as the Revolution of Jupiter with reſpect to that of the Earth. He proves, that as the Planets make their Revolutions in Elipſis's, and conſequently being at a much greater Diſtance one from the other in their Aphelia, and a little nearer in their Perihelia; the Earth's Velocity, for Inſtance, ought to be greater, when 'tis nearer Venus and Mars, becauſe the Fluid that carries it along, being then more preſs'd, ought to have a greater Motion; and yet 'tis even then that the Earth's Motion is ſlower.
He proves that there is no ſuch Thing as a celeſtial Matter which, goes from Weſt to Eaſt, ſince the Comets traverſe thoſe Spaces, ſometimes from Eaſt to Weſt, and at other Times from North to South.
In fine, the better to reſolve, if poſſible, every Difficulty, he proves, and even by Experiments, that 'tis impoſſible there ſhould be a Plenum; and brings back the Vacuum, which Ariſtotle and Des Cartes had baniſh'd from the World.
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