LET. V. OF THE SYSTEM OF Des CaRTES.

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Upon the supposition of an universal pleni-tude, all motion, indeed, is impossible. Forwhatever be the nature of this materia subtilis,whether dense or rare, the whole must be ab-solutely immovable and impenetrable; and fora body to pass through such a medium, wouldbe more difficult than for it to pass through asea of quicksilver, or a rock of adamant.

It was said, by many of the ancient philoso-phers, that nature abhors a vacuum; and bymeans of this absurd dogma, and many othersof the like nature, they attempted to prove andillustrate the doctrine of an universal plenum,like that of Des Cartes. But this is a bare as-sertion, unsupported by facts, and is too idle anotion to require any formal refutation. Andin nearly the same predicament, are most of theother arguments that have been used in defenceof this doctrine. They are all sufficiently ex-posed, not only by the Torrecellian experiment,and the nature of pumps in general, but like-wise from the most plain phænomena of theconstant and free motion of bodies; as wellthose that are in the heavens, as those that arenear the earth’s surface, which come continuallyunder our inspection.

The objections which may be brought againsthis vortices, or whirlpools, are also equallystrong and irrefragable; and show clearly enough,

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