n the proofs of the existence of
a God, in matter, in the laws of motion, and in the nature of light. He
admitted innate ideas, he invented new elements, he created a world; he
made man according to his own fancy; and it is justly said, that the man
of Descartes is, in fact, that of Descartes only, very different from the
real one.

He pushed his metaphysical errors so far, as to declare that two and two
make four for no other reason but because God would have it so. However,
it will not be making him too great a compliment if we affirm that he was
valuable even in his mistakes. He deceived himself; but then it was at
least in a methodical way. He destroyed all the absurd chimeras with
which youth had been infatuated for two thousand years. He taught his
contemporaries how to reason, and enabled them to employ his own weapons
against himself. If Descartes did not pay in good money, he however did
great service in crying down that of a base alloy.

I indeed believe that very few will presume to compare his philosophy in
any respect with that of Sir Isaac Newton. The former is an essay, the
latter a masterpiece. But then the man who first brought us to the path
of truth, was perhaps as great a genius as he who afterwards conducted us
through it.

Descartes gave sight to the blind. These saw the errors of antiquity and
of the sciences. The path he struck out is since become boundless.
Rohault's little work was, during some years, a complete system of
physics; but now all the Transactions of the several academies in Europe
put together do not form so much as the beginning of a system. In
fathoming this abyss no bottom has been found. We are now to examine
what discoveries Sir Isaac Newton has made in it.

LETTER XV.--ON ATTRACTION

The discoveries which gained Sir Isaac Newton so universal a reputation,
relate to the system of the world, to light, to geometrical infinities;
and, lastly, to chronology, with which he used to amuse himself after the
fatigue of his severer studies.

I will now acquaint you (without prolixity if possible) with the few
things I have been able to comprehend of all these sublime ideas. With
regard to the system of our world, disputes were a long time maintained,
on the cause that turns the planets, and keeps them in their orbits: and
on those causes which make all bodies here below descend towards the
surface of the earth.

The system of Descartes, explained and improved