[]AN ESSAY Concerning the Effects of AIR on HUMAN BODIES.

CHAP. I. Of the Contents of the AIR.

I. AIR is that thin Fluid which ſurrounds the Earth in which we move and breathe. Air is not viſible. What we ſee in the Stream of Light let in by a ſmall Aperture into a Room, is not Air, but Duſt, and other Bodies floating in the Air. Air is ſenſible to the Touch by its Motion, and by its Reſiſtance to Bodies moved in it.

[2] II. Air is the principal Inſtrument of Nature in all its Operations on and with⯑in the Surface of the Earth, except Magnetiſm and Gravity. No Vegetable nor Animal, terreſtrial nor aquatic, can be produc'd, live, or grow, without Air. Eggs cannot be hatch'd, nor Vegetables grow in a Void. Water, purg'd of Air, will not make Plants vegetate, at leaſt very ſlowly, and that only by ſome Quantity of Air that is left in the Wa⯑ter. Air is the chief Inſtrument in the Oeconomy of Foſſils; all Operations, natural and artificial, on Foſſils, depend upon Air; for without the Aſſiſtance of Air, Fire and Heat ceaſe. In a word, Air is the principal Inſtrument in the Generation, Accretion, Reſolution, and Corruption of all terreſtrial Bodies; for it enters into the Compoſition of all Fluids and Solids, all of which gene⯑rate or produce Air in great Quantities: Oak has generated ⅓ of its Weight in Air, Peaſe as much, Indian Wheat ¼; Subſtances oily and tenacious either do not produce it ſo much, or part not with it ſo eaſily; as Honey, which does not yield 1/9; or Bees-wax, which yields 1/16; Minerals yield a great Quantity of Air, New-Caſtle Coal ⅓ of its Weight, Antimony about 28 times its Bulk, acid Spirits in So⯑lution [3] of Metals generate great Quanti⯑ties. Thoſe who deſire to know more of this Subject, may conſult the Vegeta⯑ble Staticks of the ingenious and indu⯑ſtrious Mr. Hales. Animal Subſtances are replete with Air more than any o⯑ther. Blood will generate 33 times its bulk of Air; and ſolid animal Sub⯑ſtances yield more Air than the Fluids; a human Calculus, or Stone, yields more than 645 times its bulk of Air; but of this more afterwards. At preſent we will briefly enumerate the moſt conſider⯑able Contents of this wonderful Fluid. The Air near the Surface of the Earth, in which all Animals live and breathe, contains the Steams, Effluvia, and all the Abraſions of Bodies on the Surface of the Earth, when they are ſo ſmall and light as to float in it; from whence it is evident, that the Contents of it muſt be different in different Places of the Surface of the Earth.

III. I ſhall not enter into a Diſpute about the Nature of Fire; but if it be an Element that pervades all the Space of the Univerſe, as the learned Boer⯑haave imagines, Air muſt contain its Proportion of this Element.

IV. Air contains Water which is daily exhal'd, and daily falls from the Air; a [4] Surface of Water, expos'd to the Air, evaporates an Inch in 13 Days; a Sur⯑face of Earth, with a Summer Heat, evaporates about an Inch in 40 Days; which Water, when the Air is over⯑charg'd with it, is return'd again, and falls upon the Surface of the Earth in Rain and Dew, which, by Obſervation in this Part of the terraqueous Globe, at a Medium, in a Year makes about 22 Inches of Rain, and 2½ Inches of Dew; the Dew falls chiefly when the Sun is down, and near double the Quantity in a Winter of what falls in a Summer's Night. Thus it is plain, that there is a great Quantity of Water conſtantly floating in the Air; and ma⯑ny other Experiments demonſtrate the ſame.

V. Fix'd alkaline dry Salts attract, and are diſſolv'd by the watery Particles of the Air, ſo as to increaſe in Weight from 34 to 57 in three Days; and this Effect may be carried on ſo as to qua⯑druple the Weight, 1 Ounce of Salt of Tartar making 4 Ounces of Oil of Tartar, per deliquium, only by Attrac⯑tion of Water from the Air; reckoning a cubical Inch of Air to weigh 2/7 of a Grain, the additional Weight of 3 Ounces would make 5040 cubical Inches [5] of Air, near 3 cubical Feet. There are many Conſequences, which ſeem Para⯑doxical, to be drawn from this Experi⯑ment; for Example, that the moſt pon⯑derous of Liquors, except Mercury, ſhould be made of Salt and Air; that of Salt and Water, drawn from the Air, there ſhould be made a Liquor of great⯑er ſpecifick Gravity than the Mixture of the Ingredients; for the Oil of Tartar per deliquium is in weight to Water as 7 to 5; and one Part of Salt of Tartar, with three Parts of Water, will make a Liquor which is to Water as 6 to 5. What naturally follows from the Expe⯑riment is, that either there is a great Quantity of Water in the Air, or that the Water attracted by the Salt is drawn from a great Quantity of Air.

