[Sidenote: Motion and its Cause. Development and Extension of the Conception of Force.] § 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 Agent," and "can be the effect of nothing else than the wisdom and skill of a powerful ever-living Agent who, being in all places, is more able by his will to move the bodies within his boundless uniform _sensorium_, and thereby to form and reform the parts of the universe, than we are by our will to move the parts of our own bodies."[233:7]