2. To the second objection; That, at Chatham and in the Thames, the Annual Spring-tydes, happen about the Æquinoxes; not (as this Hypothesis doth suppose elsewhere to have been observed) about the beginning of February and November. If their meaning be, that Annual High Tydes, do then happen, and then onely: If this prove true, it will ease me of half my work. For it is then easily answered, that it depends upon the Obliquity of the Zodiack; the parts of the Æquinoctial answering to equal parts of the
Zodiack, being neer the Solstitial points greatest, and near the Æquinoctial points least of all. But beside this Annual Vicissitude of the Æquinoxes, not to say, of the 4. Cardinal Points (which my Hypothesis doth allow and assert;) I believe it will be found, that there is another Annual vicissitude answering to the Suns Apogæum and Perigæum. And that the greatest Tydes of all, will be found to be upon a result of these two causes Cooperating: which (as doth the Inequality of Natural dayes, depending on these same causes) will light nearer the times, I mention. To what is said to be observed at Chatham and in the Thames, contrary to that I allege as observed in Rumney marsh: I must at present ἀπέχειν, and refer to a melius inquirendum. If those who object this contrary observation, shall, after this notice, find, upon new Observations heedfully taken, that the Spring-tydes in February and November, are not so high, as those in March and September; I shall then think the objection very considerable. But I do very well remember, that I have seen in November, very high Tydes at London, as well as in Rumney Marsh. And, the time is not yet so far past, but that it may be remembered (by your self or others then in London) whether in November last when the Tydes were so high at Dover, at Deal, at Margate, and all along the Coast from thence to Rumney Marsh, as to do in some of those places much hurt, (and, in Holland, much more;) whether, I say, there were not also at the same time, at London, (upon the Thames) very high Tydes. But a good Diary of the Height and time both of High-water, and Low-water, for a year or two together, even at Chatham, or Greenwich; but rather at some place in the open Sea, or at the Lands end in Cornwal, or on the West parts of Ireland; or at St. Hellens, or the Bermodas, &c. would do more to the resolving of this point, than any verbal discourse without it.
3. To the third Objection, That supposing the Earth and Moon to move about a Common center of gravity; if that the highest Tydes be at the New-moon, when the moon being nearest to the Sun, the Earth is farthest from it, and its compound motion at the swiftest; and that the Tydes abate as the Earth approacheth nearer; till it comes into the supposed Circle of her Annual motion: It may be demanded, why do they not still abate as the Earth comes yet nearer to the Sun; and the
swiftnesse of its compound motion still slackens? And so, why have we not Spring tides at the New Moon (when the motion is swiftest) and Neap tides at Full Moon (when the motion is slowest) but Spring tides at both? The answer (if observed) is already given in my Hypothesis it self. Because the effect is indifferently to follow, either upon a suddain Acceleration, or a suddain Retardation. (Like as a loose thing, lying on a moving body; if the body be thrust suddainly forward, that loose thing is cast back, or rather left behind, not having yet obtained an equal impetus with that of the body, on which it lyes; but if stopped, or notably retarded, that loose incumbent is thrown forward, by its formerly contracted impetus not yet qualified or accomodated to the slowness of the Body, on which it lyes.) Now both of these happening, the one at the New Moon, the other at the Full Moon, do cause high Tides at both.
4. To the fourth Objection, That the highest Tydes are not at all places, about the New Moon and Full Moon; and particularly, that, in some places of the East Indies, the Highest Tydes are at the Quadratures: I must first answer in general; That as to the particular varieties of Tydes in several parts of the World, I cannot pretend to give a satisfactory account, for want of a competent History of Tydes, &c. Because (as is intimated in what I wrote in the general) the various positions of Chanels, Bays, Promontories, Gulfs, Shallows, Currents, Trade-winds, &c. must needs make an innumerable variety of Accidents in particular places, of which no satisfactory account is to be given from the general Hypothesis (though never so true) without a due consideration of all those. Which is a task too great for me to undertake, being so ill furnished with materials for it. And then as to the particular instance of some places in the East Indies, where the highest Tydes are at the Quadratures: I suppose, it may be chiefly intended of those about Cambaia, and Pegu. At which places, beside that they are situate at the inmost parts of Vast Bayes, or Gulfs (as they are called) they have also vast In-draughts of some hundred Miles within Land; which when the Tydes are out, do lye (in a manner) quite dry: And may therefore very well be supposed to participate the effect of the Menstrual Tydes many dayes after the
cause of them happens in the open Sea, upon a like ground as in Straights and narrow Channels the Diurnall Tydes happen some hours later than in the Ocean. And a like account must be given of particular accidents in other places, from the particular situation of those places, as Bays, Chanels, Currents, &c.