VI. The Air is, perhaps, moſt charg'd with Water when it is clear; for when the Air is heavieſt, the Vapours aſcend the higheſt; but when they are higheſt, they are more eluted, and better mix'd with the Particles of Air; they aſcend at leaſt as high as the Tops of the higheſt Mountains, by the Clouds and Snow that are ſeen there, and where the Vapours often form Springs; when the watery Vapours turn a little heavier than the Air, they gather into Smoke or [6] Clouds, which, when their Weight can⯑not be any more ſuſtain'd by the Air, fall down in a thin Rain; and theſe Particles, by falling from greater Heights, unite, and form great Drops of Rain; and when frozen by the extreme Cold⯑neſs of the Air, Snow and Hail; but the Manner of Generation of theſe Fruits of the Air, is foreign to my preſent Sub⯑ject. When by the Weight of the Air the Vapours aſcend higheſt, and are moſt intimately mix'd with the Air, the lower Region in which we breathe may be ſaid to be dry in reſpect to human Bodies.

VII. Dew is another Ingredient of Air. Dew is not mere Water, but a Compoſition of all the watery, volatile, oily, ſaline Vapours, which exhale from the Earth, which, as long as they are agitated by the Sun, are not to be ſeen, but as ſoon as the Air cools, they be⯑come viſible. The Air being a rare Bo⯑dy, cools much ſooner than the Earth, which continues ſtill to ſweat out this Subſtance after the Sun is down; and by the Cold of the Night a great deal of it falls down again in the Form of Water; for you may obſerve, when there is no Wind, there is always to be ſeen a Coat of this Vapour near the [7] Surface of the Earth. This Dew is a Collection of all the Subſtances that tranſpire from that Spot of Earth, and conſequently very different in different Places, which is the Reaſon (as the learned Boerhaave obſerves) that the Chymiſts can never agree about the Con⯑tents of it, becauſe their Experiments are made upon the Dews of different Places, and conſequently of different Contents. In ſome Places it contains highly volatile and exploſive Particles, ſo that in Diſtillation it has broke the Glaſs; in others, it has ſtain'd the Glaſs with the Colours of the Rainbow, which nothing could take out. May-Dew, being let ſtand to putrify, will gather a fat Subſtance like Cream a-top, with Vegetables and Inſects of different ſorts; the Seeds of the one, and Eggs of the other being exhal'd. There is an Account of Dew falling, in ſome Places, in the Form of Butter, or Greaſe, which grows extremely foetid^*, ſo that the Analyſis of the Dew of any Place may perhaps be the beſt Method of finding ſuch Contents of the Soil as are [8] within the Reach of the Heat of the Sun.

VIII. The Air likewiſe contains the watery Exhalations, with the fragrant and volatile Spirit of all Vegetables. Spicy Odours are ſmelt at great Diſtances from the Countries where the Spices grow. The Quantity of theſe Exhalations of Vegetables muſt be very conſiderable in Summer. By Experiments of the moſt ingenious and induſtrious Mr. Hales,

Which is, at a Medium, 1/161 of an Inch in a Day, or a whole Inch in 161 Days, the Duration of the Summer. By an Experiment of the ſame inge⯑nious Gentleman, a Hop-yard of an Acre of Ground perſpires as much as would cover the whole Acre, an Inch in 101 Days. An Inch of this perſpi⯑rable watery Subſtance rarify'd into Air, would make (as one might call it) a vegetable Atmoſphere of 71 Feet high. In the Summer the Ground is cover'd over with Vegetables; even the Graſs expoſeth a great Surface to the Sun, [9] and is not without Perſpiration. The Heat ariſing from vegetable Perſpiration is very ſenſible in a hot Day near a Field of Corn. Upon this ſingle Ac⯑count of the Perſpiration of Vegetables, the Air of the Summer muſt be very different from that of the Winter. The Odours of ſome Plants have very ſen⯑ſible Effects upon many People. The Oils, Salts, Seeds, and the inſenſible Ab⯑raſions of Vegetables float in the Air. The Production of Plants in ſome Places, where the Plants were not indiginous, has puzzled Philoſophers; perhaps it may be accounted for, from the two Methods of propagating Plants, the Seed and the Slip, both may float in the Air; as the Bigneſs of the Slip from whence the Plant is propagated is not determined, who can ſay but the inſenſible Abraſions of a Plant may produce it? This by the way.

IX. Earth is another Content of the Air; Earth, calcin'd, flies off into the Air; the Aſhes of burning Mountains, in Vulcanos, will be carried to great Diſtances.

