Stars, is not fo perfectly determined, for want of Certainty in their Parallaxes. Alfo in the Copernican Syftem the Distance varieth, not only from the Motion of the Planets; but also from the Motion of the Earth itself. THE Reason for either Opinion, (viz. of the Ptolemaic and Copernican) about the Situation of the Earth, are much the fame with those we difcuffed in the preceeding Chapter about the Earth's Motion. For this Difpute is of great Affinity with the former. Because, if the Sun hath an annual Motion, then the Earth and not the Sun poffeffes the middle Place: But if the Earth fo move, the Sun and not the Earth will certainly be in the Center. THE following Arguments favour the Copernican Hypothefis. 1. THE Sun is not only the glorious Fountain of Light, which like a clear fhining Torch, illuminates the Earth, Moon, Venus, and, without doubt, the rest of the Planets; but is alfo the Focus of Heat, and the Source of vital Spirits; whereby the whole Univerfe is fubfifted and nourished: and therefore very probably poffeffeth the Center about which they all revolve. 2, IT is more likely that the Earth, with the reft of the Planets, should revolve bout the Sun, when they receive Light and Heat from him; than that the Sun fhould move about the Earth, when he receives nothing from it. 3. THERE are many Caufes why the Sun fhould poffefs the middle Place, and the reft of the Planets revolve round him, (efpecially if we embrace the Hypothefis of Kepler concerning the Motion of the Planets) the chief of which is, that the Sun, being a vaft Body, is moved about it's Axis, and by a strong [Vectory] Force exciteth the 2 Earth Earth and the reft of the Planets to a circular Mo tion (c). 4. THIS Rotation of the Sun about it's Axis is proved from the Obfervations of the Spots upon it's Surface by Galileo (d), Scheiner, &c. and we may reasonably prefume, it is owing to this common Cause that the reft of the Planets revolve about theirs; but we cannot perceive a likelihood of any Motion in this Luminary (e). (c) The fagacious Kepler was the Founder of the New*tonian Philofophy: it was he that first found out the true Syftem of the World, and the Laws which the celeftial Bodies obferve in their Motions; it was he that determined the true Path of the Earth, and the reft of the Planets about the Sun, and difcovered the harmonic Proportions and Concinnities of their Distances and Motions and tho' he did not demonftrate (and fhew a Reafon for the neceffity of) fuch Laws and Proportions; yet he gave a Hint, and laid a Foundation for that Prince of Geometers Sir ISAAC NEWTON, to demonftrate an abfolute Neceffity of thefe Laws; and that without a total Subverfion of the Laws of Nature, no other Rule could take Place in the Revolutions of the heavenly Bodies. (d) He was the first that applied a Telescope to the Heavens, and by it's means difcovered a great may new furprifing Phænomena; as the Moons or Satellites of Jupiter, and their Motions; the various VOL. I. 5. IF Phafes of Saturn; the Increase and Decrease of the Light of Venus; the mountainous and uncertain Surface of the Moon; the Spots of the Sun; and the Revolution of the Sun about it's own Axis: all which were first discovered and obferved by this great Philofopher. Keill's Aftron. Lect. Pref. Pag. 11. (e) From the later Obfervations of Aftronomers it is manifeft to our Sight, that alfo every Heavenly Body we have any good Views of, is turned round fome principal Point, and alfo it's own Axis, viz. hath the like Annual Revolutions, and Diurnal Motions as thofe are which we afcribe to the Earth; yea even the more maffy Globes of Saturn and Jupiter, which seem not in their own Nature more fitted for fuch Rotations. Wherefore we may certainly conclude, that it is as poffible, and as probable, that this our leffer Globe, fhould perform it's Revolutions according to the fame Law which is obferved in the rest of the Planets, whereby the beautiful Order and Harmony of Motions is 5. IF we fuppofe the Earth placed betwixt Mars and Venus, and alfo place the Sun in the Center of the System; the Motion of each of the Planets will be exactly in Proportion to their feveral Distances from that Center: But this will not hold in the Ptolemaic Hypothefis, as is manifest by comparing the Motion of the Sun, Venus, Mercury, &c. (f). 