deſcribe equal ſpaces in equal times; and this is yet more accurately proved by the experiments of pendulums.
The attractive forces of bodies at equal diſtances, are as the quantities of matter in the bodies. For ſince bodies gravitate towards the Earth, and the Earth again towards bodies with equal moments; the weight of the Earth towards every body, or the force with which the body attracts the Earth, will be equal to the weight of the ſame body towards the Earth. But this weight was ſhewn to be as the quantity of matter in the body; and therefore the force with which every body attracts the Earth, or the abſolute force of the body, will be as the ſame quantity of matter.
Thefore the attractive force of the entire bodies ariſes from, and is compounded of, the attractive forces of the parts, becauſe as was juſt ſhewn, if the bulk of the matter be augmented or diminiſhed, its virtue is proportionably augmented or diminiſhed. We muſt therefore conclude that the action of the Earth is compounded of the united actions of its parts; and therefore that all terreſtrial bodies muſt attract each other mutually, with abſolute forces that are as the matter attracting. This is the nature of gravity upon Earth; let us now ſee what it is in the Heavens.
That every body perſeveres in its ſtate either of reſt, or of moving uniformly in a right line, unleſs in ſo far as it is compelled to change that ſtate by forces impreſſed, is a law of nature univerſally received by all philoſophers. But from thence it follows that bodies which move in curve lines, and are therefore continually going off from the right
lines that are tangents to their orbits, are by ſome
