d^creafes as you afcend from the Center, and that in the pro- 
portion of tne Squares of the difimces therefrom reciprocally ^ lb 
as at a double diftance to have but a quarter of the force ; this 
property is the principle on which Mr. Newton has made out 
all the Phmomcna of the C^lefiial Motions^ fo eafily and natu- 
rally that its truth is paft difpute. Befides that, it is highly 
rational, that the attractive or gravitating power fhould ex- 
ert it felf more vigiroufly in a fmall Sphere, and weaker in a 
greater, in proportion as it is contracted or expanded, and if 
lo, feeing that the fur faces of Spheres are as the Squares of their. 
Radii J this power at ftveral diftances will be as the Squares 
of thofe difiances Reciprocally^ and then its whole action upoa 
each Spherical Surface^ be it great or frnall will be alwaicsc- 
qual. And this is evidently the rule of Gravitation towards the 
Centers 0? the Sun^ Jupiter^ Saturn and the Earthy andthence 
is reafbnably inferred, to be the general principle obferved by 
Nature, in all the reft of thQ Celejlial Bodies. 
Theft are the principal affeftions of Gravityy from which 
the rules of the /4// of Bodiesy and thQ motJon Projects arc 
Mathamatically deducible. Mr. Jfaac Newton has fliewcd how 
to define the fpaces of the defcent of a Body^ let fall from arty: 
given highth, down to the Center. Suppofing the Gravitation 
to increaft, as in the fifth Property j but confidering the 
fmalnefs of hight, to which any Projedf can be made afcend, 
and over how little an Jrch of the Globe it can be call by any 
of our Engine Sy we may well enough fuppofe thQ Gravity e- 
qual throughout, and the defcents of ProjQ^s in parralei 
line^, which in truth are towards the C^;^^^r, the difference 
being fb finall as by no means to be difcovered in Pra6tice. 
The Oppojition of tilt Jiry 'tis true, is confiderable againft all 
light bodies moving through it, as likewife againft fmall ones 
( of which more liereafter) but in great and ponderous Shot, 
this Impediment is found by £jc/mm^ but very imall, and 
may fafely be neglected. 
Pro- 
