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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.

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IT is also taken for the Exhalations themselves that are about the Earth. It is no small Controversy among the modern Philosophers, what that is which is about the Earth. Several famous Mathematicians are of Opinion there is nothing there but Exhalations; and so the Atmosphere and Air is counted the same: and above the Atmosphere is the æthereal Substance next it. Others think that there is a kind of Body besides 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 Æther, which they call Fire, indeed; but they confess, improperly, as no way agreeing with our Fires; for it is hot, (tho'not burning) dry, and very subtile, not causing the Refractions of the Rays of the Sun and Stars, which they own to be in their Air. These things considered, the two Opinions of the Philosophers differ rather in Words than in the Thing itself; for as to the Air, that is so gross as to cause Refraction, and may be generated from Exhalations, that may be only a more refined Exhalation, tho'not from the Earth. As to the sublunary Fire, seeing they own it is improperly called so, and is so subtile as to cause no Refraction, it seems to differ but little from the æthereal Matter ; we may then say the Atmosphere, or Air, is a Body about the Earth, into which the Rays falling, are refracted (laying aside the Question whence it comes) ; which Definition agrees with the foregoing one, nor is it very likely a Body so subtile 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 such, we know how high they are or if they be out of the Atmosphere ; 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 small Bodies interwoven together and adhering to the Earth ; as the Down on a Quince or Peach.

PROPOSITION III.

There are sometimes more, sometimes fewer Exhala.

tions sent up; especially in different Places.

THE Cause is, 1. The different Elevation or Depression of the Sun above or below the Horizon. 2. The different Age of the Moon, and it's Elevation above the Horizon. 3. The rising and setting of the other Stars, and their Situation above the Horizon. 4. The Difference in the Parts of the Earth; for Water and moist Places send out more Vapours than dry and earthy.

PROPOSITION IV.

The Exhalations that compose the Atmosphere are of

different kinds, especially in different countries, viz. watery, saline, sulphureous, earthy, and spirituous.

THE Cause is, because there are such different Bodies in the Earth, and some are most easily, and others with difficulty drawn up ; some may Ee 3

doubt

doubt of the earthy Particles, because of their Weight; but yet this may be, I. Because of the exceeding smallness 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 sulphureous Particles, which carry them violently along with them. • AND that there are sulphureous Parts in the Air, appears from the fiery Meteors that are seen, as Lighining, 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 spirituous and saline, they being very small and easily drawn up, and the little Animals that are bred in the Air, in great Quantities do testify the same,

THE Aristotelians divide Exhalations into two forts, Vapours, and Smoke. The Vapours are from the Water, and do easily 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."

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HE Aristotelian, Smoke. The Vapo water

PROPOSITION V. The least and insensible Particles of Air beat back or

refleEt all the Rays, as a Looking-Glass doth; but . Some of those that are perceivable and compounded

transmit more Rays and reflext fewer ; Others · again, transmit fewer Rays and refleEt more.

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

BECAUSE

BECAUSE the least Particles, like Atoms both from the Earth and Water, are little solid Bodies without Pores, and therefore do reflect and disallow a Passage to the Rays; for it is very probable, that Transparency, or the pasling of the Rays, requires Pores duly disposed, and void of Matter.

BUT the Parts of the Atmosphere, or Air, that are compounded of the least Particles, if they have several Pores, duly disposed, will be trantparent and transmit many Rays ; but if the Particles be joined very confusedly, and be without many Pores, they will not admit many Rays to pais through.

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

THAT the least 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 see the Rays reflected in great Number-(from the Particles flying in the Air) to your Eye, as it were from a LookingGlass; and as these Particles are still visible, we may conclude, in some Degree, the same of those that escape the Sight, and are least of all.

SOME would have the moist Exhalations to be transparent, and not the dry Fumes; but they are confuted by Experience and Reason; 1. By Reason; because the Fumes and dry Exhalations may become as small and porous as those that are moist ; for they think that Transparency does not consist in Porosity, 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 discharged niot by Powder and Fire, but by help of the Air, which is comEe 4

pressed

pressed and condensed, that it scarce takes up the sixtieth Part of the Room it had before, and yet there is no moistness 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 ascend, but are forced up: or thus, the

Air is not ligbt, but beavy, considered absolutely.

ALL Things are said 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.

THU S in cold Countries, as Nova Zembla, and with us, no Cloud ascends in the Night, but the Heat of the Sun coming on rarifies it, and makes one Part to press and force another : but if the least Particles of Air were not folded together, but at Liberty, they would move up and be light (P).

PROc) That Air is a ponderous Height is, because it is imporBody, appears from a variety of sible for it to descend, unless at Experiments, particularly one, the same Time the Mercury in from which it's Weight uses the Vesel ascend; which, belikewise to be estimated. ing on every Side pressed with

Take a Glass Tube, closed at the Weight of the ambient Air, one end, which fill with Quick- cannot quit it's Place, unless the silver, then invert it with the o- Weight of Air exceeded the pen end, into a Vessel, also filled Weight of Mercury in the with Mercury, and the Mercury Tube. And that this is the Case in the Tube wil.fo thwith sub- will appear from hence; put fide, and after a few recipro- all the above-inentioned Appacations, Itand at thirty Inches ratus into a large Receiver, out above the Surface of the Mer- of which, by the Air. Pump, cury, contained in the Vessel. extract the Air; then, as the The Reason why the Quicksil. Air iş extracted, you may perver is suspended at such a ceive the Mercury, contained

in

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