210

Sir I s A a c N e w t o n’s Book II.

the plane QV R and the plane A B C ; so that the point I will fallbetween B and R; and drawing IT W, the point W will be far-ther remov’d from A than Q. But it is evident, that the plane,which passes through the earth T, and touches the line A G Iin the point I, will cut the plane of the earth’s motion ABCDin the line IT W, and be inclined to the fame in the angle un-der HIB; so that the node, which was first in A, after havingpassed into L, N and Q., comes at last into the point W; as thenode which was at first in C has passed successively from thencethrough the points M, 0 and R to I: but the angle under HIB,which is now the inclination of the orbit to the plane of theecliptic, is manifestly not less than the angle under E C B orEAB, but rather something greater.

30. Thus the moon in the cafe before us, while it pas-ses from the plane of the earth’s motion in the quarter, till itcomes again into the fame plane, has the nodes of its orbitcontinually moved backward, and the inclination of its orbitis at first diminished, viz. till it comes to Gin fig. 100, which isnear to its conjunction with the fun, but afterwards is increas-ed again almost by the fame degrees, till upon the moon’sarrival again to the plane of the earth’s motion, the inclina-tion of the orbit is restored to something more than its firstmagnitude, though the difference is not very great, becausethe points I and C are not far distant from each other \

* Vid. Nc,\t. Princ. Lib. I. prop. 66 . corolh io.

3 I. After