36 Jl vis inertiae

change of its present state of rest or motion,

is

receive their gravitation by being impinged upon : whichdoes not suit with the phænomena of motion in genera],and with the motion of pendulums in particular, andgives Dr. s’Gravesande’s arguments before cited greatstrength; but it seems then that throwing gold, or anyheavy body upward, against the impulse of this fluid,would be like throwing gold through gold. And sincethis medium must be as dense when it impels cork, aswhen it impels gold, to throw a piece of cork upward,must be as if we endeavoured to make cork penetrate amedium as dense as gold. The expedient found out tomake this medium appear more probably the cause ofgravity, hath been to imagine all bodies exceedingly po-rous and rare : and this notion is carried so extravagant-ly high, as to suppose that all the matter in the known u-niverse might not take up one cubical inch of space, ("SeeDr. Pemlerton’i, Review of Si r Is Newton’s philosophy,I. 3. ch. 2. at the end : aud what is said concerning aprogreflioh of pores by Sir Isaac Newton himself, at theend of his Optics). But might not one fay, that this 'is contriving one hypothesis to support another hypothe-sis, and then contending (in the present objection, Imean) for the reality of both ? Besides, it no way takesoff the difficulty I just now urged, that the fluid must beas dense as the very densest body to give every particleits impulse of gravity. But then what is to be said, st"we suppose a body perfectly solid, or without any pores ?Gravity is allowed on all hands to be as the quantity ofsolid matter. Now if there were a cubick inch of sucha perfectly solid body, and a cubick inch of a body that