Against. Whether there be any Vacuum? 16. On the contrary; if the fixed Stars be of a rarified and flaming Subftance, 'twill appear, that the nature of Rarity is not only a decrease of Density, but, of itself, a powerful and primary thing; no lefs than the nature of Solidity: And that it takes place both in the Air, the Æther, and the Stars themselves, so as to leave no neceffity for a Vacuum. 17. The prefent Question alfo concerning a Vacuum in the interftellar Spaces, has a dependance upon that other belonging to the Principles of Natural Philofophy; viz. Whether there be any l'acuum? But this Queftion must be put with some distinction: For 'tis one thing to deny a fimple, and another to deny a collective Vacuity; fince the reafons producible for the existence of an interfperfed Vacuity (admitting the Relaxation or Rarification of Bodies) are ftronger than thofe which make for a collective Vacuum, in the vafter Spaces. And this diftinction was not only perceived by Hero, a fubtile mechanical Philofopher; but alfo by Leucippus and Democritus, the Introducers of a Vacuum, which Ariftotle combats with certain Subtilties and turns of Wit. But the two above-mention'd acute and famous Philofophers allow an interfpers'd Vacuity; fo as to deftroy the Notion of a collective one: For, in the Opinion of Democritus, Vacuity is fo circumfcribed, that Bodies cannot be drawn afunder, any more than they can be compell'd together, beyond certain Bounds. And tho this is no where exprefly afferted in thofe Writings we have remaining of Democritusb; yet he feems to fay as much, by making Bodies infinite, as well as Space: Which he does for this Reafon, that Bodies otherwife, would never hold together; viz. if Space were infinite, and Bodies finite: And, therefore, if Matter be equally infinite with Space, Vacuity is neceffarily bound up within certain Limits: Which feems to be his true Opinion, fairly explain'd; fo as to fet certain Boundaries to the expanfion of Bodies, by the Vacuity wherewith they are coupled; without allowing any pure or fimple Vacuity, uncontained in Matter d 18. But globular Bodies, moving with equal Velocity, in Air, Water, and Quickfilver, are as the Denfities of the Fluids; (2.) that tho the Water, Air, or Quickfilver, were rarified by an infinite Subdivifion of their Parts, fo as to become Mediums infinitely fluid; they would ftill refift, after the fame manner as before: Because this Refiftance proceeds from the inactivity of Matter; which is effential to Bodies, and conftantly proportion'd to their quantity of Matter. For, tho to divide the parts of a Fluid, may leffen that Refistance which proceeds from the Friction and Tenacity of the Parts; yet the quantity of Matter is not diminished by fuch Divifion: And whilft the quantity of Matter remains the same, fo will its inactivity, to which the Refistance here understood, is ever proportional. (3.) That, therefore, to diminish this Refiitance, the quantity of Matter must be diminished in the Spaces thro which the Bodies move: Confequently, the interftellar Regions, thro which the Globes of the Planets and Comets conftantly revolve in all directions, with great freedom, are not filled with any corporeal Fluid; excepting only for fome highly rarified Vapours, and the Rays of Light tranfmitted thro thofe Regions. See Princip. Lib. II. Schol. Gen. and Lib. III. Prop. XL, &c. a See hereafter, SECT. II. 30. b See Morhof. Polyhift. Tom. II. Lib. II. Cap. VII. p. 179, &c. This is attempting to account for Cohesion in Bodies; which put into a Vacuum, fhould fall to pieces, if the Pofition were true, 4 Sir Ifaac Newton proves, that all Spaces are not equally fill'd; because, otherwise, the fpecifick Gravity of the Fluid that poffeffes the Region of the Air would be equal to that tinuous or 18. But if there be no Vacuum, after the manner of a Solution of Whether the Continuity; yet fo great a diverfity in the Parts and Regions of the Sy- Ether be conftem of Bodies, that they feem to be, as it were, of different Nations, contiguous? and Countries; there hence arifes a fecond Queftion, with regard to the connexion of the System; viz. Whether pure Ether be one uniform or continued Fluid; or whether it confifts of many contiguous Parts? By a contiguous Body we here mean a Body that lies upon