A I R 



A T R 



fame with tlieir other, or that fine, fluid, aftive mSttcv, 

 dill'ulV'd through the whole expanfe of the colcllial regions ; 

 which coincides with Sir I. Newton's fiibule medium, or 

 fj)irit. In this view it is iuppofed to bi a bodv fui generis, 

 ingenerable, incorruptible, immutable, prcfeut in all places, 

 ami in all bodies. 



Others, confidcring only its property of elafticity, which 

 they account its effential and conftituent charadlcr, fuppufe 

 it to be mechanically producible ; and to be no other than 

 the matter of other bodies, fo modified and altered, as to 

 become permanently clallic. Sir Ifaac Newton obfenes, 

 that the particles of denle, compatt, and fixed fubllances, 

 cohering by a ilrong attradive force, are not feparable 

 without a vehement heat, or perhaps not without fermen- 

 tation ; and fucli bodies being at length rarefied by fuch 

 hjat or fermentation, become true psrmancitt air ; and dil'- 

 tinguilliable from vapour, which is only tippiirnit, or truii- 

 Jlcnt Liir, as is evident from the experiment with the reoli- 

 pile. Optics, Qu. 31, p. 371, 372. cd. 3. See Air, 

 atmofpherical. 



Air, I'lihrar or heterojeueous, is a conlition of coi-puf- 

 clcs of various kinds, conllituting togetlier one fluid miifr., 

 in which we Iwe and move, and which we are continually 

 rijceiving and expelling by refpiration. The whole afrcni- 

 blage of this makes what we call the atmofphere ; where 

 this air, or atmofphere, terminates, there alinr is fuppofed 

 to commence ; wliich is dilHnguifh.'d from air bv its not 

 making any fenfible refraction of the rays of light, as air 

 does. 



Air, in this popular and extenfive meaning of the term, 

 is acknowledged by Mr. Boyle to be the moil heterogeneous 

 body in the univerfe. Boerhaave fliews it to be an univerfal 

 chaos, or colluvies, of all kinds of created bodies. Bcfidcs 

 the matter of light or fire, which continually flows into it 

 from tht heavenly bodies, and probably the magnetic effluvia 

 of the earth ; whatever fire can volatilize is found in the air. 



Hence, for inftance, I. The whole foffiJe kingdom muil 

 neceffarily be found in it ; for all of that tribe, as falts, ful- 

 phurs, ftones, metals, &c. are convertible into fume, and 

 thus capable of being rendered part of the air. Gold itfelf, 

 the moll fixed of all natural bodies, is found to adhere dole 

 to the fulphur in mines ; and thus to be railed along with it. 

 Mr. Boyle obferves, that befide the faline effluvia of the 

 common fort, fuch as the nitrous, vitriolic, marine, &ic, 

 there may be many compounded kinds of falts in the air, 

 which we have not on earth, arifiug from different faline 

 fpirits, fortuitoudy meeting and mixing together. Thus, 

 the glals windows of ancient buildings are iomelimes oh- 

 fcrved to be corroded, as if they had bee:i worm-eaten ; 

 though none of the fimple falts above-mentioned have the 

 faculty of corroding glafs. 



Sulphurs too muil make a confiderable ingredient of tlie 

 air, on account of thofe many volcanos, grottos, caverns, 

 and other fpiraclcs rfiiefly affording that mineral, difperfed 

 through the globe. 



2. All the parts of the animal kingdom mufl alfo be in 

 the air; for befides the copious effluvia continually emitted 

 from their bodies,- by the vital heat, in the ordinary procefs 

 of perfpiration ; by means of which an animal, in the courfe 

 of its duration, impregnates the air with many times the 

 quantity of its own body ; we find that any animal when 

 dead, being expofed to the air, is in a certain time wholly 

 incorporated with it. 



3. As to vegetables, none of tliat clafs can be fuppofed 

 wanting ; fince we know that all vegetables, by putrefaction, 

 become volatile. 



