Philosophical Transactions of the Royal Society Part 28

6. And that you may the less, scruple at this, I shall tell you, that even before and after Midsummer, I have found the Cold producible by our Experiment to be considerable and useful for refrigerating of Drinks, &c.

but if the Sal Armoniack be of the fittest sort (for I intimated above, that I suspected, 'tis not equally good) and if the season of the year do make no disadvantagious difference, the degree of Cold, that may be produced by no more than one pound (if not by less) of Sal Armoniack, may, within its own Sphere of Activity, be much more vehement, than, I presume, you yet imagine, and may afford us excellent Standards to adjust seal'd Weather gla.s.ses by; and for several other purposes, For I remember that in the Spring, about the end of _March_, or beginning of _April_, I was able with one pound of Sal Armoniack, and a requisite proportion of Water, to produce a degree of Cold much greater, than was necessary the preceding Winter, to make it frosty Weather abroad; nay I was able to produce real Ice in a s.p.a.ce of time, almost incredibly short. To confirm which particulars, because they will probably seem strange to you, I will here annex the Transcript of an entry, that I find in a Note book of the _Phaenomena_ and success of one of those Experiments, as I then tryed it; though I should be asham'd to expose to your perusal a thing so rudely pen'd; if I did not hope, you would consider, that 'twas hastily written onely for my own Remembrance. And that you may not stop at any thing in the immediately annext Note, or the two, that follow, it will be requisite to premise this Account of the seal'd Thermoscope; (which was a good one) wherewith these Observations were made; That the length of the Cylindrical pipe was 16. Inches; the Ball, about the bigness of a somewhat large Walnut, and the Cavity of the Pipe by guess about an eight or ninth part of an inch Diameter.

The First Experiment is thus registered. _March_ the 27th, in the Seal'd Weather gla.s.s, when first put into the Water, the tincted Spirit rested at 8-5/8 inches; being suffered to stay there a good while, and now and then stirr'd to and fro in the Water; it descended at length a little beneath 7-5/8 inches; then the _Sal Armoniack_ being put in, within about a quarter of an hour or a little more it descended to 2-11/16 inches, but before that time, in half a {260} quarter of an hour it began manifestly to freeze the vapours and drops of water on the outside of the Gla.s.s. And when the frigorifick power was arriv'd at the height, I several times found, that water, thinly plac'd on the outside, whilst the mixture within was nimbly stirr'd up and down, would freeze in a quarter of a minute (by a Minute-watch.) At about of an hour after the infrigidating Body was put in, the Thermoscope, that had been taken out a while before, and yet was risen but to the lowest freezing mark, being again put in the liquor, fell an inch beneath the mark. At about 2 houres from the first Solution of the Salt I found the tincted liquor to be in the midst between the freezing marks, whereof the one was at 5 inches (at which height when the Tincture rested, it would usually be, some, though but a small, frost abroad;) and the other at 4 inches; which was the height, to which strong and durable Frosts had reduced the liquor in the Winter. At 3 hours after the beginning of the Operation, I found not the Crimson liquor higher than the upper Freezing mark newly mention'd; after which, it continued to rise very slowly for about an hour longer; beyond which time I had not occasion to observe it.

Thus far the _Note-book_; wherein there is mention made of a Circ.u.mstance of some former Experiments of the like kind, which I remember was very conspicuous in this newly recited. For, the frigorifick mixture having been made in a Gla.s.s body (as they call it) with a large and flattish bottom, a quant.i.ty of water, which I (purposely) spilt upon the Table, was by the operation of the mixture within the Gla.s.s, made to freeze, and that strongly enough, the bottom of the Cucurbite to the Table; that stagnant liquor being turn'd into solid ice, that continued a considerable while unthaw'd away, and was in some places about the thickness of a half Crown piece.

