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 VAC

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VAC

hon-returning Curve 5 bccaufe in either of thofe Cafes, the Protrufion, and confequently the Refinance, Would be infinite. There remains, therefore, only the Motion in a revolving Curve practicable ; which mult either be a Revolution upon an Axis, or an annular Motion round a quiefcent Body 5 both which are, again, impoffible in an Elliptic Curve: And confequently, all Motion muft be in Circles geometri- cally true 5 and the revolving Bodies muft either be Spheres, Spheroids, Cylinders, or Portions of them, exactly geome- trical ; otherwife, their Revolutions in a Tlenum would be impoffible : But fuch Motions, or fuch figur'd Bodies, we do rot know in Nature. Therefore there is a Vacuum.

a. The Motions of the Tlanefs and Comets demonftrate a Vacuum : Thus Sir L Newtotz argues ; ' That there is no

of all fenfible Bodies, as the Sir and interstellar Tarts, and fo make a Plenum) ' feems probable j becaufe the Pla-
 * fuch fluid Medium as .dither, (to fill up the porous Tarts

« Motion thro' the Celeftial Spaces, both from and to all
 * nets and Comets proceed with fo regular and lafting a


 * Parts : For hence it appears, that thofe Celeftial Spaces


 * are void of all fenfible Refiftance, and confequently of


 * all fenfible Matter. For the refitting Force of fluid Me-

1 Medium, and partly from the Inactivity of Matter. Now
 * diums, arifes partly from the Attrition of the Parts of the


 * that Part of the Refiftance of any Medium, which arifes


 * from the Tenacity or Attrition of its Parts, may be leffen'd


 * by dividing the Matter into fmaller Parts, and by rendring


 * thofe Parts more fmooth and ilippery : But that Part ot

■ the Refiftance which arifes from the Inactivity of Matter, ' is always in proportion to the Denfity of the Matter ; nor


 * can be diminiffi'd by dividing the Matter, nor by any other


 * means, except by diminishing the Denfity thereof.

4 Water, or Quickfilver, they would refift almoft as much
 * Confequently, if the Culeftial Regions were as denfe as

■ as Water or Quickfilver; but if rhey were perfectly denfe,


 * without any interfoers'd Vacuity, tho the Matter were


 * ever fb fluid and fubtile, they would refift more than


 * Quicklilver does $ a perfectly folid Globe, in fuch a Me-


 * dium, would lofe above half its Motion, in moving three


 * Lengths of its Diameter ; and a Globe not perfectly folid,


 * fuch as the Bodies of rhe Planets and Comets are, would


 * be ftop'd ft ill fooner. Therefore, that the Motion of the


 * Planets and Comets may be regular and Iafting, it is ne-


 * ccflary the Celeftial Spaces be void of all Matter, except


 * perhaps feme few and much rarified Effluvia of the Pla-

Resistance, Medium, Planet, Comet, £j?c.
 * nets and Comets, and the paffing Rays of Light. See

3 . The fame great Author deduces a Vacuum from the Consideration of the Weights of Bodies 5 thus : * All Bo- 1 dies about the Earth gravitate towards the Earth ; and


 * the Weights of all Bodies equally diftant from the Earth's

« — If the jEther, therefore, or any other fubtile Matter,
 * Centre, are as the Quantities of Matter in thofe Bodies.


 * were altogether deftitute of Gravity, or did gravitate lefs


 * than in proportion to the Quantity of its Matter : Becaufe,


 * (as Arifiotle, 2)es Cartes, and others argue) it differs from


 * other Bodies only in the Form of the Matter ; the fame


 * Body might by the Change of its Form gradually be con-


 * verted into a Body of the fame Conftitution with thofe


 * which gravitate moft in proportion to the Quantity of


 * Matter : and on the other hand, the moft heavy Bodies


 * might gradually lofe their Gravity, by gradually chang-


 * ing their Form ; and therefore the Weights would depend


 * upon the Forms of Bodies, and might be chang'd with

4 . The 2)efcent of Bodies proves that all Space is not
 * 'em 5 which is contrary to all Experiment. See Weight.

equally full ; for the fame Author goes on, ' It all Spaces


 * were equally full, the Specifick Gravity of that Fluid with

c would not be lefs than the Specific Gravity of Quickfil-
 * which the Region of the Air would in that Cafe be fill'd,

' therefore, neither Gold, nor any other Body, could defcend
 * ver, or Gold, or any other the moft denfe Body ; and


 * therein. For Bodies do not defcend in a Fluid, un-


 * lefs that Fluid be fpecifically lighter than rhe Body. But


 * by the Air-Pump, we can exhauft a Veffel, till even a


 * Feather ftiall fall with a Velocity equal to that of Gold


 * in the open Air : The Medium, therefore, thro' which the


 * Feather falls, muft be much rarer than that thro* which


 * the Gold falls.' See Descent.

e may be diminifh'd by Rarefaction : and why may not it ' be diminifti'd in infinitum ? Add, that we conceive the
 * The Quantity of Matter, therefore, in a given Space,

1 and that they are only rarefiable by means of their Pores :
 * folid Particles of all Bodies to be of the fame Denfity ;

Pores, and Particle.
 * Whence a Vacuum evidently -follow.* SeeRAREFACTioN,

5°. ' That there is a Vacuum, is evident from the Vi- x brations of pendulums : For fince thofe Bodies, in Places


 * out of which the Air is exhaufted, meet with no Refif-


 * tance to retard their Motion, or fhorten their Vibrations 5


 * 'tis evident there is no fenfible Matter in thofe Spaces, or


 * in the occult Pores of thofe Bodies. See Pendulum.

