Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 2.djvu/533

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It hould have been aid, that whenf' S 1 the Moon is in any place of its orbit, uppoe omewhere at N, in that half of the orbit which is next the Sun, it then being nearer the Sun than the Earth, has thereby a greater gravity to the Sun, than the Earth: which exces of gravity, according to Sir I/bac Nefwton's method, coniifts of two arts; one acting in the line N IC paraiiel to that which joins the Earth and Sun; and the other acting, in the line If B directed to the Earth, and thee two forces, being compounded into one, make a force directed in the line NB; which is in proportion to the force of gravity, as that line NB is to TB nearly. Wherefore, as there is a force contantly impelling the. Moon, ” fpmewhere towards the point B, this force is uppoed to iniiect the motion of the Moon into a curve line about that point; for the ame reaon as the gravity of it to the Earth, is uppoed to infiect its motion into a curve line about the Earth: not that the Moon can actually have o many diftinct motions, but the one imple motion of the Moon round the Sun is fitp ofed to arie »frotn a compoition of thee everal motions, In