Another Observation, made the same Spring, but less solemn, as meant chiefly to shew the Duration of Cold in a high degree, is recorded in these terms: The first time, the Seal'd Weather-gla.s.s was put in, before it touch'd the common water, it stood at 8-1/8, having been left there a considerable while, and once or twice agitated the water, the tincted liquor sunk but to 7-7/8, or at furthest, 7-6/8; then the frigorifick liquor being put into the water with circ.u.mstances disadvantagious enough in (about) half a quarter of an hour the tincted liquor fell beneath 3, and the Thermoscope, being taken out, and then put in again, an hour after the water had been first infrigidated subsided beneath 5 inches, and consequently within of an inch of the mark of the strongly freezing weather.

7. Whereas the grand thing, that is like to keep this Experiment from being as generally _Useful_, as perhaps it will prove _Luciferous_, is the Dearness of Sal Armoniack, two things may be offered to lessen this Inconvenience. For _first_, Sal Armoniack might be made much cheaper, if instead of fetching it beyond-sea, our Country-men made it here at home; (which it may easily be and I am ready to give you the Receipt, which is no great Secret.) But _next_, I considered, that probably the infrigidating vertue of our mixture might depend upon the peculiar Texture of the Sal Armoniack whereby, whilest the Water is dissolving it, either some Frigorifick particles are extricated and excited or (rather) some particles which did before more agitate the minute parts of the water, are expell'd (or invited out by the ambient Bodies) or {261} come to be clogg'd in their motion: Whence it seem'd reasonable to expect that upon the Reunion of the Saline particles into such a Body, as they had const.i.tuted before, the redintegrated Sal Armoniack having, neer upon, the same Texture, would, upon its being redissolv'd, produce the same, or a not much inferior degree of Coldness: And hereupon, though I well enough foresaw that an Armoniack solution, being boyl'd up in Earthen vessels (for Gla.s.s ones are too chargeable) would, by piercing them, both lose some of the more subtle parts, and thereby somewhat impaire the texture of the rest; yet I was not deceiv'd in Expecting, that the dry Salt, remaining in the pipkins, being redissolv'd in a due proportion of water, would very considerably infrigidate it; as may further appear by the Notes, which for your greater satisfaction you will find here subjoyn'd, as soon as I have told you, that, though for want of other vessels I was first reduc'd to make use of Earthen ones, and the rather, because some Metallin Vessels will be injur'd by the dissolv'd Sal Armoniack, if it be boyl'd in them; yet I afterwards found some conveniencies in Vessels of other Mettall, as of Iron; whereof you may command a further Account.

_March_ the 29th, the Thermoscope in the Air was at 8-7/8 inches; being put into a somewhat large evaporating gla.s.s, fill'd with water, it fell (after it staid a pretty while, and had been agitated in the liquor) to 8. inches: then about half the Salt, or less, that had been used _twice_ before, and felt much less cold than the water, being put in and stirr'd about, the tincted Spirit subsided with a visible progress, till it was faln manifestly beneath 4. inches; and then, having caused some water to be freshly pump'd and brought in; though the newly mention'd Solution were mixt with it, yet it presently made the Spirit of Wine manifestly to ascend in the Instrument, much faster, than one would have expected, &c.

And this much may suffice for this time concerning our _Frigorifick_ Experiment; which I scarce doubt but the _Cartesians_ will lay hold on as very favourable to some of their Tenents; which you will easily believe, it is _not_ to the Opinion, I have elsewhere oppos'd, of those Modern Philosophers, that would have _Salt-petre_ to be the _Primum Frigidum_: (though I found by trial, that, whilst 'tis actually dissolving, it gives a much considerabler degree of Cold, than otherwise.) But about the Reflexions, that may be made on this Experiment, and the Variations, and Improvements & Uses of it, though I have divers things lying by me; yet, since you have seen several of them already, and may command a sight of the rest, I shall forbear the mention of them here, not thinking it proper, to swell the bulk of this Letter with them.

