it swims on Water, any more than Iron , because it swims on Mercury .
Fifthly, That this Power increases as you descend, and decreases as you ascend from the Center, and that in the Proportion of the Squares of the Distances therefrom reciprocally, so as at a double Distance to have but a quarter of the Force; this Property is the Principle on which Mr. Newton has made out all the Phænomena of the Cœlestial Motions, so easily and naturally, that its Truth is past Dispute. Besides that, it is highly rational, that the attractive or gravitating Power should exert it self more vigorously in a small Sphere, and weaker in a greater, in proportion as it is contracted or expanded; and if so, seeing that the Surfaces of Spheres are as the Squares of their Radii, this Power, at several Distances, will be as the Squares of those Distances reciprocally; and then its whole Action upon each Spherical Surface, be it great or small, will be always equal. And this is evidently the Rule of Gravitation
towards the Centers of the Sun, Jupiter, Saturn and the Earth, and thence is reasonably inferred, to be the general Principle observed by Nature, in all the rest of the Cœlestial Bodies.
These are the principal Affections of Gravity , from which the Rules of the Fall of Bodies , and the Motion of Projects are Mathematically deducible. Mr. Isaac Newton has shew'd how to define the Spaces of the Descent of a Body , let fall from any given height, down to the Center , supposing the Gravitation to increase, as in the fifth Property; but considering the smallness of heighth, to which any Project can be made ascend, and over how little an Arch of the Globe it can be cast by any of our Engines , we may well enough suppose the Gravity equal throughout, and the Descents of Projects in parallel Lines, which in Truth are towards the