immutability of the laws of nature, which has been the indispensable basis for the advance of modern science, is fundamental with Descartes.

But Descartes did not explicitly insist on it, and it was Fontenelle, perhaps more than any one else, who made it current coin.

That was a service performed by the disciple; but he seems to have been original in introducing the fruitful idea of the sciences as confederate and intimately interconnected [Footnote: Roger Bacon, as we saw, had a glimpse of this principle.]; not forming a number of isolated domains, as hitherto, but constituting a system in which the advance of one will contribute to the advance of the others.

He exposed with masterly ability the reciprocal relations of physics and mathematics.