_An Account of two Books lately printed in London._

I. _EUCLIDIS ELEMENTA GEOMETRICA, novo ordine ac methodo demonstrata._ In this compendious and pretty Edition, the Anonymous Author pretends to have rendred these Elements more expeditious; by bringing all together into one place, what belongs to one and the same subject: Comprising 1. what _Euclid_ hath said of _Lines_, Streight, Intersecting one another, and Parallel. 2. What he hath demonstrated of a _Single Triangle_, and of _Triangles Compared_ one with another. 3. What of the _Circle_, and its Properties. 4. What of _Proportions_ in Triangles and other Figures. 5.

What of _Quadrats_ and _Rectangles_, made of Lines diversly {262} cut. 6.

What of _Plane Superficies_'s. 7. What of _Solids_. After which follow the _Problems_. The _Definitions_ are put to each _Chapter_ as need requireth.

The _Axioms_, because they are few, and almost every where necessary, are not thus distributed in _Chapters_. The _Postulata_, are not subjoyn'd to the _Axioms_, but reserv'd for the _Problems_, the Author esteeming, that they being _practical_ Principles, had only place in _Problems_.

This for the _Order:_ As to the _Manner_ of Demonstrating, One and the same is observ'd in most Propositions; all with much brevity; to the end, that what is not of it self difficult, may not be made so, by mult.i.tude of Words and Letters.

II. _THE ENGLISH VINE-YARD VINDICATED._ The Author (Mr. _John Rose_, his Majesties Gardener at his Royal Garden in St. _James_'s) makes it his business in this small Tract (a very thin Pocket-book) by a few short Observations made by himself, to direct _Englishmen_ in the _Choice_ of the _Fruit_, and the _Planting_ of Vine-yards; heretofore very frequently cultivated, though of late almost quite neglected by them.

He discourses skilfully, 1. Of the _severall sorts_ of _Vines_, and what _Grapes_ are most sutable to the _Climate_ of _England_; where he chiefly commends the small _Black-grape_, or _Cl.u.s.ter-grape_; the _Parsley-grape_; the White _Muscadine_; the _Frontiniack_; and a new _White-grape_, with a red Wood and a dark green Leaf: All these being early ripe fruit. 2. Of the _Soyle_, and _Scituation_ of a Vine-yard in _England_: Where, as to the _First_, he pitches upon a _Light Soile_, having a bottom of _Chalk_ or _Gravel_, and given to _Brambles_ observing, that no Plant whatsoever is so connatural to the Vine for Soyl, as the _Bramble_. As for the _Scituation_ he chooses that side or declivity of a Hill, that lies to the _South_ or _Southwest_; and is favoured with _other Hills_ somewhat higher, or _Woods_ on the _North_ and _East_, to break the rigour of those quarters. This direction he thinks of that importance, that he affirms, that the discouragement of the Culture of Vines in _England_ has only proceeded from men's misinformation on this material article of _Choice_ of _Soyle_ and _Scituation_. 3. How to _prepare_ the Ground for the Plantation, _vid._ by plowing up the _Swarth_ in _July_, and by disposing the _Turf_ in _small_ heaps, and so burning them, and spreading the ashes over the Land; care being taken, that by heaping too much materials together, the Earth be not over-burnt by the excessive heat and fire, which they require to reduce them to ashes.

What is added, of the Manner of planting the _Sets_; of Dressing, Pruning, and Governing the Plantation; of the Ordering and Cultivating the Vine-yard after the first four years, till it needs renewing; as also of the _manner_ and _time_, how and when to manure the Vine-yard, with Compost, will be better understood from the Book it self, than can be here described; the Author pretending, that, those few observations of his, as the native production of his own Experience, being practised with care, the Vine-yards in _England_ may be planted, govern'd and perpetuated with undoubted success; and offering withall to furnish those, that have a desire to renew this Culture, and to store their grounds with _Sets_ and _Plants_ of all those sorts, which he recommends; he having a plentiful _stock_ of them all.

Printed with Licence for _John Martyn_, and _James Allestry_, Printers to the Royal Society. 1666.

{263}

_Num._ 16.

PHILOSOPHICAL _TRANSACTIONS._

_Munday_, _August_ 6. 1666.