For, as to what 2)es Cartes urges of his Materia Subtilise that its Tenuity prevents its Refiftance from being fenfible, and that a imall Body ftriking againft a greater, cannot in the leaft move, or refift the Motion of that other ; but is reflect- ed back again with all its Momentum : 'tis contrary to all Experience. For Sir Ifaac proves, that the Denfity of fluid Mediums, is proportionable to their Refiftances very nearly; and that they are exceedingly miftaken, who fuppofe the Refiftance of Projectiles to be infinitely diminifh'dj by di- viding the Parrs of the Fluid, even in infinitum. (Trincip- Lib. II. Prop. 38.) When, on the contrary, 'tis clear the Refiftance is but little diminifti'd by the Subdivision of the Parts ; (Ibid. Prop. 40.) and that the refilling Forces of all Fluids are nearly as their Denfities. For why ftiould not the fame quantity of Matter, whether divided into a great number of fubtile Parts, or into a few larger ones, have the fame refifting Force ? If then there were no Vacuum, ic would follow, that a Projectile moving in the Air, or even in a Space whence the Air is exhaufted, /hould move with as much difficulty as in Quicklilver ; which is contrary to Experience. Sec Projectile.

<S°. That there are Interfpers'd Vacuities, appears from Matter's being aBually divided into Parts, and from the Fi- gures of thofe Parts : For, on Suppofition of an ablolute Plenitude, we do not conceive how any Part of Matter could be actually divided from that next adjoining, any more than it is poffible to divide actually the Parts of abfolutc Space from one another : for by the actual Divifion of the Parts of a Continuum from one another, we conceive nothing elfe underftood, but the placing thofe Parts at diftances from one another which in the Continuum were at nodiftance from one another : But fuch Divifions between the Parts of Matter, muft imply Vacuities between. See Divisibility.

7 . As for the Figures of the Parts of Bodies, upon the Suppofirion of a Tlenum, they muft either be all Recti- linear, or all Concavo-convex 5 otherwife, they would not ade- quately fill Space; which we do not find to be true in Fact.

8°. The denying a Vacuum fuppofes what it is impoffible for any one to prove to be true, viz. That the material World hath no Limits. Sec Universe.

Since, then the Eflence of Matter does not confift in Ex- tenfion, but in Solidity, or Impenetrability, the Univerfe may be faid to confift of folid Bodies moving in a Vacuum : Nor need we at all fear, left the Phenomena of Nature, moft of which are plaufibly accounted for from a Plenitude, fhould become inexplicable when the ^Plenum is fet afide. The principal ones, fuch as the Tides ; the Sufpenfion of the Mercury in the Barometer 5 the Motion of the Hea- venly Bodies, of Light, &c. are more eafily and fatisfatto- rily accounted for from other Principles. See Tides, &c.

Vacuum, or Vacuum "Bdyleanum, is alfo ufed, fome- what abufively, to exprefs that approach to a real Vacuum^ which we arrive at by means of the Air-Pump. See Air- Tump.

Thus, any thing put in a Receiver fo exhaufted, is faid to be put in Vacuo : and thus, moft of the Experiments with the Air-Pump, are perform'd in Vacuo, or in Vacuo Boyleano.

Some of the principal Theenomena cbferv'd of Bodies m Vacuo, are ; That the heavieft and Jighteft Bodies, as a Guinea and a Feather, fall here with equal Velocity : — That Fruits, as Grapes, Cherries, Peaches, Apples, £=?£. kept for any time in Vacuo, retain their Nature, Frefhnefs, Colour, &c. and thofe wither'd in the open Air, recover their Plumpnefs in Vacuo:- — All Light and Fire becomes immediately extinct in Vacuo ; — The Collifion of Flint and Steel in Vacuo, produces no Sparks : — No Sound is heard, even from a Bell rung in Vacuo .— A fquare Viol, full of common Air, well clos'd, breaks in Vacuo ; a round one does not : — A Bladder half full of Air, will heave up 40 Pound weight in Vacuo : — Cats, and moft other Animals, readily expire in Vacuo.

By Experiments made in 1704, Mr. ZDerham found, that Animals which have two Ventricles, and no Foramen Ovale, as Birds, Dogs, Cats, Mice, ££?c. die in lefs than half a Minute ; counting from the firft Exfuction : A Mole died in one Minute ; a Bat liv'd feven or eight. Infects, as Wafps, Bees, Gra (hoppers, £gfc, feem'd dead in two Minutes ; but, being left in Vacuo 24 Hours, came to life again in the open Air : Snails continu'd 24 Hours in Vacuo, without ap- pearing much concerned.

Seeds planted in Vacuo don't grow : — Small Beer dies, and lofes all its Tafte in Vacuo .- — Lukewarm Water boils very vehemently in Vacuo : — Air, rufhing thro' Mercury in- to a Vacuum, throws the Mercury in a kind of Shower upon the Receiver, and produces a great Light in a dark Room. See Attrition, &c.

The Air-Pump can never produce a precifc Vacuum $ as is evident from its Structure, and the manner of its working : In effect, every Exfuction only takes out a part of the Air : fo that there will ftill be fome left, after any finite Number of Exfuctions. Add, that the Air-Pump has no longer any

effect,