another, without mixing with it. Nor do we understand fuch a hard Flooring as the common Aftronomers have feign'd; but fuch an one as may admit of flowing; as when Water floats on Quickfilver, Oil on Water, and Air on Oil. For no doubt, but in that immense tract of Æther, there are very confiderable -differences in point of Rarity and Denfity; befides many others: But this may be the Cafe, whether the parts of the Æther are continuous or contiguous. For 'tis manifeft, that even in the Sea itself, the Water on the top is not of the fame Tafte and Confiftence with that at the bottomf. And in the Atmosphere there is a great difference betwixt the Air adjacent to the Earth, and that high above it; and yet there is one entire and constant Flow in the Atmospheres. The Queftion therefore comes to this; viz. Whether the differences in the tract of Ether infinuate themselves gradually, and by a continued Flux; or whether they are conftituted, and diftributed, at certain confiderable diftances, or limits, where Bodies meet, that will not mix; as here below the Air floats on Waterh. And to take the thing fimply, that whole, pure, and limpid Body, wherein the Globes of the Earth and Planets float as in an immenfe Ocean, which in its dimenfion, and the space it poffeffes, almoft infinitely exceeds the dimenfions of those The ProceGlobes, feems to be one undivided and perfectly united thingi. dure of Na of Change to another. 19. But whoever carefully obferves Nature, will find her Method is to ture in difproceed by degrees, for certain fpaces; and then, of a fudden, to ad-ferent degrees vance by ftarts; and to use this procedure alternately: Otherwife, to con- from one Body that of Quickfilver, Gold, or any other the denfeft Bodies; which, therefore, could not defcend in Air: For no Bodies can defcend in fuch Fluids as are not fpecifically lighter than the Bodies. See Princip. Lib. III. Prop. VI. And, as the fame Philofopher fhews, there is no abfolute Vacuity in the interftellar Regions, on account of fome fubtile and highly rarified Vapour, the Rays of Light, and some fmall Refiftance, which the feveral celeftial Bodies fuftain in their Motions, his Doctrine on this Head feems fomewhat agreeable to that of Democritus, as here explained; efpecially if a fubtile elaftic Fluid, or Spirit, be fuppofed the Caufe of Gravity, or Cohesion, in Bodies. See Princip. Lib. 111. Schol. Gen. ad finem. See alfo the Queries at the end of the fame Author's Opticks. c Perhaps the finer parts of the Atmospheres of the Planets and Comets may go off into the Region of Ether, if there be any fuch Fluid, as they pafs along it; and thus, by degrees, impregnate that immenfe Ocean, and render it a kind of compound Tin&ture, as the Earth's Atmosphere more manifeftly is. See Sir Ifaac Newton's Conjecture as to the Ufe of the Comets; Princip. Lib. III. Prop. XLI. pag. 472, 473. Mr. Boyle's Memoirs for a General History of the Air. Dr. Hook's Micrographia, &c. f See Mr. Boyle on the Saltnefs of the Sea, &c. g See Mr. Boyle's Memoirs for a General History of the Air. h See the Piece last cited. Upon what experimental Foundation does this Notion of Ether ftand; as of an actual Fluid exifting in the interftellar Regions? E VOL II. fider The Heavens Parts. fider it clofely, there could be no Fabric of things; no organical Conformation, if the conftantly proceeded by infenfible degrees. This gradual Procedure, therefore, may take place in the intermundane Spaces, and not in the World itself, the Structure whereof requires very different things to be feparated, or fhut up, from, and yet approach one another. Hence, the Air immediately touches, and fucceeds to, very different Bodies from itself; viz. the Earth and Water; without going in a scale, first from Earth to Mud, and then from Mud to Water, from Water to Vapour, or Clouds, and, laftly, to Air; but Nature here jumps at once to Air, without any intermediate degreek. 