OCR Text |
Show A Al Mr. Boyle found that a Lamb's Bladder containing about two Thirds of a Pint, and blown up, and well dry’d, loft about a Grain and one Eighth when it was prick’d, and the ah: Air let out. Mr. Gravefende found, that the Airin a Glafs Ball of about 283 Inches Capacity, weigh’d an hundred Grains; and according t Foot of Air isin to Burcber de Volder, a Weight one Ounce and twenty-feven Grains Mr. Boyle has computed, that the Weight of any Quantity of dir, near the Surface of the Earth, isto Water as 1 to 1000; and Dr. by, 800; and Mr. Ha to 885, and the Gravity of the fame Quantity of 4ir to the fame Quantity of Mercury, as ‘ I to 10800. Asto the Ufe and Effects of this Preffure of the 4ir, the Weight of the whole incumbent bles it to fuftain the Mercury Airis fuchas in the Zo *'\oneegeoan im Tube to the Height of 28 Inches, and Water to that of 32 Feet: But the Weight or Gravity of the dir is conrent ing, according to the tinually Degree of Heat and Cold ; and Experiments made in different Places neceflarily vary in regard of the different Heights of the Places, and the Differences of 4ir arifing therefrom : Andfo the Mercury in a Barometeris found to defcend a fourth Part of an Inch for every 100 Foot of Afcent Air therefore may be confider’d as an uni- a tatenetrai Susueaeiananna verfal Opercu/um or Cover, which by its Weight keeps all terreftrial Bodies down, and Al the ambient Particles of Air: as the Re fiftance happens byany meansto be weaken’d, it immediately diffufes itfelf into a vaft Ey. tent. This Power or Property of the Air does not feem to have any Limits afligned it, Mr, Boyle, by feveral Experiments, dilatedit firft into 9 times its Space, then into 31, then into 60, then into 150; afterwards it was brought to dilate into 8000 times its Space, then into 10000, and at laft into 13679 times its Space; andall by its own expanfive Force, without any HelpofFire. From thefe Experiments, and many others, it appears, that the we breathe near the Surface of the Earth is comprets’d byits own Weight into at leaft 13679 Parts of the Space it would poffefs in Vacuo: And if the fame Air be condens’d by Art, the Spaceit will occupy, when moft dilated, will be as s05000to 1, to that which it poffeffes when condens’d: And Dy. fuggefts, that we arefar from knowing the utmoft it is capable of. Nor does this Power ap capable by any Means to be deftroy’d or diminifh’d: For Mr,Boyle made feveral I xperiments to difcover howlong Air, brought to the greateft Degree of Expanfion he could reduce it to in his Air Pump, would retainits Spring, and could never obferve any fenfible Diminution; altho’ the Air was cloge’d fome Months with a Weight that one would admire howit fhould fupport one Moment. It is, indeed, a wonderful Property in Ar, hinders them from flying off. that it fhould be capable of being contracted 4. The Airis elaftick. Elafticity is a Quality whereby a Body yields to any external Impreffion, by contracting itfelf into lefs Compais; and upon removing or diminifhing the and extendedinfinitely ; but, as has been faid, impreflive Power, returns to its former Space tion of a new Weight it will contraét farther, and by taking the Weight awaywill expand farther. This wonderful Property has given Occafion to feveral learned Perfons to examine into the or Figure: And by this Quality, the ir is diftinguifh’d from all other Bodies in the At- mofphere; neither Fire nor Exhalations ap- pearing to be elaftick, at leaft in any notable Degree. ‘That there is fuch a Quality in the Airis it does not appear, byall the Experiments yet try’d, that there are any Limits ofits Com- preffion or Expanfion ; but ftill by the Addi- Structure of the ir, or Figure of its Par- ticles, and to form fome Conception or Idea evident from innumerable Experiments; and as to the Structureof it, this Propertyis infeparable from it: A BladMr. Boyle conceives the ir to be a Congeder full blown being fqueez’d in the Hand, ries of minute Flo/culi, all{pringy, expanfible, the included Air maybe fenfibly perceived to and contractible, and fuppofes it to derive refift the Touch; fo that upon ceafing to its elaftick Force from its Struéture, or the comprefs it, the Cavities or Impreffions which Form of thefe Flofculi, which ‘he refembles to were made in its Surface are immediately ex- Fleeces of Wool: Whichif feveral Fleeces be pandedagain and filled up. laid one upon another, and they be comprefs'd Alfo thin Glafs Bubbles, or Bladders full of by the Hand, or any Weight, have anelaftick Air, and exactly clofed and put into the Receiver of an 4ir Pump, the Air being exhaufted out of the Receiver, the Glafs Bubbles fly in Force, and upon the Remoyal of the Preflure, but a verylittle Quantity of Air included in it, be put into a Receiver, and the Air ex- Subftances, Confiftences, Lengths, and Thick- will rife again. Others refemble the Particles of the ir Pieces by the Force of the ir included in to the Springs of Watches coil’d up, and enthem. deavouring to reftore themfelves, Again, if a Bladder quite flaccid, having Others to very flender Wires of different haufted out of the Receiver, the Bladderwill ie as the Air is exhaufted, till it be quite ul. neffes ; in greater Curls, or lefs; nearer to, or remoter from each other, €%c. yet all con- tinuing {pringy, expanfible and compreffible. Others compare them to thin Shavings 0 This Nifus, or Endeavour to expand itfelf, different Kinds of Wood, various in theit is always exerted by every