since his time, seemed to
give a plausible reason for all those phenomena; and this reason seemed
more just, as it is simple and intelligible to all capacities. But in
philosophy, a student ought to doubt of the things he fancies he
understands too easily, as much as of those he does not understand.

Gravity, the falling of accelerated bodies on the earth, the revolution
of the planets in their orbits, their rotations round their axis, all
this is mere motion. Now motion cannot perhaps be conceived any
otherwise than by impulsion; therefore all those bodies must be impelled.
But by what are they impelled? All space is full, it therefore is filled
with a very subtile matter, since this is imperceptible to us; this
matter goes from west to east, since all the planets are carried from
west to east. Thus from hypothesis to hypothesis, from one appearance to
another, philosophers have imagined a vast whirlpool of subtile matter,
in which the planets are carried round the sun: they also have created
another particular vortex which floats in the great one, and which turns
daily round the planets. When all this is done, it is pretended that
gravity depends on this diurnal motion; for, say these, the velocity of
the subtile matter that turns round our little vortex, must be seventeen
times more rapid than that of the earth; or, in case its velocity is
seventeen times greater than that of the earth, its centrifugal force
must be vastly greater, and consequently impel all bodies towards the
earth. This is the cause of gravity, according to the Cartesian system.
But the theorist, before he calculated the centrifugal force and velocity
of the subtile matter, should first have been certain that it existed.

Sir Isaac Newton, seems to have destroyed all these great and little
vortices, both that which carries the planets round the sun, as well as
the other which supposes every planet to turn on its own axis.

First, with regard to the pretended little vortex of the earth, it is
demonstrated that it must lose its motion by insensible degrees; it is
demonstrated, that if the earth swims in a fluid, its density must be
equal to that of the earth; and in case its density be the same, all the
bodies we endeavour to move must meet with an insuperable resistance.

With regard to the great vortices, they are still more chimerical, and it
is impossible to make them agree with Kepler's law, the truth of which
has been demonstrated. Sir