what Purpoſe are ſo many Calculations to tell us what you yourſelf don't comprehend?
I have taught you, may Sir Iſaac rejoin, that all Bodies gravitate towards one another in proportion to their Quantity of Matter; that theſe central Forces alone, keep the Planets and Comets in their Orbits, and cauſe them to move in the Proportion before ſet down. I demonſtrate to you, that 'tis impoſſible there ſhould be any other Cauſe which keeps the Planets in their Orbits, than that general Phenomenon of Gravity, or heavy Bodies fall on the Earth according to the Proportion demonſtrated of central Forces; and the Planets finiſhing their Courſe according to theſe ſame Proportions, in caſe there were another Power that acted upon all thoſe Bodies, it would either increaſe their Velocity, or change their Direction. Now not one of thoſe Bodies ever has a ſingle Degree of Motion or Velocity, or has any Direction but what is demonſtrated to be the Effect of the cen-
