Page:Cyclopaedia, Chambers - Volume 1.djvu/95

 A I R

C 50)

A I R

Thus much for Air confidcr'd in it felt*. But fuch Air,

we have obferv'd, no where exifts in its Purity.— That wherewith we are concern'd, and whofe Properties and Ef- fects are chiefly confider'd, is acknowlcdg'd by Mr. Boyle to be the moft heterogeneous Body in the Univerfe : Boer- haave even mews it to be an univerfal Chaos, or Colluvies of all the Kinds of created Bodies.— Whatever Fire can volatilize is found in the Air ; but there is no Body that can withttand the Force of Fire. See Fire, Volatility, Burning-Glass, &c.

Hence, for inftance, the whole Foflil Kingdom mutt ne- ceffarily be found therein : For all of that Tribe, as Salts, Sulphurs, Stones, Metals, &c. are convertible into Fume, and thus capable of being render'd part of the Air.— Gold it felf, the molt fix'd of all natural Bodies, is found to ad- here clofe to the Sulphur in Mines 5 and thus to be raifed along with it. See Gold, $£c.

a, All the Parts of the Animal Kingdom mutt alfo be in the Air : For, betide the copious Effluvia continually emitted from their Bodies, by the vital Heat, in the ordi- nary Courfe of Perfpiration $ by means whereof an Animal, in the Courfe of its Duration, impregnates the Air with many times the Quantity of Its own Body, (See Perspira- tion, Effluvia, iyc.) Befide this, we find that any Ani- mal when dead, being expofed to the Air, is in a little time carried wholly off, Bones and all. So that the Whoie of what before was an Animal, e.g. a Man, an Ox, or the like, is now in the Air,

By the way, it may be noted what huge Swarms of the groffer excrememitious Matters of Animals mutt Iwim in the Air: At Madrid, we are afiured, they have no Neceffary Houfes 5 and thar they always make a Jakes of their Streets overnight : yet does the Air imbibe the tilth as faff as 'tis laid 5 intbmuch, that there is no increafe of any fetid fmeli.

3, As to Vegetables, nothing of that Clafs can be fuppo- fed wanting ; fince we know that all Vegetables by Putri- fa&ion become volatile 5 even the earthy or vafcular Part, in time follows the reft. See Vegetable, Plant, £=fc. .

Of all the Effluvia floating in this grand Ocean the At- mofphere $ one of the principal, are the Saline. Thefe, Au- thors commonly conceive, as chiefly of the nitrous Kind ; but there is no doubt but that there are of all the forts, Vi- triolick, Aluminous, Sea Salt, £#c. See Salt, Nitre, %$e.

Mr. Boyle even obferves, that there may be many com- pounded Kinds of Salts in the Air, which we have not on Earth; arifing from different faline Spirits, fortuitouily meet ing and mixing together. — Thus, the glafs Windows of antient Buildings are fometimes obferv'd to be corroded, as if they had been Worm-eaten 5 tho none of the Salts abovemen- tion'd have the Faculty of corroding Glafs.

The Sulphurs, too, mutt make a coniiderable Article in the Air ; on account of thofe many Volcanoes, Grottos, Ca- verns, and other Spiracles chiefly affording that Mineral, difperfed thro' the Globe. See Sulphur, Volcano, £*?c.

And the Affociations, Separations, Attritions, Diflolutions, and other Operations of one fort of Matter upon another, may be confider'd as a Source, of numerous other neutral or anonymous Bodies, unknown to us.

Air, in this general Senfe, is one of the moft coniiderable and univerfal Agents in all Nature j being concern'd in the Production of moft of the Phenomena relating to our World. — Its Properties and Effects, including a great Part of the Refearches and Difcoveries of the modern Philofophers, have fome of 'em been reduced to precife Laws and De- monftrations ; in which form they make a Branch of Mathe- rnaticks, called Pneumaticks, or Aerometry. See Mathe- maticks, Pneumaticks, and Aerometry.

Mechanical 'Properties and Ejfebls of Air.

F, Fluidity. That the Air is a Fluid, is evident from

the eafy Paffage it affords to Bodies thro' it 5 as in the Propagation of Sounds, Smells, and other Effluvia : For this argues it a Body whofe Parts give way to any Force im- prefs'd, and in yielding, are eafily moved among themfelves ; which is the Definition of a Fluid. See Fluid. — See alfo Sound, &c.

They who, with the Cartefians, make Fluidity confitt in a perpetual inteftine Motion of the Parts, find Air alfo an- Jwers to that Character : Thus, in a darkned Room, where the Species of extetnal Objects are brought in by a fingle Ray: they appear in a continual Fluctuation 5 and thus even the more accurate Weather-Glaffes are obferv'd never to re- main a moment at reft. See Weather-G/^/J.

The Caufe of this Fluidity of Air, is attributed by fome late Philofophers to the Fire intermixed therewith ; with- out which, they imagine, the Atmofphere would harden into a folid, impenetrable M^tfs. — And hence, the greater the Degree of Fire therein, the more fluid, moveable and per- vious the Air : And thus, as the degree of Fire is continu- ally varying 5 according to the Circumftances and Pofition of

the heavenly Bodies ; the Air is kept in a continual Reci- procation. See Fire.