20. But the moft obfervable and fundamental Divifion of all, in the divided into Air and Ether, feems derivable from the Nature, which is more or lefs three capital fufceptible of a ftellar Nature. Whence there feem to be three very remarkable kinds of Regions between the Globe of the Earth, and the utmost extent of the Heavens; viz. (1.) the Tract of Air; (2.) the Tract of the planetary Heaven1; and (3.) the Tract of the ftarry Heaven. Now the fellar Nature does not exift in the lower Tract; but in the middle one it begins; and there comes together into a few particular Globes; and in the upper diffuses itself into a very large number of Globes; fo that its top may feem to reach the entire empyrean Heaven. Procedure vens. The gradual 21. It must, however, be remember'd, according to what was just now and starting mentioned, that Nature here uses this gradual and farting Procedure by ufed by turns turns, fo as to make the Confines of the first Region communicate with in the Hea- the fecond; and thofe of the fecond with the third: For in the higher Air, after it begins to be purged of the Earth's Effluvia; and to be more rarified by the Effluvia of the celeftial Bodies; it tries and endeavours to become Flame; as in the cafe of the lower Comets m, which feem of a middle nature; between the confiftent one of the Stars, and a more perishable one. Again, the Heavens about the Sun may feem to grow ftarry, and begin to pafs into the nature of the ftellate Heaven: For the Spots which have been accurately obferved in the Sun, may poffibly be certain Rudiments of a ftarry Matter". But, in the Heavens, about Jupiter, the Stars appear in their perfection; tho, by reason of their smallness or distance, they are invisible to us, without the affiftance of Telescopes °. And again, at the greatest height of the ftarry Heaven, the ftellar Nature feems to be more continu'd, and diffus'd; from thofe numberlefs twinklings or radiations of the Æther, among the fixed Stars that are number'd P. 22. There This appears a capital Obfervation for interpreting the Works of Nature. 1 Now commonly called the Solar System. All the Comets are fhewn by Sir Ifaac Newton to be higher in the Syftem than the Moon; and to revolve in long Ellipfes about the Sun. See Princip. Lib. III. Prop. XLI. See the feveral Obfervations upon thefe Spots of the Sun in the Philofophical Transactions, French Memoirs, &c, or a Summary of the whole in Wolf. Element. Aftronom. pag. 459, 460, &c. Are any fixed Stars certainly found fo low in the Syftem as Jupiter? Thefe Twinklings are thought, by Sir Ifaac Newton, to proceed from the Refraction of our Eyes, and the tremulous Motion of the Air. See Princip. Lib. III. pag. 467. See alfo hereafter, SECT. LI. What is the 22. There is a fifth kind of Question regarding the fituation of the Question parts of the Syftem, or the Order of the Heavens. And whether there be a (5.) Syftem, with the Sun for its Centre, or no Syftem at all, fo as to leave order of the the celeftial Bodies loofe and ftraggling; or whether Aftronomers fhall Heavens? hereafter discover any new System; the Enquiry will ftill remain, what Planet is nearest to, or fartheft from, another; and, in like manner, what Planet has a greater, and what a lefs Elongation from the Earth or Sun. 23. If the Syftem of the Ancients be admitted; there appears no reafon Upon the Syfor infifting ftrenuously upon the new Enquiry, about the four fuperior fem of the Regions; viz. that of the fixed Stars, and thofe of Saturn, Jupiter, and Ancients. Mars: As their Order and Pofition have been agreed to by all Ages, without contradiction from any Phænomenon. Their respective Motions are also settled, and caufe no Error in Calculation 9. But the Ancients, even upon their own Syftem, had doubts about the Sun, Venus, Mercury, and the Moon; and the Moderns likewife have queftion'd, which was the higher Planet, Venus or Mercury. That Venus fhould be the higher is argued, because she moves fomewhat flower; and that Mercury fhould be the higher, because he seems more ty'd to the Sun; whence 'tis conceived, he must be placed the neareft to him. But for the Moon, the was always placed nearest the Earth; tho there is fome difpute about her approach to the Sun". Planets do 24. There is also another kind of Question regarding the Conftitution of Whether the the Syftem: For example, whether one Planet moves fometimes over and fome- Planes of the times under another, by turns: Which feems demonftrated in the cafe of not interfect Venus, from diligent Obfervations; whereby the has been found fometimes each other? above, and fometimes below the Sun. And 'tis proper to enquire whether the Apogee of a lower Planet may not reach the Perigée of a higher; and thus produce an Interfection of Órbits. 