6. THE Celestial Phænomena, mentioned in the former Chapter, to prove the annual Motion of the.. Earth, do likewife as effectually prove that this is the right Place in which it ought to be moved, viz. The Retrograde Motion, and feeming Immobility of the Planets; the admirable apparent Motion [and Phafes] of Venus and Mercury, &c (g). For fince the annual Motion of the Earth is prefuppofed in this Place, or in fome other very near it ; every where preserved thro' the Frame of Nature. (f) Sir Ifaac Newton's Demonftration, That the Squares of the Planets Revolutions are as the Cubes of their Diftances, every where takes Place, if the Sun be fuppofed the Center of the Planets about him; but does not hold at all in Relation to the Earth; for if the Moon revolve round the Earth in (27 Days) a Perio'dical Month, as it certainly does, the Sun, as being at a greater Distance, will take no less than 54700 Years, according to the aforefaid Law, to make his Revolution about the Earth. But fince this Law, is found to be obferved not only in the primary Planets about the Sun, but alfo in the Secondaries a bout Jupiter, Saturn, and the Earth, it is an inconteftable Ar2 gument that the Sun is as much the Center of the Earth and Planets about him, as the Earth is of the Moon. (g) Thefe Obfervations, which utterly overthrow the Ptolemaic Hypothefis, are owing to later Aftronomers. For they, by their Glaffes, have found out that the spherical Figure of Venus and Mercury, feen from the Earth, will be altered, and have the fame variety of Phases as the Moon hath, viz. will appear opake, horned, bifected, gibbous, and full, at proper Distances from the Sun, as explained upon the Copernican Hypothefis; which certainly establishes and confirms that Order and Situation, namely that Venus and Mercury revolve about the Sun in Orbits that are included within the Earth's Orbit. this. this Argument, in my Opinion, is the best to defend it by; fince this fituation of the Earth cannot be proved immediately from it's diurnal Motion! Because it might poffefs the Center of the Universe, and have a diurnal Motion, tho' it wanted the an nual; as Origanus fuppofed. 7. BY this Hypothefis likewife, the Variation of the Distances of the Planets from the Earth is accounted for. I. THE Ptolemaics, on the other hand, oppose the Pythagorean Opinion, and endeavour to prove that the True Place of the Earth is in the Center of the World, by the following Arguments. That heavy Bodies are all naturally carried towards the Center; but that the Earth is more ponderous than the reft, therefore it ought to refide in the Center (b). 2. Heavy Bodies would recede from the Earth towards the Center of the World, if the Earth itself was not in the Center. 3. The Center is the baseft Place, and the Earth the ignobleft Part of the Creation; therefore it ought to be placed in the Center. 4. If the Earth was placed out of the Center of the World, and was not the Center of the Stars and Planets Motion, then would the Stars and Conftellations at fome Seasons of the Year appear greater than at others (i). 5. The Medium of the Heavens could not always be percep tible, nor would Taurus rife when Scorpio fets. 6. Neither would there be Equinoxes. 7. Nor would the Moon fet, nor be eclipfed when the Sun was rifing. 8. Neither could an equal Number of (b) This Affertion is falfe: See the Note at the end of this Chapter (i) Tho' this does not hold in the fixed Stars, because of their immenfe Distance; yet all the fuperior Planets feem G far greater in the middle of 2 SECT. II. Miles on the Earth answer to each Degree in the Heavens. THE Copernicans eafily refute these Arguments of the Ariftotelians. For the first and fecond is rejected, because the Motion of heavy Bodies is not towards the Center of the Universe, but towards the Earth, a homogeneous Body; as is proved from the Parts of the Sun and Moon, and of the Loadftone. In the third both the Affumptions are falfe; For the Center is an Honourable Place; and the Earth is no ways difhonourable. The rest of the Arguments are eafily difproved by a Defcription of the System; it being first prefuppofed that tho' the Earth's Distance from the Sun be very great, yet if compared with the Distance of the fixed Stars, it is fo fmall, that it hath no Proportion to it; which feems to fome a great Poftulatum in the Copernican Aftronomy (k). (k) To find this Variation of the Distance of the fixed Stars (arifing from the annual Motion of the Earth, and called their annual Parallax) hath been often attempted by the Copernican Aftronomers; because that the annual Motion of the Earth would thereby be not only made probable, but certainly demonftrated. This, I fay, was attempted without Succefs, 'till Dr Hook and Mr Flamfeed, by new invented accurate Inftruments, feemed to have found out this annual Parallax to be at leaft as much again as the double of the Sun's diurnal Parallax, viz. 47 Seconds. But Mr Molyneaux and Mr Bradley, by their late accurate Obfervatiens, could not, with all their Skill, determine any fenfible Parallax at all (only they difcovered a feeming new Motion of the fixed Stars, which (allowing the progreffive Motion of Light) does in fome Meafure demonftrate the annual Motion of the Earth). There appearing therefore, after all, no fenfible Parallax in the fixed Stars, the Anti-Copernicans have still room, on that Account, to object against the Motion of the Earth. And the Copernicans are still obliged to hold, that the Orbis_Magnus is but as a Point in Comparifon of the Distance of the neareft fixed Stars; which is certainly (as our Author obferveth) a great Blot in the Copernican Aftronomy, left to be wiped out by future Ages. |