The alTociation?, fcparations, attritions, difTolutions, and 

 other operations of o.ie fort of matter upon another, may 

 likcwife be confidertd as fources of numerous other neutral, 

 or anonymous bodies, unknown to us. 



4. Water is alfo dillufed through the air in great abun- 

 dance. Many familiar inllaiices might be alledged to thi* 

 purpofe. A bottle of wine, when taken out ot the cclLir 

 in the dried and hottcllday of fummer, will foon be covered 

 with a denfe vapour, wiiich is water dcpolited by the uir. 

 The fame appearance is obferved on the outfide of any me- 

 tallic velfel, wiiieh, in warm weather, contains water cooled 

 by ice or the fylution of fait, or even Ipring water, which is 

 fome degrees colder than the aii'. For othei- fadls of fimilar 

 kind, fee Water. 



Air, in this general fenfe, is one of the moll confiderable 

 and univerfal agents in all nature ; being concerned in the 

 prefervation of life, and the production of moll of the phe- 

 nomena relating to our world. Its properties and cfiecls, 

 including a great part of the refearches and difcoveries of the 

 modern philofopliers, have in a confiderable degree been re- 

 duced to precife laws and demonilrations, in which form they 

 make a very exteiilive and important branch of the mixed 

 mathematics, called hneumatics. 



Air, mi'i-h.inhal propert'ns ait J effeSs of. The mod 

 coniiderablc of thefe are its Jlu'uUty, tueigLt, and e!af- 

 tk'ily. 



I. Fht'hlily. That the air is a fluid, is evident from the 

 eafy paflage it affords to bodies through it ; as in the pro- 

 pagation Oi fraclls, and other effluvia, and the eafy con- 

 veyance it affords to founds : for thefe and fimilar effects 

 prove it to be a body, whofe parts give way to any forco 

 impreffed, and, in yielding, are eafily moved among them- 

 felves ; which is the definition of a fluid. Befides, it is cer- 

 tain, that no condenfation by jireffure, nor any degree of 

 cold that has ever yet been produced, natural or artificial, 

 have been fufiicient to deprive it of its fluidity. It is true, 

 indeed, that real pentianent air may be extracled from folid 

 bodies, and may be alfo ablorbed by them ; and in this fl.att: 

 it mufl be very much condenfed : but under what form it 

 exills in thofe bodies, or how its particles are combined 

 togetlier, the refearches of philofopliy and chemillr)- have 

 not yet been able to explore. 



They who, with the Cartefians, make fluidity to confifl 

 in a perpetual intefline motion of the parts, find that air 

 anfwers alfo to that charatler : thus, in a darkened room, 

 where the fpecies of external objeils are brought in by a 

 finglc ray, they appear in a continual fluctuation ; and thus 

 even the more accurate thermometers are obferved never to 

 remain a moment at refl:. 



The caufe of this fluidity of air is attributed by fomc 

 later philofophers to the fire intermixed with it ; without 

 which, they imagine, the atmofphere would harden into 

 a folid impenetrable mafs. And hence, the greater the 

 degree of fire, the more fluid, moveable, and pervious is the 

 air : and thus, as the degree of fire is continually vaiying, 

 according to the circumllances and pofition of the heavenly- 

 bodies, t!ie air is kept in a continual reciprocation. See 

 Buffon's Hill. Nat. Supp. vol. i. Hence, in a great mea» 

 fure, it is faid, that on the tops of the higher mountains, 

 the fenles of fmelling, hearing, &c. are found very feeble. 

 The increafcd rarity of the air at a confiderable height may 

 account for this effect ; but the above hypothefis is con- 

 tradicled by the more fenfible experience of cold : the air, 

 near the furface of the earth, deriving greater heat from the 

 reflecled than from the diredl rays of the fun. See Moun- 

 r.iiNS. 



3 M 2 n. Weight 



