ing to the force of its gravity, and the velocity of its motion. The leſs its gravity is, for the quantity of its matter, or the greater the velocity with which it is projected, the leſs will it deviate from a rectilinear courſe, and the farther it will go. If a leaden ball, projected from the top of a mountain by the force of gunpowder, with a given velocity, and in a direction parallel to the horizon, is carried in a curved line to the diſtance of two miles before it falls to the ground; the ſame, if the reſiſtance of the Air were taken away, with a double or decuple velocity, would fly twice or ten times as far. And by increaſing the velocity, we may at pleaſure increaſe the distance to which it might be projected, and diminiſh the curvature of the line which it might deſcribe, till at last it should fall at the diſtance of 10, 30, or 90 degrees, or even might go quite round the whole Earth before it falls; or laſtly, ſo that it might never fall to the Earth, but go forwards into the Celeſtial Spaces, and proceed in its motion in infinitum. And after the ſame manner that a projectile, by the force of gravity, may be made to revolve in an orbit, and go round the whole Earth, the Moon alſo, either by the force of gravity, if it is endued with gravity, or by any other force, that impells it towards the Earth, may be continually drawn aſide towards the Earth, out of the rectilinear way, which by its innate force it would purſue; and be made to revolve in the orbit which it now deſcribes; nor could the Moon without ſome ſuch force, be retain'd in its orbit. If this force was too ſmall, it would not ſufficiently turn the Moon out of a rectilinear course: if it was too great, it would turn it too much, and draw down the Moon from its orbit towards the Earth. It is neceſſary, that the force be of a juſt quantity, and it belongs to the Mathematicians to find the force,