The Contents.

_An essay of Dr. _John Wallis_, exhibiting his _Hypothesis_ about the _Flux and Reflux of the Sea_, taken from the consideration of the _Common Center of Gravity of the Earth and Moon_; together with an _Appendix_ of the same, containing an _Answer_ to some _Objections_, made by severall Persons against that _Hypothesis_. Some Animadversions of the same _Author_ upon Master _Hobs'_s late Book, _De Principiis & Ratiocinatione Geometrarum_._

_An Essay of Dr. _John Wallis_, exhibiting his _Hypothesis_ about the _Flux and Reflux of the Sea_._

How abstruse a subject in Philosophy, the _Flux and Reflux of the Sea_ hath proved hitherto, and how much the same hath in all Ages perplexed the Minds even of the best of _Naturalists_, when they have attempted to render an Account of the Cause thereof, is needless here to represent. It may perhaps be to more purpose, to take notice, that all the deficiencies, found in the _Theories_ or _Hypotheses_, formerly invented for that End, have not been able to deterre the Ingenious of _this_ Age from making farther search into that Matter: Among whom that Eminent Mathematician Dr. _John Wallis_, following his happy _Genius_ for advancing reall Philosophy, hath made it a part of his later Inquiries and Studies, to contrive and deduce a certain Hypothesis concerning that _Phaenomenon_, taken {264} from the Consideration of the _Common Center of Gravity of the Earth and Moon_, This being by several Learned Men lookt upon, as a very rational Notion, it was thought fit to offer it by the Press to the Publick, that other Intelligent Persons also might the more conveniently and at their leisure examine the _Conjecture_ (the Author, such is his Modesty, presenting it no otherwise) and thereupon give in their sense, and what Difficulties may occur to them about it, that so it may be either confirm'd or laid aside accordingly; As the _Proposer_ himself expressly desires in the Discourse, we now, without any more _Preamble_, are going to subjoyn, as it was by him addressed, by way of Letter, from _Oxford_ to Mr. _Boyle, April_ 25. 1666. and afterwards communicated to the _R. Society_, as follows:

You were earnest with me, when you last went from hence, that I would put in writing somewhat of that, which at divers times, these three or four years last past, I have been discoursing with your self and others concerning the _Common Center of Gravity of the Earth and Moon_, in order to salving the _Phaenomena_ as well of the _Seas Ebbing and Flowing_; as of some perplexities in _Astronomical Observations_ of the _Places_ of the Celestial Bodies.

How much the World, and the great Bodies therein, are manag'd according to the _Laws of Motion_, and _Statick Principles_, and with how much more of clearness and satisfaction, many of the more abstruse _Phaenomena_ have been salved on such Principles, within this last Century of years, than formerly they had been; I need not discourse to you, who are well versed in it. For, since that _Galilaeo_ and (after him) _Torricellio_, and others, have applied _Mechanick_ Principles to the salving of _Philosophical_ Difficulties; _Natural Philosophy_ is well known to have been rendered more intelligible, and to have made a much greater progress in less than an hundred years, than before for many ages.

The _Seas Ebbing and Flowing_, hath so great a connexion with the _Moons_ motion, that in a manner all Philosophers (whatever other Causes they have joyned with it), have attributed much of its cause to the _Moon_, which either by some _occult quality_, {265} or _particular influence_, which it hath on moyst Bodies, or by some _Magnetick vertue_, drawing the water towards it, (which should therefore make the Water there _highest_, where the Moon is _vertical_) or by its gravity and pressure downwards upon the Terraqueous Globe (which would make it _lowest_ where the Moon is _vertical_) or by whatever other means (according to the several Conjectures of inquisitive persons,) hath so great an influence on, or at least a connexion with, the Sea's Flux and Reflux, that it would seem very unreasonable, to seclude the consideration of the Moons motion from that of the Sea: The _Periods of Tides_ (to say nothing of the greatness of them near the New moon and Full moon) so constantly waiting on the Moon's motion, that it may be well presumed, that either the one is governed by the other, or at least both from some common cause.

