 6. Is the motion of Jupiter and Saturn aberrant and, if so, what are the inequalities in it and what causes them? Newton answered yes, because they interact gravitationally, and the dominant inequality has a period corresponding to the 19 years between their consecutive conjunctions. (The second part of this answer did not appear in the first edition.) By the early 1720s it had become clear that the dominant period in the anomalies of motion of these two planets is not that of the time between conjunctions, but something of much longer duration, giving rise to the questions of what the vagaries actually are and whether they can truly be derived from Jupiter's and Saturn's gravitational forces.