PROP. I.

The Diurnal Motion, or that which occafions the Revolution of Day and Night, and the apparent rifing and fetting of the Sun, Moon, and Stars, in the Space of 24 Hours, which we call a Day, belongs to the Earth, and not to the Heavens.

DEMONSTRATION.

(1.) All the Phænomena or Appearances relating to this Matter, are now certainly known to be equally natural and neceffary Confequences of a diurnal Revolution of the Earth from Weft to Eaft, as of the like Revolution of the whole Syftem of the Heavens from East to West; as thofe who have apply'd themfelves to this part of Aftronomy do well know: Juft as it is equal to a Perfon that defires to fee quite round a Terrestrial Globe, fet in a proper Pofition; whether he walks himself round that Globe, while it ftands ftill; or whether the feveral parts of that Globe be turned round to him, while he ftands ftill: Which if it be granted; and the Vaftnefs of the Syftem about us be confider'd, with respect to the Smallness of our Earth; the immenfe fwiftnefs neceffary in one cafe, compar'd with the greater flownefs in the other; the prodigious diverfity of perplex'd Motions in the Sun, the Planets, the Comets, and the fix'd Stars to be provided for in the former Hypothefis, with the easy fimple Motion of one Globe about its own Axis to be allow'd in the latter; the difproportion, as to the probability of the

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one and the other Notion, will appear vaftly great and prodigious. Whether is it more fit and reasonable for 100 Auditors, in a Course of Geography, to have a Terrestrial Globe turned once round on its own Axis, in order to their diftinct and gradual view of the particular Countries thereon defcrib'd; or to have Carpenters fet to work to remove the Room, and the House it felf, and to carry it on Wheels in order to avoid that fingle Circumvolution? When once we are fatisfyed of the Juftness of fuch a procedure in the one Cafe,we may begin to think of allowing the like Juftnefs in the other; but not fooner.

(2.) There are no mechanical Laws of Motion known in the World, which can account for fuch a Diurnal Revolution of the Heavens; nay, it is directly contrary to all fuch known Laws whatsoever. 'Tis true, a Clock or Machine may have feveral diftin&t Motions within, and yet a Spectator may turn the whole round on its Axis at the fame time; becaufe all the Parts and Wheels are connected together, and take hold of each other, by material contract and infertion: So that he who removes one part, does of neceffity remove all the reft. But this is far from the real Cafe in the World about us; where the feveral Bodies are vaftly remote from, and unconnected with each other; and where therefore no fuch (imaginary) Revolution of any (fictitious) Primum Mobile, or material external Sphere can affect or move the feveral Bodies therein contain'd. When once we fee the Revolution of a large Wheel make other inward Wheels, which it does not touch, dance attendance thereto, and commence circular Revolu

tions round its Axis, we may begin to think of fuch a parallel Notion as to the prefent System, but not fooner.

(3.) There is no Example of fuch Periodical Revolutions, which carry different and feperate Bodies round the fame Axis, in the fame time, in the whole World about us. No Vortices or Whirlpools excited in Fluids do fo: None of the Primary Planets are carried fo about the Sun, nor Secondary ones about their Primaries. Nor indeed is the thing poffible in any mechanical Method whatfoever, agreeing to the prefent Syftem of things, that we know of. So that 'tis meerly an Hypothefis or Romance, unsupported by all good Evidence, and deriv'd entirely from the Prejudices and Notions of the Vulgar, before they are acquainted with the Principles neceflary to make them competent Judges in fuch Matters.

(4.) The frequent, if not conftant, Diurnal Revolutions of the reft of the Heavenly Bodies, renders it most highly rational, if not neceffary, to allow the like Revolution to our Earth. If we caft our Eyes abroad, and use Telescopes to affift them, we fhall find that Jupiter and Mars among the higher Planets; that Venus among the lower; that the Moon in our Neighbourhood; and that the Sun it felf in the Center of these Planetary Motions, have, for certain, fuch a diurnal Revolution about their own Axes. Nor is it any way certain, that either Saturn, or Mercury, the fecondary Planets, the Comets, or fixed Stars, i. e. that any of the Heavenly Bodies are deftitute of fuch a Motion. So that hence it is exceeding probable that our Earth may have the like Motion alfo.

(5.) The

(5.) The contrary Hypothefis introduces the utmoft Confufion into the apparent Heavenly Motions, while 'tis certain there is no manner of reafon for doing fo. For what strange Confufion is it to imagine, that while in Venus, in the Moon, in Mars, and in Jupiter, if not in all the other Planets and heavenly Bodies befides, there is fuch a diurnal Rotation, as feverally produces a regular fucceffion of Day and Night in them, according to the several natural Periods of thofe Revolutions; and while we cannot deny that the like diurnal Revolution of the Earth, would regularly produce a correfpondent regular Succeffion of Day and Night in 24 Hours with us, without the introduction of any farther Motions of the Heavens for this purpofe; what Confufion, I fay, is it after all, this, for us to introduce a ftrange, a violent, an unexampled, an unphilofophical Circumgyration of the whole vaft Universe about our poor Earth, every Day, to the diforder and perplexity of those other diurnal Appearances, and of the whole System? and all this without any just occafion in the World? If we were but for a while tranflated to Jupiter, which we know to have the quickeft diurnal Revolution of all the reft, and obferv'd how regular the rifing and fetting of the Sun,Moon, and Stars,appear'd therein from that diurnal Motion alone, I dare fay we fhould never after that so much as dream of any other than a diurnal Motion of our Earth, to account for the like rifing and fetting of the fame Sun, Moon, and Stars with us here upon Earth.

(6.) In Fact, our Earth certainly has fuch a diurnal Revolution about its own Axis, as we

are now fpeaking of: For though we do not ftand conveniently enough to fee the diurnal Revolution as to our own Earth, which we do as to the other Heavenly Bodies; yet are we capable of certainly knowing by one grand Effect of fuch a Motion, whether our Earth has that Motion or not? All Globes which have no diurnal Revolutions about their own Axes, muft, by the Equality of the weight of Bodies in all their Regions, be perfect Spheres; and all the Parts of their Surface muft, generally speaking, be at the fame diftance from the Center. But all Globes that have fuch a diurnal Rotation, See Sir I- (which will neceffarily be fwifteft at the Equafaac New- tor, and by confequence will caufe the Parts to ton's Prin- recede from the Axis of Motion, chiefly near cip.2d.Edit. the Equator) will be Oblate Sphæroids, or higher and p. 437, in the Equatoreal, and lower in the Polar Regi438. ons, as has been already obferv'd. Now to this

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certain do we appeal for the determination of this matter. For fince it appears from the leffer length of the Pendulum which vibrates Seconds near the Equator, than near the Pole; that the Surface of the Earth is about 31 Miles higher at the Equator, than at the Poles; and fince the regrefs of the Earth's Nodes, which we call the preceffion of the Equinox, with the Equilibration of the Waters near the Equator, and near the Poles, do both fully confirm the fame thing; all which are the neceffary Effects of the Earth's diurnal Rotation, and are accountable on no other Principles whatsoever; I conclude, that our Earth has fuch a diurnal Rotation; or, which is the fame thing, that the diurnal Revolution belongs to the Earth, and not to the Heavens.

N, B. I