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PROPOSITION VII.

The upper Parts of the Atmosphere are more subtile than those below; yet it may be, that those in the middle Region may be thicker and grosser than those' near tbe Earth.

FOR the lighter Parts go upwards and the more subtile Parts are the lighter, which shows the

Truth

in the Tube, gradually to subside; cular, and which deserves to but if again you shall by degrees be ranked among the noblest let in the Air, the Mercury in Inventions of the modern Phithe Tube will ascend, in pro- losophers. portion to the quantity of Air By the Experiments performintromitted, 'till at last it reach ed some time ago before the it's pristine Height of thirty Royal Society, for comparing Inches. This Apparatus, of the the Weight of Air with WaTube and Vessel, together with ter, and so with other Bodies; the contained Mercury, is, from by the first Experiment the proit's Use in measuring the Air, portion was found to be as I called a Barometer: and from to 840; by the next, as 1 to it's Author, Torricellius, any 8 5 2; and by the third as I to Experiment perform'd by means 860. And lately the Ingenithereof, is called Torricellian, ous Mr Hauksbee, by a very 'Tis manifest, that the Weight simple and accurately persormof the Mercury contained in the ed Experiment, found the RaTube, and the Weight of a Co- tie of Air and Water to be as lumn of Air, whose Altitude is 1 to 88;. All which Experithat of the whole Atmosphere, ments being made in the Sumand whose Basis is equal to the O- mer time, at which Season the risice of the Tube, if weighed se- Air is by the Heat expanded, parately, the one will be equal and consequently lighter; and to the other; so that when the the Barometer standing at about Weight of the Air is diminished, 29^ Inches higher; this might the Barometer is depressed, and perhaps be safely determined upviee versa. Hence by taking a on, that the Barometer ascendView of the Barometer, you ing to 30 Inches, and the Conmay, at any time, know the stitution of the Air at a Mepresent Gravity of the Airj dium, as to Cold and Heat, vi hich is a Problem of vast Mo- the Ratio of Air to Water would went both in Universal Physics, be as 1 to 800; and therefore and in Meteorology in parti- feeing, the Weight of Water

compared Truth of the first: Part of the Proposition: and the Cause of the second Part is, that those in the middle Region easily go together and become grosser, the hot Particles carried up with them having left them, and the Rays reflected from the Earth having but small force in the middle Region, that is so distant from the Earth.

WHENCEitis, that after Rain the middle Region is more clear; the grosser Part being fallen down (0).

PROPROPOSITION VIII.

compared with Mercury, is as i to 13 J, the Gravity of the Air compared to the Gravity of Mercury would be as I to 70800.

Juriris Appendix.

{q) If with the Hands we squeeze a blown Bladder, we feel the included Air make a strong Resistance, and by the Spring thereof, jumping back and disengaging itself, the Impressions, or Cavities, made by the Hands on the Surface of the Bl.idder, are immediately, on ceasing to press, expanded and smoothed; and this is called the Elastic Force of the Air. This Force, every Particle of Aircontinu.illy exercises, and affecting a larger Spice, contends against an equal Force of ambient Particles; whose Resistance being either fortuitously taken away or impaired, the Particle instantly expmds itself into the whole Extent, be it ever so large. Hence if slender glass Vials, or Bladders full of Air, and carefully stopp'd, be put into an Air-Pump, they are burst by the Force of the included Air.

Thus if a Bladder, only a little blown and flagging, be carried to the Top of a Mountain, or lofty Edifice, it immediately swells to such a Degree, that if the Mountain be of sufficient Height, it seems to be wholly stuffed with Air. For the Altitude of the Atmosphere not being the fame upon the Top of a Mountain, as upon the plain Surface of the Earth, the pressure of the ambient Air is not therefore so strong upon the Bladder placed there, and therefore the Air, included in it, springs into a larger Space. That the Air likewise upon the Top of a Mountain, is lighter than in Places of lower Situation, is evident from the Barometer, which being taken to the Top of a Mountain, the Mercury subsides; so that by means of it the Altitude, of Mountains might be very exactly calculated, were it once known in what proportion the Mercury falls; according to the different Height of the Place.

Vastly great, yea almost incredible is this elastic Force, by which,, according to the famous hious Mr Boyle*, the Air, without the Assistance of Heat, was dilated into a Space not only 60 or 150, but 8000, yea 10000, and at last $3769 times larger than that it possessed in it's natural State near the Surface of the Earth. And seeing the Air can he artificially compressed f to the sixtieth part of it's natural Space; it appears that the Place into which the Air may be artificially condensed, to the Place, into which it would dilate itself", if freed from all Pressure, is at least, as 1 to sixty times 13769; or more than 826000.

The Atmosphere, or Air, growing hot, takes up more Room than before, and the more the Heat leaves it, it contracts the more, and takes up less Room.

THIS is abundantly confirmed by that Instrument called a Thermometer, by which is measured surcd the Heat or Cold in the Air, for the colder the Air in the Glass, it takes up less Room, and

By a greatmany Experiments performed in England, France, and Italy, relating to the Contraction and Expansion of Air, it is found that the Spaces into which, by different Weights, it is condensed, are among themselves in a reciprocal Proportion to their Gravities; or, the greater the Pressure is on the Air, the less Space it possesses.