Particle of “ir ; Length, Breadth and Thicknefs. and thusftrives againft an equal Endeavour of Sir Sir d/aac Newton confiders Air, as to the Ef- upon every fquare Inch. Henceit prevents, feéts alone, without concerning himfelf as to e.g. the arterial Vefféls of Plants and Anithe Figureofits Particles, and obferves, that mals from being too much diftended by the thefe aerial Particles exert certain new Powers Impetus of the circulating Juices, or by the in approaching nearer each other, whereby elaftick Force of the Air fo plentifully lodg’d they mutually endeavourto recede or fly from in the Blood of one, and the Sap ofthe other. each other: So that the farther they are apart, For, this Force does act the lefs ; and theftronger, The 4ir preffes equally every Way, as is the nearer: And he brings the Inftance of Air confirmed in what we obferve of foft Bodies and Vapours, which feem to difcover fome fuch fuftaining this Preffure without any Change of repelling Power, as an Argument of the fame Figure, and brittle Bodies without their Power's being found in other Bodies, Tho’ either of thefe Hypothefes may be fufficient, yet the former affumesortakes the more for granted ; fince it fuppofes the Air to be fleecy ; whereas, according to the latter, les of the Air may be of any Figure e, provided they are but allow’d the Vis recedendi ; but fome who have moft accurately and ingenuoufly confider’d it, have fed, that they do not know what the Air is. 3. Air rarefies by Fire, and contracts by Cold. e colder the 4ir is, the lefs Space it takes up; and, on the contrary, the warmer the Air is it poffeffes, the larger the Space ; and fo Cooling and Compreffion have the fame ffects upon Air; and fo Cold and Compreffion keep Pace with one another, The fame holds of warming and diminifhg of Weight, or Heat and Expanfion, which go Hand in Hand. ~ And to the fame elaftick Power beforemention’d, and its being expanded by Heat, ir is owing, that ir inclofed in Glafs Vet fels, at a time when it is much condenfed, 1en it afterwards comes to expand by afarDegree of Heat, frequently burfts the breaking. Air is a principal Caufe'of the Vegetation of Plants, an Inftance of which we have from Mr. Ray, in the Philofephical Tranfaétions, of Lettice-Seed, that was fown in the Glaf$ Re- ceiver of the Air Pump, which was exhaufted and clear’d from all Air, which grewnotat all in eight Days Time; whereas fome of the fame Seed that was fownat the fame Time in the open 4r, was rifen to the Heighth ofan Inch and an half in that Time; but the “Zr being let into the empty Receiver, the Seed grewup to the Heighthof two or three Inches in the Space of one Week. Another Inftance of the Ufefulnefs of the 4ir in Vegetation, is the Sedum, which will puth out Roots without Earth and Water, and live for feveral Months: And fome Sorts of Aloes, if hung upin a Roomintirely fecur’d from Frofts, will remain freth for fome Years, tho’ they will fenfibly lofe in their Weight. Airis capable of penetrating the porous and fpongy Parts of Plants, and being there contracted, and dilating irfelf again. The Air operates alfo within the Bowels of the Earth, and byits Subtilty perfpiring thro’ the Pores, affifts in the Rarefaction ofthe Cru- dities of the Earth, andin the difpelling all fu- perfluous Moifture, entering into the very Pores and Veins of the Trees, Plants, Herbs, &c. carrying along with it thofe Salts contain’d eitherin itfelf, or lodged in the Earth ; which Salts or Juices are alter'd according to the feveral Figures or Dimenfions ofthe different Strainers or Veffels of thofe feyeral Plants which Jer’d, as it is prefs’d with a lefs Load of grow upon thefame Spot ofEarth, which is ibent Ar, muft expanditfelf more. And fo impregnated with thefe Salts: And thence > it is, that Barometerical Experiments thofe Varieties in Tafte and Smell proceed, on the Tops of the higheft Mountains, notwithftanding theyall receive their Nourithare frequently very wavering and precarious. ment from the fame Stockthat is lodg’d in the 6. dir is compreffible by a Weight laid Earth. thereon, and rifes and reftores itfelf upon a The ir alfo affeéts the Branches, Leaves, Removal of the fame. This properly has been and Flowers of Trees, Plants and Herbs, enfufficiently fhewn by what has been faid be- tering and perfpiring thro’ them, and even fore, and efpecially under the Head of Elafti- through the Bark and Bodyofthe Tree ; and herefore, hay confidered the Pro- by the fame Kind ofSubtilty it does, by its e Notice of fome of refrefhing Breezes, moderate the Intenfenefs of its Operati the Sun-beams, cooling, chearing, blowing, Veg opening and extending all the Offspring of eing heavy -Nature. andpreffes all the Bodies thereon The Ar fixes and infinuates its aerial SubForce, equal to what they would {tance into the liquid Sap of Vegetables, and as the Preffure of a Column of29 all the Agitations in Nature proceed fromthe Inches D of Mercury, or 32 Feet of Water, Contrariety of Parts inhabiting together ; fo, and conf 1 s them down witha in this aerial and liquid Sut ces being mix’d, Force amounting ording to the Computa- caufe this Agitation and Motion in Ve zetables, tion of Mr or, more properly, fet it all intoa Ferment ( whether it be in the Roots or in the Ste F Perfons who have travelled the itains, agree, that the iris colder Places than near the Surface of the 1; and, of Confequence, the Air there contract itfelf more in Proportion; yet ithftanding the Air of the fame Places |