  In spite of extravagant claims made about the Principia by some in the years after it first appeared — “… he seems to have exhausted his Argument, and left little to be done by those that shall succeed  him”[1] — the most positive view of it that anyone could have substantiated during the first half of the eighteenth century would have emphasized its promise more than its achievements. The theory of gravity had too many loose ends, the most glaring of which was a factor of 2 discrepancy in the mean motion of the lunar apogee, a discrepancy that undercut the claim that the Moon is held in orbit by an inverse-square force. No one knew these loose ends better than Newton himself, yet no one had a greater sense of the potential of the theory of gravity to resolve a whole host of questions in planetary astronomy — which may well explain why he made these loose ends difficult to see except by the most technically skilled, careful readers. Between the late 1730s and the early 1750s the situation changed dramatically when several of the loose ends were tied up, in some cases yielding such extraordinary results as the first truly successful descriptive account of the motion of the Moon in the history of astronomy. During the second half of the eighteenth century the promise of the Principia was not only universally recognized by those active in empirical research, but a large fraction of this promise was realized. What we now call “Newtonian mechanics” emerged in this process, as did the gravity-based accounts of the often substantial divergences of the planets from Keplerian motion, the achievement of Newton's theory of gravity that ultimately ended all opposition to it.