From which Theorem, together with the Proportion above

* Walla's Hjdroft. Prop. 13. •\Philos. Tran/aa. N°i8i.

determined betwixt the Weight of Air and Mercury, it is easy to fee the Grounds of the Controversies contained here and therein the Writings of the modern Philosophers, concerning the lesser density of the Air in the upper Regions, as also the Altitude of the whole Atmosphere.

First then, if we allow the the Air to have no Elasticity, but that thro' the whole Space 'twixt the Earth and the utmost bounds and extent of the Atmosphere it is every where of the fame Density; just as Water, which, howsoever deep, is every where from top to bottom equally dense; now since from what has been already said, it appears, that the Weight of a Column of Air, reaching to the top of the Atmosphere, is equal to the Weight of Mercury contained in a Barometer j and seeing also the Proportion of Weight betwixt equal quantities of Mercury and Air is found; it were easy to give a Definition of the Altitude of that Column of Air, or of the whole Atmosphere. For seeing a Column

the

lumn of Air one Inch high, it titude of the whole Atmo

to the like Column of Mercu- sphere divided into innumc

ry, as i to 10800, it appears rable equal Parts, seeing the

that these 10800 Columns, or Density of Air included in a

a Column of Air 900 Foot ny one of these Parts is in

"high, is equal in Weight to 1 proportion to it's quantity, and

Inch of the Mercury, and con- the Weight of the Atmosphere

sequently that all the 30 Inches is also as the quantity of the

of Mercury, contained in the whole incumbent Air; it ap

Barometer, require a Column of pears, that the quantity of the

Air 27000 Foot high. So that, whole incumbent Air is every

according to this Hypothesis, where, as the quantity of Air

the Altitude of the Atmosphere included in the lower Part,

would be only 27000 Foot, or which constitutes a Difference

a little more than 5 Miles. between every two nearest

But when, in the high Re- quantities of the whole incumgions, the Air, by it's elastic bent Air. It is a Theorem ia Force, resiles and expands it- Geometry; that such Magniself, according as the Weight tudes whose Differences are of the incumbent Atmosphere proportional to the Magnitudes is diminished, it must of neces- themselves, these Magnitude* fity be far more rarified and are in a continued geometrical subtile than the Air near the Proportion. Whence if, acSurface of the Earth: and con- cording to the Hypothesis, the sequently a much greater Alti- Altitude of the Air, by adding tude must be assigned to the the equal Parts, into which it is Atmosphere, than what was divided, increase in a continued found by the just now mention- arithmetical Proportion, it'* ed Computation. Density will be diminished, or.

For seeing, according to the which is the fame, the RareTheorem above laid down, the faction of the Air will be iaSpaces in which the Air is creased in a continued geomeincluded, are reciprocally pro- trical Proportion. Such as portional to the compressing know the way of following Gravities; but the density of e- such a Series, by taking a View very Body is in a reciprocal Ra- of one or more of the Rarefactitio to the Spaces, which that ons of the Air at different AltiBody possesses; the Density tudes, may, without any Troutherefore of the Air in any ble, determine it's Rarefaction Part of the Atmosphere will be in any Altitude, or the Altiproportional to the Weight of tude answering to any Rarefactithe whole incumbent Air. And on, and so also the Altitude of further, if we suppose the Al- the whole Atmosphere, if it may the more Room, the more Heat it acquires; as we lhall show in the following Proposition. The

natural

be known, or made the ex- the Air under different prestream Degree of Rarefaction, sures, had not been managed beyond which the Air cannot with sufficient Accuracy, they pass. Such as incline to know determined again to put the more on this Subject, may Matter upon Tryal, which Subconsult the famous Dr Gre- ject being diligently treated of gory's Astronomy, Lib. v. Prop, in the Royal Academy, and 3. as also the excellent Dr when there were made great Halleys Dissertation in Pbilo- Dilatations of Air, compared fophical Transactions N° 181 ■ to which, the Rarefactions found who have demonstrated the on the Tops of Mountains, fame in a different, and some- were woundrous small j yet they what more difficult way of found that all these exactly reasoning, which I have here followed the reciprocal Ratio borrowed from the Demon- of their incumbent Gravities, strations of a very learned So that it seems to be put Friend. beyond all doubt, that such is

But withal we must not the Nature of the Air, which conceal, that these things have comes nearest to the Earth's been rendered uncertain by the Surface, that the less pressure Observations of the famous it has upon it, the greater CaJ/ini * and his Assistants} Space it.dilates itself into: and who, in order to extend the seeing the upper Air, or such as Meridian Line of the Paris environs the Tops of Mountains, Observatory, after having with does not observe this Proporgreat exactness measured the tion, it follows, that it is of a Altitudes of several Mountains, different Nature from the Air and marked the Height of the that is next us, which notwithBarometer on the Top of each standing needs be no cause of of them, they sound that the wonder to us, if, according Rarefactions discovered by that to the most approved SentiMethod, noways agreed with ments of Philosophers, we althose we have lately laid down, low that there is in our Atbut that they were far greater mosphere, besides Vapours and than what ought to come out terrestrial Exhalations, a certain from the abovementioned Pro- Body of kin to itself, and enportion: whence becoming sus- dowed with such Affections, picious, that the Experiments as we have above assigned to they had formerly made for the Air j-and further, that these finding out the Rarefaction of Vapours and Exhalations, are

no ways capable of so great

* Hist de r Atad, Roy. 1703, Rarefaction, as is the Air; and

and 1705. that these arc mixed in far

greater

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