Des Cartes said his existence was a fact--a fact above and
beyond all logic; logic could neither prove nor disprove it. The _Cogito
ergo Sum_ was not new itself, but it was the first stone of a new
building--the first step in a new road: from this fact Des Cartes tried
to reach another, and from that others.

The physical principle is that nothing exists but substance, which
he makes of two kinds--the one a substance that thinks, the other a
substance extended. Actual thought and actual extension are the essence
of substance, so that the thinking substance cannot be without some
actual thought, nor can anything be retrenched from the extension of a
thing, without taking away so much of its actual substance.

In his physical speculations, Des Cartes has allowed his imagination
to run very wild. His famous theory of vortices is an example of
this. Assuming extension to be the essence of substance, he denied the
possibility of a vacuum by that assumption; for if extension be the
essence of substance, wherever extension is, there substance must be.
This substance he assumes to have originally been divided into equal
angular particles, each endowed with an equal degree of motion; several
systems or collections of these particles he holds to have a motion
about certain equidistant points, or centres, and that the particles
moving round these composed so many vortices. These angular particles,
by their intestine motions, he supposes to become, as it were, ground
into a spherical form; the parts rubbed off are called matter of the
first element, while the spherical globules he calls matter of the
second element; and since there would be a large quantity of this
element, he supposes it to be driven towards the centre of each vortex
by the circular motion of the globules, and that there it forms a large
spherical body such as the suu. This sun being thus formed, and
moving about its own axis with the common matter of the vortex, would
necessarily throw out some parts of its matter, through the vacuities
of the globules of the second element constituting the vortex; and this
especially at such places as are farthest from its poles: receiving, at
the same time in, by these poles, as much as it loses in its equatorial
parts. And, by these means, it would be able to carry round with it
those globules that are nearest, with the greater velocity; and the
remoter, with less. And, further: those globules which are nearest the
centre of