Poles, makes the Current to be there more conspicuous and swift, and consequently, the Eddy, or recurrent motion, nearer the Poles, where this is, more remiss:) than can easily be rendered by so small a Tumor, as he supposeth. Not to adde; that his account of the Progressive motion, which he fansieth to follow upon this Tumefaction, and by Acceleration to grow to so great a height near the Shoar (as in Chap. 13. and 14.) is a Notion, which seems to me too extravagant to be salved by any laws of Staticks. And that of the Moons motion onely Synchronizing with the Tydes, casually, without any Physical connexion; I can very hardly assent to. For it can hardly be imagined, that any such constant Synchronisme should be in Nature; but where, either the one is the cause of the other, or both depend upon some Common cause. And where we see so fair a foundation for a Physical connection. I am not prone to ascribe it to an Independent Sychronism. In sum; His History doth well enough agree with my Hypothesis; and I think, the Phænomena are much better salved by mine, than his.
And then as to Gassendus, in his discourse De Æstu Maris; I find him, after the relating of many other Opinions concerning the Cause of it, inclining to that of Galilæo, ascribing it to the Acceleration & Retardation of the Earths motion, compounded of the Annual and Diurnal; And moreover attempting to give an account of the Menstrual Periods from the Earths carrying the Moon about it self, as Jupiter doth his Satellites; which together with them is carryed about by the Sun, as one Aggregate; (and that the Earth with its Moon is to be supposed in like manner to be carried about by the Sun, as one Aggregate, cannot be reasonably doubted, by those who entertain the Copernican Hypothesis, and do allow the same of Jupiter and his Satellites.) But though he would thus have the Earth and Moon looked upon as two parts of the same moved Aggregate, yet he doth still suppose (as Galilæo had done before him) that the line of the Mean Motion of this Aggregate (or, as he calls, motus æquabilis et veluti medius) is described by the Center of the Earth (about which Center he supposeth both its own revolution to be made, and an Epicycle described by the Moons motion;) not by another Point, distinct from the Centers of both, about which, as the
common Center of Gravity, as well that of the Earth, as that of the Moon, are to describe several Epicycles. And, for that Reason fails of giving any clear account of this Menstrual Period. (And in like manner, he proposeth the Consideration as well of the Earths Aphelium and Perihelium as of the Æquinoctial and Solstitial Points, in order to the finding a Reason of the Annual Vicissitudes; but doth not fix upon any thing, in which himself can Acquiesce: And therefore leaves it in medio as he found it.)
It had been more agreeable to the Laws of Staticks, if he had, (as I do,) so considered the Earth and Moon as two parts of the same movable, (not so, as he doth, aliam in Centro et sequentem præcise revolutionem axis, aliam remotius ac velut in circumferentia, but,) so, as to make neither of them the Center, but both out of it, describing Epicycles about it: Like as, when a long stick thrown in the Air, whose one end is heavyer than the other, is whirled about, so as that the End, which did first fly foremost, becomes hindmost; the proper line of motion of this whole Body is not that, which is described by either End, but that, which is described by a middle point between them; about which point each end, in whirling, describes an Epicycle. And indeed, in the present case, it is not the Epicycle described by the Moon, but that, described by the Earth, which gives the Menstrual Vicissitudes of motion to the Water; which would, as to this, be the same, if the Earth so move, whether there were any Moon to move or not; nor would the Moons Motion, supposing the Earth to hold on its own course, any whit concern the motion of the Water.
But now, (after all our Physical, or Statical Considerations) the clearest Evidence for this Hypothesis (if it can be had) will be from Celestial Observations. As for instance; (see Fig. 5.) Supposing the Sun at S; the Earths place in its Annual Orb at T; and Mars (in opposition to the Sun, or near it) at M: From whence Mars should appear in the Zodiack at γ, and will at Full moon be seen there to be; the Moon being at C and the Earth at c; (and the like at the New-moon.) But if the Moon be in the First quarter at A, and the Earth at a: Mars will be seen, not at γ, but at α; too slow: And when the Moon is at B, and the Earth at b, Mars will be seen at β; yet too slow: till at the
Full-moon, the Moon at C, the Earth at c, Mars will be seen at γ, its true place, as if the Earth were at T. But then, after the Full, the Moon at D, the Earth at d; Mars will be seen, not at γ, but at δ, too forward: and yet more, when the Moon (at the last Quarter) is at E, the Earth at e, and Mars seen at ε. If therefore Mars (when in opposition to the Sun) be found (all other allowances being made) somewhat too backward before the Full moon, and somewhat too forward after the Full-moon, (and most of all, at the Quadratures:) it will be the best confirmation of the Hypothesis. (The like may be fitted to Mars in other positions, mutatis mutandis; and so for the other Planets.)
But this proof, is of like nature as that of the Parallaxis of the Earths Annual Orb to prove the Copernican Hypothesis. If it can be observed, it proves the Affirmative; but if it cannot be observed, it doth not convince the Negative, but only proves that the Semidiameter of the Earths Epicycle is so small as not to make any discernable Parallax. And indeed, I doubt, that will be the issue. For the Semidiameter of this Epicycle, being little more than the Semidiameter of the Earth it self, or about 1⅓ thereof (as is conjectured, in the Hypothesis, from the Magnitudes and Distances of the Earth and Moon compared;) and there having not as yet been observed any discernable Parallax of Mars, even in his neerest position to the Earth; it is very suspicious, that here it may prove so too. And whether any of the other Planets will be more favourable in this point, I cannot say.