25. The laft Queftion, as to the fituation of the parts of the Syftem is this. Are there feveral different Centres in the Syftem; and feparate Revolutions round them? Efpecially, fince not only the Earth has been made the Centre of the firft Movement; and the Sun the Centre of the fecond; but also Jupiter is made the Centre of thofe leffer Planets, or Satellites, lately dif covered by Galilæo 3. E 2 26. And But thefe Particulars are fettled to greater Exactness by later Obfervations. See Sir Ifaac Newton, Dr. Gregory, Wolfius, &c. See thefe Particulars adjusted in Sir Ifaac Newton's Principia, Part III. De Syftemate Mundi, and from thence by the later Writers of Aftronomy; but particularly Wolfius in his Elementa Aftronomia. How the Motions of the Planets are perform'd round the Sun, without clafhing or interfering with each other, fee exhibited in a fingle Theorem, by Wolfius, in his Elementa Aftronomia, pag. 505, 506. And which Sir aac Newton demonftrates, revolve about the Centre of Jupiter, with a force reciprocally as the Squares of their Diftances from it. See Princip. Lib. III. Prop. I. And the beft Solutions of all the preceding Questions feem derivable from the fame admirable Work; but thofe who have not a fufficient ftock of Mathematicks to understand that Piece, may to good advantage confult Chrift. Wolfii Elementa Aftronomia ; where all is explain'd in a much more familiar and entertaining; yet Geometrical Manner, 26. And thus there are five capital Questions which fhould be fifted with regard to the Syftem itself; viz. (1.) Whether there be a System? (2.) What is its Centre? (3.) What its Dimenfions? (4.) What its Connexion? And, (5.) What its Order of Parts? But for the external parts of the Heavens, and the empyrean Heaven, we raise no Questions about them: For of these things there is no Hiftory nor Phenomena extant; and therefore, what is to be known of them, must be had by Confecution, not by Induction. This Enquiry, therefore, muft wait its proper time; and expect its SUITABLE METHOD. But for the immaterial Heavens, we had better trust them wholly to Religion: For what the Platonifts of old, and Patricius of late (to fhew themselves Divines in Philofophy) have faid on this Head, is mix'd with manifest Superstition, Arrogance, and Phren-fy, and, like the Icons and Eons, or Dreams and Fictions of Valentinus, bold and fruitless; so that we reject it all, as trifling, vain, and prepofterous: For to canonize Folly, as in the Apotheofis of Claudius into a MushroomGod, is intolerable: And to venerate Vanities is extreme Abomination; and the bane of the Understanding. SECT. II. PHYSICAL QUESTIONS concerning the Subftance of the CELESTIAL BODIES. The Neceffity 1. for uniting Phyficks and Aftronomy. WE E come next to the Questions regarding the Subftance of the bea-venly Bodies; into which, and the Causes of their Motions, 'tis the principal Office of Philofophy, to enquire. But Aftronomy alfo undertakes to enquire into their Motions, with the Properties thereof; and both Philofophy and Aftronomy into their Influence and Powers. There is, however, a Difference to be made betwixt Aftronomy and Philofophy: Aftronomy fhould be conceived to lay down fuch Hypotheses as best ferve the Purposes of a ready and expeditious Calculation; but Philofophy. fuch as nearly approach the Truth and Reality of Nature. Again, the Hypothefes of Aftronomy may be fubfervient to their own Convenience, but fhould in no wife prejudice the Truth of things; and the Determinations of Philofophy fhould here be perfectly explicable upon the Phenomena of Aftro nomy What kind of Intimation is this? The Method of enquiring by Induction is known, and fully explained in the Author's Novum Organum: But what is the Method of Difcovery by Confecution? Perhaps, 'tis meant, that when the Business of inductive Enquiry fhall be carried its due length, in Aftronomy; and the immenfe Regions of the fixed Stars be as well understood as the Solar Syftem, at prefent; the Notion of an empyrean Heaven may, by Confecution, appear, to future Generations, a Vanity, or a Fiction; or else all that fuppofed Region be found full of Worlds and Syftems, like the folar. But this may be launching too far, |