Sir Isaac Newton’s Book II.

204

But in other cafes the obliquity of the fun’s adion to the planeof the orbit will caufe this plane continually to change.

i 3 . Suppose in the firft place, the line, in which the twoplanes interfed each other, to be perpendicular to the linewhich joins the earth and fun. LetT (infig.98,99,100,101.)reprefent the earth; S the fun ; the plane of this fcheme theplane of the earth’s motion, in which both the fun and earthare placed. Let A C be perpendicular to S T, which joins theearth and fun; and let the line A C be that, in which the planeof the moon’s orbit interfeds the plane of the earth’s motion.To the center T deferibe in. the plane of the earth’s motionthe circle ABCD* And in the plane of the moon’s orbitdeferibe the circle AECF, one half of which AEC willbe elevated above the plane of this fcheme,, the other halfAF C as much depreffed below it.

14. Now fuppofe the moon to fet forth from the point A(in fig. 98.) in the direction of the plane AEC. Here fhewill be continually drawn out of this plane by the adion ofthe fun: for this plane AEC, if extended, will notpafs throughthe fun, but above it; fo that the fun, by drawing the moondiredly toward it felf, will force it continually more and morefrom that plane towards the plane of the earth’s motion, inwhich it felfis;Taufing it to deferibe the line AKG HI, which'will be convex to the plane AEC,. and concave to the planeof the earth’s motion. But here this power of the fun, whichis faid to draw the moon toward the plane of the earth’smotion, muft be underftood principally of fo much only of

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