Chap. 3'. PHILOSOPHY. 193

planets being fometimes nearer to the fun than the pri-mary, and fometimes more remote, they are not alwaya&ed upon in the fame degree with their primary, butwhen nearer to the fun, are attracted more, and when far-ther diftant, are attracted lefs. Hence arife various inequali-ties in the motion of the fecondary planets a .

9. Some of thefe inequalities would take place, thoughthe moon, if undifturbed by the fun, would have moved ina circle concentrical to the earth, and in the plane of the earth’sMotion ; others depend on the elliptical figure, and the ob-lique lituation of the moon’s orbit. One of the firfl kind is,that the moon is caufed fo to move, as not to defcribe equalfpaces in equal times, but is continually accelerated, as fhepaffes from the quarter to the new or full, and is retardeda gain by the like degrees in returning from the new and fullto the next quarter. Here we confider not fo much the ab-solute, as the apparent motion of the moon in refpedt to us.

10 . The principles of aftronomy teach how to diflin-guifh thefe two motions. Let s (in fig. 95-.) reprefent theSun, A the earth moving in its orbit BC, DEFG the moon’s° r hit, the place of the moon H. Suppofe the earth to have^oved from A to I. Becaufe it has been fhewn, that the^oon partakes of all the progreflive motion of the earth ; andlikewife that the fun attra&s both the earth and moon equal-h» when they are at the fame diftance from it, or that the^an a&ion of the fun upon the moon is equal to its adtion

* Newton’s Princ. philof. Lib. III. prop, zz, 23,

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