PROPOSITION II.

The Atmosphere is all that Space about the Earth, in which the Vapours are; and it is uncertain if any thing else be contained in it but Exhalations.

IT is alfo taken for the Exhalations themselves that are about the Earth. It is no fmall Controverfy among the modern Philofophers, what that is which is about the Earth. Several famous Mathematicians are of Opinion there is nothing there but Exhalations; and fo the Atmosphere and Air is counted the fame: and above the Atmosphere is the æthereal Substance next it. Others think that there is a kind of Body befides these Exhalations, which is called Air, tho' they allow that Exhalations may turn to Air, and Air to thick Vapour and Clouds; and after this Air, all the Way to the Orbit of the Moon, they place another subtile Body, different from Ether, which they call Fire, indeed; but they confefs, improperly, as no way agreeing with our Fires; for it is hot, (tho' not burning) dry, and very fubtile, not caufing the Refractions of the Rays of the Sun and Stars, which they own to be in their Air. These things confidered, the two Opinions of the Philofophers differ rather in Words than in the Thing itself; for as to the Air, that is fo grofs as to caufe Refraction, and may be generated from Exhalations, that may be only a more refined Exhalation, tho' not from the Earth. As to the fublunary Fire, feeing they own it is improperly called fo, and is fo fubtile as to cause no Refraction, it seems to differ but little from the ethereal Matter; we may then fay the Atmosphere, or Air, is a Body about the Earth, into which the Rays falling, are refracted (laying afide the Question whence it comes); which Defi

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nition

nition agrees with the foregoing one, nor is it very likely a Body fo fubtile could be exhaled from the Earth, as to make no refraction or hinderance to the Rays of the Sun, that come thro' the Æther; and if there be fuch, we know how high they are or if they be out of the Atmofphere; which yet, if any would strongly maintain, believing the Particles of Fire that come from the Sun, on the Earth, do again travel back to it, they will not deny but the foregoing Definition. is proper. Therefore the Atmosphere and Air is nothing but a great many fmall Bodies interwoven together and adhering to the Earth; as the Down on a Quince or Peach.

PROPOSITION III.

There are fometimes more, fometimes fewer Exhalations fent up; especially in different Places.

zon.

THE Caufe is, 1. The different Elevation or Depreffion of the Sun above or below the Hori2. The different Age of the Moon, and it's Elevation above the Horizon. 3. The rifing and fetting of the other Stars, and their Situation above the Horizon. 4. The Difference in the Parts of the Earth; for Water and moift Places send out more Vapours than dry and earthy.

PROPOSITION IV.

The Exhalations that compofe the Atmosphere are of different Kinds, especially in different Countries, viz. watery, faline, fulphureous, earthy, and fpirituous.

THE Cause is, because there are fuch different Bodies in the Earth, and fome are most easily, and others with difficulty drawn up; fome may doubt

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doubt of the earthy Particles, because of their Weight; but yet this may be, 1. Because of the exceeding fmallness of the minute Particles of Dust, that have more Superficies in proportion to the quantity of Matter in them, and therefore are lighter. 2. Because of the mixture of fulphureous Particles, which carry them violently along with them.

AND that there are fulphureous Parts in the Air, appears from the fiery Meteors that are seen, as Lightning, Thunder, Jack with his Lanthorn, and the fulphureous Smell that is after Thunder and Lightning.

THERE can be no doubt of the watery Exhalations that are fpirituous and faline, they being very fmall and eafily drawn up, and the little Animals that are bred in the Air, in great Quantities do teftify the fame.

THE Ariftotelians divide Exhalations into two forts, Vapours, and Smoke. The Vapours are from the Water, and do eafily turn to Water again, and the Smoke from dry things; thus Sal Ammoniac turns all to Fume above the Fire; and hence it is that different Countries have different Air, and that it rains in one Place, and not in another.

PROPOSITION V.

The leaft and infenfible Particles of Air beat back or reflect all the Rays, as a Looking-Glafs doth; but fome of thofe that are perceivable and compounded tranfmit more Rays and reflect fewer; again, tranfmit fewer Rays and reflect more.

others

THEREFORE the Parts of the Air are divided into opake and pellucid; the former tranfmit fewer Rays, the latter more.

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BECAUSE

BECAUSE the leaft Particles, like Atoms both from the Earth and Water, are little folid Bodies without Pores, and therefore do reflect and difallow a Paffage to the Rays; for it is very probable, that Tranfparency, or the paffing of the Rays, requires Pores duly difpofed, and void of Matter.

BUT the Parts of the Atmosphere, or Air, that are compounded of the leaft Particles, if they have several Pores, duly difpofed, will be tranfparent and tranfmit many Rays; but if the Particles be joined very confusedly, and be without many Pores, they will not admit many Rays to pafs through.

HENCE it is, that the Sun difperfing a thick dark and cloudy Air, makes it more porous and transparent.

THAT the leaft Particles reflect the Rays, appears from this; if the Sun's Rays be admitted into a dark Room, in a clear Day, thro' a narrow Hole, you will clearly fee the Rays reflected in great Number.(from the Particles flying in the Air) to your Eye, as it were from a LookingGlafs; and as thefe Particles are ftill visible, we may conclude, in fome Degree, the fame of thofe that escape the Sight, and are leaft of all.

SOME would have the moift Exhalations to be tranfparent, and not the dry Fumes; but they are confuted by Experience and Reafon; 1. By Reafon; because the Fumes and dry Exhalations may become as fmall and porous as thofe that are moift; for they think that Transparency does not confift in Porofity, but that it is a peculiar Quality of the Medium: and 2. By Experience; because a clear Air hath more dry than moist Particles in it. This is understood from the new kind of WindGuns which are difcharged not by Powder and Fire, but by help of the Air, which is compreffed

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preffed and condensed, that it scarce takes up the fixtieth Part of the Room it had before, and yet there is no moiftnefs in the Gun; which must have been if the Particles of the clear Air had been from Water.

PROPOSITION VI.

Exhalations do not of themselves and of their own Nature afcend, but are forced up: or thus, the Air is not light, but heavy, confidered abfolutely.

ALL Things are faid to be heavy which would tend to the Center of the Earth if they were not hindered, and that the Air doth; for the Earth being dug, the Air goes down to the Room made there, and it's tending upwards is; 1. Because Heats rarifies and makes it take up a greater Room. 2. Because it is forced by other Vapours.

THUS in cold Countries, as Ñova Zembla, and with us, no Cloud afcends in the Night, but the Heat of the Sun coming on rarifies it, and makes one Part to prefs and force another: but if the leaft Particles of Air were not folded together, but at Liberty, they would move up and be light (P). PRO

(p) That Air is a ponderous Body, appears from a variety of Experiments, particularly one, from which it's Weight ufes likewife to be estimated.

Take a Glafs Tube, closed at one end, which fill with Quickfilver, then invert it with the open end, into a Veffel, alfo filled with Mercury, and the Mercury in the Tube will fo thwith fubfide, and after a few reciprocations, ftand at thirty Inches above the Surface of the Mercury, contained in the Veffel. The Reafon why the Quickfilver is fufpended at fuch a

Height is, because it is impoffible for it to defcend, unless at the fame Time the Mercury in the Veffel afcend; which, being on every Side preffed with the Weight of the ambient Air, cannot quit it's Place, unless the Weight of Air exceeded the Weight of Mercury in the Tube. And that this is the Cafe will appear from hence; put all the above-mentioned Apparatus into a large Receiver, out of which, by the Air-Pump, extract the Air; then, as the Air is extracted, you may perceive the Mercury, contained

in