Inftruments, and others in all probability farther and farther, with better and better Inftruments: And had we Inftruments of Power, equivalent to the Extent of Light, the luminous Bodies of the utmoft Parts of the Univerfe, would for the fame Reafon be vifible too.

Now as Light is of greateft Ufe to impower us to fee Objects at all, fo the Extenfion thereof is no lefs useful to enable us to fee Objects afar off. By which means we are afforded a Keh of thofe many glorious Works of the infinite Creator, vifible in the Heavens, and can improve them to fome of the nobleft Sciences, and moft excellent Ufes of our own Globe.

evident, that Light extends it felf to the utmost imaginable Parts, and by the help of Telescopes, we collect the Rays, and make them sensible to the Eye, which are emitted from fome of the almost inconceivably remote Objects, &c. Nor is it only the great Body of the Sun, for the vaft Bodies of the fixt Stars, that are thus able to difperfe Beir Light through the raft Expanfum of the Universe, but the smallest must do the thing, even the smallest Globule ftruck from a Steel by a Flint, &c.

Spark of a lucid Bodum BROT

HE laft thing fubfervient to our Globe, that I fhall take notice of, is Gravity (1), or that Tendency which Bodies have to the Centre of the Earth.

T

(1) That there is fuch a thing as Gravity is manifeft from its Effects here upon Earth; and that the Heavenly Bodies attract, or gravitate to one another, when placed at due diftances, is made highly probable by Sir Isaac Newton. This Attractive or Gravid

ting Power, I take to be copy the Creator and imprinted on 311

the Matter of the Universe by

That at the Creation.

What

In my Aftro-Theology, Book 6. Ch. 2. I have thewn of what abfolute Neceflity, and what a

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noble

What the Cause of it is, the Newtonian Philofophy doth not pretend to determine for want of Phænomena, upon which Foundation it is that that Philofophy is grounded, and not upon chimerical and uncertain Hypothefes: But whatever the Caufe is, that Cause penetrates even to the Centers of the Sun and Planets, without any dimi nution of its Virtue; and it acteth not according to the Superficies of Bodies (as Mechanical Caufes do) but in proportion to the Quantity of their Solid Matter; and lastly, it acbeth all round it at immenfe diftances, decreasing in duplicate proportion to thofe diftances, as Sir Isa ac Newton faith, Princip. pag. ult. What useful Deductions, and what a rational Philofophy have been drawn from hence, may be feen in the fame Book.

This Attraction, or Gravity, as its Force is in a certain proportion, so makes the Defcent of Bodies to be at a certain rate. And was it not for the Refiftance of the Medium, all Bodies would defcend to the Earth at the fame rate; the lightest Down at fwiftly as the heavieft Mineral: As is manifeft in the Air-Pump, in which the lighteft Feather, Duft, &c. and a piece of Lead drop down feemingly in the fame Time, from the Top to the Bottom of a tall exhaufted Receiver."

The rate of the Defcent of heavy Bodies, according to GalliLao, Mr. Huygens, and Dr. Halley (after them) is 16 Feet one Inch in one Second of Time; and in more Seconds, as the Squares of thofe Times. But in fome accurate Experiments made in St. Paul's Dome, June 9. 1710, at the Height of 220 Feet, the Descent was fcarcely 14 Feet in the first Second. The Experiments were made in the Prefence of fome very confiderable Members of the Royal Society by Mr. Hawksbee, their Operator, with glafs hollow Balls, fome empty, fome filled with Quick-filver, the Barometer at 297, the Thermometer 60 Degrees above Freezing. The Weight of the Balls, their Diameters, and Time of the Defcent is in this Table.

noble Contrivance this of Gravity is, for keeping the feveral Globes of the Univerfe from thattering -to pieces, as they evidently muft do in a little time by their swift Rotation round their own Axes (2). The Terraqueous Globe particularly, which circum

The reason why the heavy, full Balls fell in half the time of the hollow ones, was the Refiftence of the Air. Which Refiftence is very ingeniously and accurately affigned by Dr. Wallis, in Philos. Trans. N. 186. And the cause of the Refiftence of all Fluids, (as Sir Ifaac Newton, Opt. Q. 20.) is partly from the Priction of the parts of the Fluid, partly from the Inertia thereof. The Refiftence afpherical Body meets with from Friction, is as the right Angle under the Diameter, and the Velocity of the moving Body: And the Refiftence from the Vis-Inertie, is as the Square of that Product. For a farther Account of the Properties and Proportions, c. of Gravity in the Fall or Projection of Bodies, I fhall refer to the larger Accounts of Gallilaus, Torricellius, Huygens, Sir Ifaac Newton, &c. or to the thorter Accounts of Dr. Halley in Philof. Trans. abridged by Mr. Lowtherp, Vol. I. p. 561. or Dr. Clarke in his "Notes on Robault, Phyf. 2. c. 28. 9.13, 16. And for the Refiftence of Fluids, I refer to Dr. Wallis before-cited, and the Aft. Erudit. Lipf. May 1693 where there is a way to find the Force of Mediums upon Bodies of different Figures.

