ſame in that caſe as if thoſe attractions did not act at all. by cor. 6. of the laws of motion. And by a like reaſoning if the attraction SN is leſs than the attraction SM, it will take away out of the attraction SM the part SN, ſo that there will remain only the part (of the attraction) MN, to diſturb the proportionality of the area's and times, and the elliptical figure of the orbit. And in like manner if the attraction SN be greater than the attraction SM, the perturbation of the orbit and proportion will be produced by the difference MN alone. After this manner the attraction SN reduces always the attraction SM to the attraction MM the firſt and ſecond attractions perfectly unchanged; and therefore the area's and times come then neareſt to proportionality, and the orbit PAB to the above-mentioned elliptical figure, when the attraction MN is either none, or the leaſt that is poſſible; that is, when the accelerative attractions of the bodies P and T approach as near as poſſible to equality; that is, when the attraction SN is neither none at all, nor leſs than the leaſt of all the attractions SM, but is as it were a mean between the greateſt and leaſt of all thoſe attractions SM. that is, not much greater nor much leſs than the attraction SK. Q. E. D.
Case 2. Let now the leſſer bodies P, S, revolve about a greater T in different planes; and the force LM acting in the direction of the line PT ſituate in the plane of the orbit PAB, will have the ſame effect as before; neither will it draw the body P from the plane of its orbit. But the other force NM acting in the direction of a line parallel to ST (and which therefore what the body S is without the line of the nodes in inclined