But the first that I know of, who took in the consideration of the _Earth's_ motion, (_Diurnal_ and _Annual_) was _Galilaeo_; who in his _Systeme of the World_, hath a particular discourse on this subject: Which, from the first time I ever read it, seemed to me so very rational, that I could never be of other opinion, but that the true Account of this great _Phaenomenon_ was to be referred to the Earths motion, as the _Princ.i.p.al_ cause of it: Yet that of the Moon (for the reasons above mentioned) not to be excluded, as to the determining the _Periods of Tides_, and other circ.u.mstances concerning them. And though it be manifest enough, that _Galilaeo_, as to some particulars, was mistaken in the account which there he gives of it; yet that may be very well allowed, without any blemish to so deserving a person, or prejudice to the _main Hypothesis_: For that Discourse is to be looked upon onely as an _Essay_ of the _general Hypothesis_; which as to _particulars_ was to afterwards adjusted, from a good _General History of Tides_; which it's manifest enough that he had not; and which is in a great measure yet wanting. For were the matter of Fact well agreed on, it is not likely, that several Hypotheses should so far differ, as that one should make the Water _then_ and _there_ at the Highest, _where_ and _when_ the other makes it at the Lowest; as when the Moon is Vertical to the place. {266}

And what I say of _Galilaeo_, I must in like manner desire to be understood of what I am now ready to say to you. For I do not profess to be so well skilled in the History of Tides, as that I will undertake presently to accommodate my _general Hypothesis_ to the _particular cases_; or that I will indeed undertake for the certainty of it, but onely as an _Essay_ propose it to further consideration; to stand or fall, as it shall be found to answer matter of Fact. And truly had not your importunity (which is to me a great Command) required me to do it, I should not so easily have drawn up any thing about it, till I had first satisfied my selfe, how well the Hypothesis would answer Observation: Having for divers years neglected to do it, waiting a time when I might be at leisure throughly to prosecute this design.

But there be two reasons, by which you have prevailed with me, at least to do something. _First_, because it is the common Fate of the _English_, that out of a modesty, they forbear to publish their Discoveries, till prosecuted to some good degree of certainty and perfection; yet are not so wary, but that they discourse of them freely enough to one another, and even to Strangers upon occasion; whereby others, who are more hasty and venturous, comming to hear of the notion, presently publish something of it, and would be reputed thereupon, to be the first Inventers thereof: though even that little, which they can then say of it, be perhaps much less, and more imperfect, than what the true Authors could have published long before, and what they had really made known (publikely enough, though not in print) to many others. As is well known amongst us as to the business of the _Lymphatick Vessels_ in _Anatomy_; the _Injection of Liquors into the veins of Living animals_; the _Exhibiting of a straight line equal to a crooked_; the _spot in Jupiter_, whence his motion about his own Axis may be demonstrated; and many other the like considerable Inventions.

The _other_ Reason (which, with me, is more really of weight, though even the former be not cotemptible) is, because, as I have been already for at least three or four years last past diverted from prosecuting the inquiry or perfecting the Hypothesis, as I had thoughts to do; so I do not know, but like Emergencies may divert me longer; and whether I shall ever so {267} do it, as to bring it to perfection, I cannot determine. And therefore, if as to my self any thing should _humanitus accidere_; yet possibly the notion may prove worth the preserving to be prosecuted by others, if I do it not. And therefore I shall, at least to your self, give some general account of my present imperfect and undigested thoughts.

