34 A VI 8 INERTIAE

of any fluid matter upon it, and therefore thegravity of it, ought to be the greater: whichis directly contrary to experience. These rea-sons, abstracting from those aboveN° 14,15and 16, strew that gravity is not the actionof matter upon matter, but the vertue andpower of an immaterial cause, orbeing, con-stantly imprested upon it (k).

XVIII. To

(h) After all that hath been said, there is a difficulty stillurged with respect to gravity, which with much submissi-on I humbly beg leave to consider. It is said, Sir IsNewton, at the end of the last edition os his Optics , givesmany reasons , which induced him to believe there was asubtile elastic fiuid, which might be the cause os gravity,and the cause of many other phanomena , particularly thoseof heat and light , at the same time. By reducing morepheenomena to one principle, cause, or instrument, the beau~iy of nature is set in a greater luslre. Though this princi-ple may be immediately deducedfrom the first cause , s’Grave-sande’r arguments da not hold against this fluids as Sir 1 -saac describes it. As it pierces all bodies and touches theirelements, or leaf particles, it may ait on them with a forceproportional to their number, or to the matter of the body oflwhich it acts. It is rarer in great bodies than in smallones, and therefore ?nay act with a force proportional to thebody towards which it impels. To begin with the last ofthese reasons: It doth not appear sufficient, in order to ac-count how this fluid may act with a force proportional tothe body to which another is impelled, to aflert that i £is rarer in great bodies than in small ones: it must be

farther