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 the Caue that turns the Planets, and keeps them in their Orbits; and on thoe Caues which make all Bodies here below decend towards the Surface of the Earth.

Sytem of Des Cartes explain'd and improv'd ince his Time, eem'd to give a plauible Reaon for all thoe Phænomena; and this Reaon eem'd more jut, as 'tis imple, and intelligible to all Capacities. But in Philoophy, a Student ought to doubt of the Things he fancies he undertands too eaily, as much as of thoe he does not undertand.

, 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 can't perhaps be conceiv'd any otherwie than by Impulion; therefore all thoe Bodies mut be impelled. But by what are they impelled? All Space is full, it therefore is fill'd with a very ubtile Matter, ince this is imperceptible to us;