I consider therefore, that in the Tides, or the Flux and Reflux of the Sea, besides extraordinary Extravagancies or Irregularities, whence great Inundations or strangly high Tides do follow, (which yet perhaps may prove not to be so meerly accidental as they have been thought to be, but might from the regular Laws of Motion, if well considered, be both well accounted for and even foretold;) There are these _three_ notorious Observations made of the Reciprocation of Tides. _First_, the _Diurnal_ Reciprocation; whereby twice in somewhat more than 24. hours, we have a Floud and an Ebbe; or a High-water and Low-water. _Secondly_, the _Menstrual_; whereby in one _Synodical_ period of the Moon, suppose from Full-moon to Full-moon, the Time of those Diurnal Vicissitudes doth move round through the whole compa.s.s of the [Greek: Nuchthemeron], or Natural day of twenty four hours: As for instance, if at the Full-moon the full Sea be at such or such a place just at Noon, it shall be the next day (at the same place) somewhat before One of the clock; the day following, between One and Two; and so onward, till at the New moon it shall be at midnight; (the other Tide, which in the Full moon was at midnight, now at the New-moon coming to be at noon;) And so forward till at the next Full-moon, the Full sea shall (at the same place) come to be at Noon again: Again, That of the Spring-tides and Neap-tides (as they are called;) about the Full-moon and New-moon the Tides are at the Highest, at the Quadratures the Tides are at the Lowest: And at the times intermediate, proportionably. _Thirdly_, the _Annual_; whereby it is observed, that at sometimes of the year, the Spring-tides are yet much higher than the Spring-tides at other times of the year: Which Times are usually taken to be at the Spring and Autumne; or the two aequinoxes; but I have reason to believe (as well from my own Observations, for many years, as of others who have been {268} much concerned to heed it, whereof more will be said by and by;) that we should rather a.s.sign the beginnings of _February_ and _November_, than the two _aequinoxes_.

Now in order to the giving account of these three Periods, according to the _Laws of Motion_ and _Mechanick Principles_; We shall _first_ take for granted, what is now adayes pretty commonly entertained by those, who treat of such matters; _That a Body in motion is apt to continue its motion, and that in the same degree of celerity, unless hindred by some contrary Impediment_; (like as a Body at rest, to continue so, unless by some sufficient mover, put into motion:) And accordingly (which daily experience testifies) if on a Board or Table, some loose inc.u.mbent weight, be for some time moved, & have thereby contracted an _Impetus_ to motion at such a rate; if that Board or Table chance by some external obstacle, or otherwise, to be stopped or considerably r.e.t.a.r.ded in its motion, the inc.u.mbent loose Body will shoot forward upon it: And contrarywise, in case that Board or Table chance to be accelerated or put forward with a considerably greater speed than before, the loose inc.u.mbent Body, (not having yet obtained an equal _Impetus_ with it) will be left behind, or seem to fly backward upon it. Or, (which is _Galilaeo_'s instance,) if a broad Vessel of Water, for some time evenly carried forward with the water in it, chance to meet with a stop, or to slack its motion, the Water will dash forward and rise higher at the fore part of the Vessel: And, contrarywise, if the Vessel be suddenly put forward faster than before; the Water will dash backwards, and rise at the hinder part of the Vessel. So that an Acceleration or r.e.t.a.r.dation of the Vessel, which carries it, will cause a rising of the Water in one part, and a falling in another: (which yet, by its own weight, will again be reduced to a Level as it was before.) And consequently, supposing the Sea to be but as a loose Body, carried about with the Earth, but not so united with it, as necessarily to receive the same degree of _Impetus_ with it, as its fixed parts do: The acceleration or r.e.t.a.r.dation in the motion of this or that part of the Earth, will cause (more or less, according to the proportion of it) such a das.h.i.+ng of the Water, or rising at one part, with a Falling at another, as is that, which we call the Flux and Reflux of the Sea. {269}

[Ill.u.s.tration]

Now this premised, We are next, with him, to suppose the Earth carried about with a double motion; The one _Annual_, as (_Fig._ 1.) in B E C the great Orb, in which the Center of the Earth B, is supposed to move about the Sun A.

The other _Diurnal_, whereby the whole moves upon its own _Axis_, and each point in its surface describes a Circle, as D E F G.