1

(2) That the heavenly Bodies move round their own Axes is, beyond all doubt, manifeft to our Eye, in fome of them, from the Spots vilible on them. The Spots on the Sun (eafily visible with an ordinary Glafs) do manifeft him to revolve round his own Axis in about 254 Days. The Spots on and prove thofe two Planets to revolve also from East to Weft, as Dr. Hook difcover a in 1664, and 1665. And ₺ alfo (although near the strong Rays of the Sun) hath, from fome Spots, been discovered by Mr. Caffin, in 1666, and 1667, to have a Manifeft Rotation. V. Lowth. Abridg. Vol. 1. p. 382, and 423, 425. And fuch Uniformity hath the Creator obferv'd in the Works of Nature, that what is observable in one, is generally to be found in all others of the fame kind. So that fince 'tis manifest the Sun, and three of his Planets whirl round, it is very reasonable to conclude all the reft do fo too, yea, every Globe of the Universe.

volves at the rate of above 1000 Miles an Hour (3), would by the centrifugal force of that Motion, be foon diffipated, and fpirtled into the circumambient Space, was it not kept together by this noble Contrivance of the Creator, this natural inherent Power, namely, the Power of Attraction, or Gravity.

And as by this Power our Globe is defended against Diffipation, fo all its Parts are kept in their proper Place and Order. All material Things do naturally gravitate thereto, and unite themselves therewith, and fo preserve its Bulk intire (4). And the fleeting Waters, the moft unruly of all its Parts, do by this means keep their conftant æquipoife in the Globe (5), and remain in that Place which, the Pfalmift faith, God had founded for them; a bound he

(3) The Earth's Circumference being 25031 Miles, (according to Book II. Chap. 2. Note 1.) if we divide that into 24 Hours, we fhall find the Motion of the Earth to be nearly 1043 Miles in an Hour. Which, by the by, is a far more reasonable and lefs rapid Rate, than that of the Sun would be, if we fuppofe the Earth to stand still, and the Sun to move round the Earth. For according to the Proportions in Note 5, of the preceding Chapter, the Circumference of the Magnus Orbis is 540686225 English Miles, which divided by 24 Hours, gives 22521364 Miles in an Hour. But what is this to the Rapidity of the fixt Stars, if we fuppofe them, not the Earth, to move? Which is a good Argument for the Earth's · Motion.

(4) Nihil majus, quam quod ita ftabilis eft Mundus, atque ita cohæret ad permanendum, ut nihil ne excogitari quidem poffit aptius. Omnes enim partes ejus undique medium locum capeffentes nituntur equaliter: maxime autem corpora inter fe juncta permanent, cum, quodam quafi vinculo circumdata colligantur: quod facit ea natura, que per omnem mundum omnia Mente, & Ratione conficiens, funditur, & ad medium rapit, & convertit extrema, Cic. de Nat Deor. 1. 2. c. 45.

(5) Eadem ratione Mare, cum fupra terram fit, medium tamen terra locum expetens, conglobatur undique aqualitèr, neque redundat unquam, neque effunditur. Id. paulo poft.

bad

bad fet, which they might not pass; that they turn not again to cover the Earth, Pfal. 104. 8, 9. So, that even in a natural Way, by virtue of this excellent Contrivance of the Creator, the Obfervations of the Pfalmift is perpetually fulfilled, Pfal. 89. 9. Thou rulest the raging of the Sea; when the Waves thereof arife, thou ftilleft them.

To thefe, and an hundred other Ufes of Gravity that I might have named, I fhall only juft mention another thing owing to it, and that is Levity (6), that whereby, what we call light Bodies fwim, a thing no lefs ufeful to the World than its oppofite, Gravity, is in many Refpects, to divers Tribes of Animals, but particularly ferviceable to the raifing up of Vapours 7), and to their conveyance about the World.

(6) That there is no fuch thing as pofitive Levity, but that Levity, is only a leffer Gravity, is abundantly manifested by the acute Seig. Alph. Borelli de Mot. à Grav. pend. cap. 4. See alfo the Annotations of the learned and ingenious Dr. Clark on Rohaulti Phyf. p. 1. c. 16. Not 3. Alfo the Exper. of the Acad. del Cimento, p. 118. &c. Dr. Wallis's Difc. of Gravity and Gravitation before the Royal Society, Nov. 12. 1674. p. 28, &c.

(7) I have before in Note 1. Chap. 3. fhewn what Vapours are, and how they are rais'd. That which I fhall here note, is their Quantity. Concerning which the before commended Dr. Halley hath given us fome curious Experiments in our Phil Tranfact, which may be met with together in Mr. Lothorps Abridg. Vol. II. p. 108. and 126. Mr. Sedileau alfo at Paris obferved it for near three Years, By all their Obfervations it appears, that in the Winter Months the Evaporations are leaft, and greateft in Summer, and most of all in windy Weather. And by Monfieur Sedileau's Obfervations it ap pears that what is raised in Vapours, exceeds that which falleth in Rain. In the Seven laft Months of the Year 1688, the Evapora tions amounted to 22 Inches 5 Lines; but the Rain only to 11 Inches 6 Lines: In 1689, the Evaporations were 32 Inches 10! Lines; but the Rain 18 Inches 1 Line: In 1690, the Evaporations 30 Inches 11 Lines; the Rain 21 Inches of a Line. Vid. Mem. de Math. Phyf. Ann. 1692. p. 25. D 2

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