And accordingly, the Line of the _Annual_ motion, (whether _Circular_ or _Elliptical_; of which I am not here to dispute,) will be described, not by the Center of the Earth (as we commonly estimate it, making the Earth a Primary and the Moon a Secondary Planet,) nor by the Center of the Moon, (as they would do, who make the Moon the Primary and the Earth a {273} Secondary Planet, against which we were before disputing:) But by the _Common Center of Gravity of the Bodies, Earth and Moon_, as one Aggregate. [Sidenote: See Fig. 2. and 3.] Now supposing A B C D E to be a part of the great Orb of the _Annual_ motion, described by the Common Center of Gravity, in so long time as from a _Full-Moon_ at A to the next _New-Moon_ at E; (which, though an Arch of a _Circle_ or _Ellipse_, whose Center we suppose at a due distance below it; yet being put about 1/25 of the whole, may well enough be here represented by a streight Line:) the Center of the Earth at T, and that of the Moon at L, must each of them (supposing their common Center of Gravity to keep the Line A E) be supposed to describe a _Periphery_ about that Common Center, as the Moon describes her Line of _Menstrual_ motion (Of which I have (in the _Scheme_) onely drawn that of the _Earth_; as being sufficient to our present purpose; parallel to which, if need be, we may suppose one described by the Moon; whose distance is also to be supposed much greater from T than in the _figure_ is expressed, or was necessary to expresse.) And in like manner E F G H I, from that _New moon_ at E, to the next _Full-moon_ at I. [Illustration] From A to E (from Full moon to New moon,) T moves (in its own _Epicycle_) upwards from the Sun: And from E to I, (from New moon to Full moon) it moves downwards, toward the Sun. Again, from C to G, (from last quarter to the following first quarter,) it moves _forwards according_ to the _Annual_ motion; But from G forward to C, (from the first Quarter to the ensuing last Quarter,) it moves _contrary_ to the _Annual_ motion. It is manifest therefore, according to this Hypothesis, that from Last quarter to First quarter (from C to G, while T is above the Line of the _Annual_ motion) its _Menstrual_ motion in its Epicycle _adds_ somewhat of Acceleration to the _Annual_ motion, and most of all at E, the New-moon: And from the first to the last quarter (from G forward to C, while T is below the Line of the _Annual_ motion,) it _abates_ of the _Annual_ motion; and most of all at I, or A the Full-moon. So that in pursuance of _Galilaeo's_ Notion, the _Menstrual_ {274} adding to or detracting from the _Annual_ motion, should either leave behinde, or cast forward, the loose waters incumbent on the Earth, (and thereby cause a Tide, or accumulation of Waters) and most of all at the Full Moon and New-moon, where those Accelerations or Retardations are greatest.