 8. What precisely is the motion of the Moon, and what gives rise to the inequalities in it, inequalities not observed in the motions of the satellites of Jupiter and Saturn? Newton's answer to the second part is the perturbing effect of the Sun's gravity, leaving the answer to the first in the form of a promissory note: work out all the perturbations from solar gravity, and you will have the answer. The major open question was whether the complex motion of the line of apsides and the inequality known as the evection — the two features for which the Horrocksian cinematic model that Newton had employed in the Scholium to Book 3, Proposition 35 had resorted to an old-fashoined epicycle — can be derived from the action of solar gravity.