Chap. 3. PHILOSOPHY. 199

circuit it makes round the earth. This inequality of the moon’smotion about the earth is called by astronomers its variation.

id. The next effect of the fun upon the moon is, that itgives the orbit of the moon in the quarters a greater de-gree of curvature, than it would receive from the action ofthe earth alone ; and on the contrary in the conjunction andopposition the orbit is less inflected.

17. When the moon is in conjunction with the fun inthe point D, the fun attracting the moon more forcibly thanit does the earth, the moon by that means is impelled less to- /’ ■ ^

ward the earth, than otherwise it would be, and so the orbitis less incurvated ; for the power, by which the moon is im-pelled toward the earth, being that, by which it is inflected.from a rectilinear course, the less that power is, the less itwill be inflected. Again, when the moon is in the opposi-tion in B, farther removed from the fun than the earth is;it follows then, though the earth and moon are both conti-nually descending to the fun, that is, are drawn by the luntoward it self out of the place they would otherwise moveinto, yet the moon descends with less velocity than theearth ; insomuch that the moon in any given space oftime from its passing the point of opposition will haveless approached the earth, than otherwise it would havedone, that is, its orbit in relpect of the earth will ap-proach nearer to a straight line. In the last place, when *the moon is in the quarter in F, and equally distantfrom the fun as the e^rth, we observed before, that

the*

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