y contrasting theories thus appear: that which defines matter
as a continuous substance coextensive with space; and that which defines
it as a discrete substance divided by empty space. But both theories are
seriously affected by the peculiarly significant development of the
conception of force.

[Sidenote: Motion and its Cause. Development and Extension of the
Conception of Force.]

Sect. 107. In the Cartesian system the cause of motion was pressure
within a plenum. But in the seventeenth century this notion encountered
the system of Newton, a system which seemed to involve action at a
distance. In the year 1728 Voltaire wrote from London:

"When a Frenchman arrives in London, he finds a very great
change, in philosophy as well as in most other things. In
Paris he left the world all full of matter; here he finds
absolute vacua. At Paris the universe is seen filled up with
ethereal vortices, while here the same space is occupied with
the play of the invisible forces of gravitation. In Paris the
earth is painted for us longish like an egg, and in London it
is oblate like a melon. At Paris the pressure of the moon
causes the ebb and flow of tides; in England, on the other
hand, the sea gravitates toward the moon, so that at the same
time when the Parisians demand high water of the moon, the
gentlemen of London require an ebb."[232:6]

But these differences are not matters of taste, nor even rival
hypotheses upon an equal footing. The Newtonian system of mechanics, the
consummation of a development initiated by Galileo, differed from the
vortex theory of Descartes as exact science differs from speculation and
unverified conjecture. And this difference of method carried with it
eventually certain profound differences of content, distinguishing the
Newtonian theory even from that of Democritus, with which it had so much
in common. Although Democritus had sought to avoid the element of
purposiveness in the older hylozoism by referring the motions of bodies
as far as possible to the impact of other bodies, he nevertheless
attributed these motions ultimately to _weight_, signifying thereby a
certain _downward disposition_. Now it is true that in his general
belief Newton himself is not free from hylozoism. He thought of the
motions of the planets themselves as initiated and quickened by a power
emanating ultimately from God. They are "impressed by an intelligent
A