5. To the 5. Objection, That the Spring-Tydes happen not, with us, just at the Full and Change, but two or three daies after. I should with the more confidence attempt an Answer, were I certain, whether it be so in the Open Seas, or onely in our Channels. For the Answers will not be the same in both cases. If onely in our Channels, where the Tydes find a large in-draught; but not in the Open Seas: we must seek the reason of it from the particular position of these places. But if it be so generally in the wide Open Seas: We must then seek a reason of it from the general Hypothesis. And, till I know the matter of Fact, I know not well, which to offer at; lest whilst I attempt to salve one, I should fall foul of the other. I know that Marriners use to speak of Spring-Tydes at the New and Full of the Moon; though I have still had a suspition that it might be some daies after, as well in the open Seas, as in our narrower Channels; (and therefore I have chosen to say, in my Papers, About the New and Full, rather than At the New and Full; and even when I do say At, I intend it in that laxer sense in which I suppose the Marriners are to be understood, for Neer that time:) Of which suspition you will find some intimations even in my first Papers: But this though I can admit; yet, because I was not sure of it, I durst not build upon it. The truth is, the Flux and Reflux of water in a vessel, by reason of the jogging of it, though it follow thereupon; yet is, for the most part, discernable some time after. For there must, upon that jog, be some time for Motion, before the Accumulation can have made a Tyde. And so I do not know but that we must allow it in all the Periods. For as the menstrual High Tyde, is not (at least with us) till some Daies after the Full and Change; so is the Diurnal High water, about as many Hours, after the Moons comming to South; (I mean, At Sea: for in Chanels it varies to all Hours, according as they are neerer or further from the open Sea:) And the Annual High-Tydes of November and February; somewhat later than
(what I conjecture to be from the same causes) the greatest Inequalities of the natural Days, happening in January and October. But this though I can admit, yet (till I am sure of the matter of Fact) I do not build upon. And since it hath hitherto been the custome to speak with that laxness of expression; assigning the times of New-moon, Full-moon, and Quadratures, with the Moons comming to South, for, what is neer those times: I did not think myself obliged in my conjectural Hypothesis (while it is yet but a Candidate) to speak more nicely. If the Hypothesis for the maine of it be found Rational; the Niceties of it are to be adjusted, in time, from particular Observation.
Having thus given you some Answers to the Objections you signifie to have been made by several persons to my Hypothesis, and that in the same order your Paper presents them to me; I shall next give you some account of the two Books, which you advised me to consult; so far as seems necessary to this business; Which, upon your intimation, I have since perused, though before I had not.
And first, as to that of Isaac Vossius, De motu Marium & Ventorum; Though I do not concur with him in his Hypothesis; That all the Great motions of the Seas, &c. should arise onely from so small a warming of the water as to raise it (where most of all) not a Foot in perpendicular, (as in his 12th Chapter.) Or that there is no other connexion between the Moons motion, and the Tydes menstrual period, than a casual Synchronism (which seems to be the doctrine of his 16th and 18th Chapters;) Beside many other things in his Philosophy, which I cannot allow: Yet I am well enough pleased with what is Historical in it, of the matter of Fact: Especially if I may be secure, that he is therein accurate and candid, not wresting the Phænomena to his own purpose. But I find nothing in it, which doth induce me to vary from my Hypothesis. For, granting his Historicals to be all true; the account of the constant Current of the Sea Westward, and of the constant Eastern Blasts, &c. within the Tropicks, is much more plausibly, and (I suppose) truly rendered by Galilæo long since, from the Earths Diurnal motion: (which, neare the Æquator, describing a greater Circle, than nearer the