Hence, in good meafure, it is, that on the Tops of the higher Mountains $ the Senfes of Smelling, Hearing, &c. are found very feeble. See Mountain.

II, Weighty or Gravity.- That the Air is heavy, fol- lows from its being a Body ; Weight being an cfiential Pro- perty of Matter. See Weight, and Gravity.

But we have infinite Arguments of the fame from Senfe, and Experiment : Thus, the hand, applied on the Orifice of a Veffcl empty of Air, foon feels the Load of the incum- bent Atmofphere. — Thus, glafs Veffels, exhautted of their Air, are eafily crufh'd to pieces by the Weight of the Air without. So, two fmall hollow Segments of a Sphere, ex- actly fitting each other, being emptied of Air, are piefs'd together with a Force equal to 100 Pound, by the Pondus of the ambient Air.

Further, a Tube clofe at one end, being filled with Mer- cury, and the other End immerged in a Bafon of the fame Fluid 5 and thus erected : The Mercury in the Tube will be fufpended to the Height of about 50 Inches above the Surface of that in the Bafon. The Reafon of which Sufpenfion, is, that the Mercury in the Tube cannot fall lower, without railing that in the Bafon 5 which being prefs'd down with the Weight of the incumbent Atmo- fphere, cannot give way, unlefs the Weight of the Mercury in the Tube, exceeds thar of the Air out of it. — That this is the Cafe, is evident hence 5 that if the whole Apparatus be included in an Air-Pump ; in proportion as the Air is ex- hautted from the fame, the Mercury tails: and gradually let- ting in rh<: Air again, the Mercury reafcends to its former height.— This makes what we call the Torricellian Experi- ment., See Torricellian.

To fay no more, we can actually weigh Air : For a Vef- fel, full even of common Air, by a very nice Balance, is found to weigh more than when the Air is exhautted ; and the EffecT: is proportionably more fenfible, if the fame Vef- fel be weigh'd full of condenfed Air, and void of Air. See Weighing, and Hyi>rostatical Balance.

The Weight of Air is continually varying, according to the different degree of Heat, and Cold. — Ricciolus eftimates its weight to that of Water, to be as 1 to 1000 ; Mer- fenmts as 1 to 1300, or 1 to 1355 5 Galileo only makes it as 1 to 400. — Mr. Beyle, by a- more accurate Experiment, found it about London, as 1 to $38 5 and thinks, all things confi- der'd, the Proportion of 1 to 1000 may be taken as a Medium; for there is no fixing any precifeRatio, fincenot only the Air y but the Water it feif, is continually varying. Add, that Ex- periments made in different Places neceffarily vary, in re- gard of the different Heights of the Places, and the diffe- rent Confittences of Air arifing therefrom. Boyle, e Phyf Mecban. Exper.

It mutt be added, however, that by Experiments made fince before the Royal Society ; the Proportion of Air to Water was, firft, found as 1 to 840 5 then, as 1 to 852 ;

and a third time, as 1 to 8tfo. "Phil. Tranf. N° 181.

And lattly, by a very fimple and accurate Experiment of the late Mr. Hawkshee ; the Proportion was fettled as r to 88 j.

"Pbyf. Mecban. Exper. But thefe Experiments being all

made in the Summer Months, when the Barometer was 29 Inches •*- high ; Dr. Jurin thinks, that at a Medium be- tween Heat and Cold, when the Barometer is 30 Inches high ; the Proportion between the two Fluids, may be taken as 1 to 800.

Air, then, being heavy and fluid ; the Laws of its Gra- vitation, or Preffure, may be inferr'd to be the fame as in other Fluids ; confequently, its Preffure mutt be as its per- pendicular Altitude. See Fluid.

This is alfo confirmed by Experiment. — For, removing the Torricellian Tube to a more elevated Place, where the in- cumbent Column of Air is fhorter 5 a proportionably fhorter Column of Mercury is fuffained ; it being found to defcend at the Rate of one fourth of an Inch, for every 100 Foot of Afcent. See Levelling.

On this "Principle depends the StruBure and Office of the Barometer. See Barometer.

From hence, alfo, it follows, that the Air, like all other Fluids, mutt prefs equally every way.— Which is confirm'd by what we obferve of foft Bodies futtaining this Preffure without any Change of Figure 5 and brittle Bodies, without their breaking $ tho the Preffure upon 'em be equal to that of a Column of Mercury 30 Inches high, or a Column of Wa- terof 32. Foot. — 'Tis obvious, that no other Caufe can pre- ferve fuch Bodies unchanged, but the equable. Preffure on all Sides, which refifts as much as it is refitted. And hence, up- on removing or diminiffung the Preffure on one fide only; the Effecl of the Preffure is foon perceiv'd on the other.

For the Quantity and EffeB of this "Preffure of the At- mofphere on the human Body. See Atmosphere.

From this Gravity of the Air, confidcr'd with its Fluidi- ty, feveral of its Ufes and Effects are deducible.— And, i°, by means hereof, it clofely invefts the Earth, with all the a Bodies