It is then manifest, that if we suppose, that the Earth moved but by any one of these motions, and that regularly, (with an equal swiftness;) the Water, having once attained an equal _Impetus_ thereunto, would still hold equal pace with it; there being no occasion, from the Quickening or Slackening of the Earths motion, (in that part where the Water lyeth) for the Water thereon either to be cast Forward or fall Backward; and thereby to acc.u.mulate on the other parts of the Water: But the true motion of each part of the Earths surface being compounded of those two motions, the _Annual_ and _Diurnal_; (the _Annual_ in B E C being, as _Galilaeo_ there supposeth, about three times as fast as a _diurnal_ motion in a great Circle, as D E F;) while a Point in the Earths surface moves about its Center B. from G. to D. and E. and at the same time, its Center B. be carried forwards to C; the true motion of that Point forwards, is made up of both those motions; to wit, of B to C, and of G to E; but while G moves by D to E, E moves backward by F to G, contrary to the motion of B to C; so that the true motion of E, is but the difference of B C, and E G: (for, beside the motion of B above the Center; G. is also put forward as much as from G to E; and E put backward as much as from E to G:) so that the _Diurnal_ motion, in that part of the Earth, which is next the Sun, as E F G, doth abate the progress of the _Annual_, (and most of all at F;) and in the other part, which is from the Sun, as G D E, it doth increase it, (and most of all at D.) that is, in the day time there is abated, in the night time is added to the _Annual_ motion, about as much as is G E, the Earths _Diameter_. Which would afford us a Cause of two Tides in twenty four hours; the One upon the greatest Acceleration of motion, the Other upon its greatest r.e.t.a.r.dation.

And thus far _Galilaeo_'s Discourse holds well enough; But then {270} in this it comes short; that as it gives an Account of two Tides; so those two Tides are alwayes to be at F and D; that is, at _Noon_ and _Midnight_; whereas Experience tells us, that the Time of Tides, moves in a _moneths s.p.a.ce_ through all the 24. hours. Of which he gives us no account. For though he do take notice of a Menstrual Period; yet he doth it onely as to the _Quant.i.ty_ of the Tides; greater or less; not as to the _Time_ of the _Tides_, sooner or later.

[Sidenote: * _Vid. Riccioli Almagest. novum_, Tom. 1, lib. 4. cap. 10. n.

111. pag. 216. 2.]

To help this, there is one (_Vid.* Jo. Baptista Balia.n.u.s_) who makes the _Earth_ to be but a _secondary_ Planet; and to move, not directly about the Sun, but about the Moon, the Moon meanwhile moving about the Sun; in like manner as we suppose the Earth to move about the Sun, and the Moon about it.

But this, though it might furnish us with the foundation of a _Menstrual_ Period of Accelerations and r.e.t.a.r.dations in the compound motion of several parts of the Earths surface; yet I am not at all inclined to admit this as a _true Hypothesis_, for divers Reasons, which if not demonstrative, are yet so consonant to the general Systeme of the World, as that we have no good ground to disbelieve them. For 1. The Earth being undeniably the greater Body of the two (whereof there is no doubt to be made) it cannot be thought probable, that this should be carried about by the Moon, lesser than it self: The contrary being seen, not onely in the _Sun_, which is bigger than any of the Planets, which it carryes about; but in _Jupiter_, bigger than any of his _Satellites_; and _Saturne_, bigger than his. 2. As the _Sun_ by it's motion about it's own Axis, is with good reason judged to be the _Physical_ cause of the _Primary_ Planets moving about it; So there is the like reason to believe, that _Jupiter_ and _Saturne_ moving about their Axes, are the Physical cause of their _Satellites_ moving about them, which motion of _Jupiter_ hath been of late discover'd, by the help of a _fixed_ Spot discern'd in him; and we have reason to believe the like of _Saturne:_ Whether _Venus_ and _Mercury_ (about whom no _Satellites_ have been yet observed) be likewise so moved; we have not yet the like ground to determine: But we have of _Mars_; from {271} the Observations of Mr. _Hook_ made in _February_ and _March_ last, and by him communicated to the _Royal Society_, and since Printed in the _Transactions_, published _Apr._ 2.