X. Salts of all kinds are another In⯑gredient of Air; fix'd foſſile Salts may be digeſted, render'd volatile, and eva⯑porate in Air. Markaſites attract vi⯑triolick [10] Salts from the Air. Vitriol Stones muſt be expos'd to the Air to produce Vitriol. Alum, robb'd of its Salt, recovers it in the Air. There may be obtain'd nitrous Salts from old Walls, in moſt Places; the Air either ſupply⯑ing theſe Salts as an Ingredient, or pro⯑ducing them as an Agent. In ſome Countries the Air will corrode the Bricks and Tiles. In Places abounding with Markaſites, vitriolick Salts diſperſe them⯑ſelves through the Air, which has been obſerv'd to rot the Hangings of Rooms, and lie upon the Surface of the Ground like a white Effloreſcence. There are in the Air likewiſe the Particles of all Minerals; Gold, the heavieſt of them, can be render'd volatile, and Quickſil⯑ver likewiſe. ^* All the Fumes which are rais'd by natural or artificial Fires vaniſh into Air. The poiſonous Steams of Mines produce the ſame Effects as they would do in Diſtillations. All the Smoke of culinary Fires, and Steams of fermenting Liquors, vaniſh in the Air, and make up a Part of the Contents of that in which we breathe.

[11] XI. Another Ingredient of the Air is the perſpirable Matter of Animals, the Perſpiration of a Man is about 1/34 of an Inch in 24 hours all over the Surface of the Body; conſequently one Inch in 34 days. The Surface of the Skin of a mid⯑dle ſiz'd Man is about 15 ſquare Feet, conſequently the Surface of the Skins of 2904 ſuch Men would cover an Acre of Ground, and the perſpir'd Matter would cover that Acre of Ground 1 Inch deep in 34 days, which rarify'd into Air would make over that Acre an Atmoſ⯑phere of the Steams of their Bodies near 71 Foot high. The great Quantity of Animal Subſtances, which are in the Air, appears further from this, that all Ex⯑crements and all the Carcaſes of Animals vaniſh into Air, of thoſe that are burnt very ſoon, of thoſe that are expos'd later, of thoſe that are buried in length of time; but all the Parts of the Car⯑caſes at laſt vaniſh into Air, except per⯑haps a ſmall Quantity of Bones into Earth. Eggs of Inſects float in the Air^*. Fleſh hung up by a Thread, where no Fly could come, was filled with Mag⯑gots. The Caterpillars and other Inſects, [12] which ſo ſuddenly eat up the Leaves of Trees, perhaps are produced by the Eggs of thoſe Inſects floating in the Air; at leaſt one does not eaſily perceive how they could be lodg'd in the Plants them⯑ſelves. In Africk there are Showers which affect the Bodies of Men with Rigors, the Drops are found to have Inſects in them; and perhaps there are Inſects in the Air inviſible to human Eyes: One may obſerve in that part of a Room, which is illuminated with the Rays of the Sun, Flies ſometimes darting like Hawks, as it were upon a Prey.

XII. Sulphurs ariſe from many Parts of the Earth in great Quantities; in Mines there are Fumes ſtinking, oily, In⯑flammable. Theſe ſulphurous Exhalations combin'd with ſome Salts or mettalline Particles produce Exploſions, and all the Effects of Gunpowder in Earthquakes, Thunder, &c. There are Inſtances after Thunder of ſulphurous burning Showers; ſome of theſe ſulphurous Steams ſeem to riſe by a projectile Motion to great Heights, ſo they do likewiſe in vacuo with a great Celerity. This appears by Meteors, ſuch as that in the Year 1718, which Dr. Halley has prov'd by Obſerva⯑tions to be 60 Miles high, of a Mile Diameter, and run 300 Miles in a Mi⯑nute: [13] There muſt have been Air to pro⯑pagate the Sound of the Exploſion of that Meteor which was heard in ſome Places. Tho' the Air at that Height was 30000 times rarer than that near the Surface of the Earth, it ſeems it was ca⯑pable of producing Sounds. The Coruſ⯑cations which have often of late appear'd in this Country, ſeem'd to be of the ſame Nature, particularly that remarkable one 1716. In thoſe Coruſcations one might obſerve the ſulphurous Steams riſe from the Earth with a projectile Motion, to a great Height, and being conſum'd, have not diſcover'd any ill Effect upon human Bodies.

XIII. The Air near the Surface is charg'd with all thoſe heterogeneous Parti⯑cles, and many others not poſſible to enumerate; and yet the wiſe Author of Nature has temper'd this heterogeneous Mixture, ſo as to make it ſalubrious to the Animals that live in it, except in a few accidental Caſes; and perhaps pure Air without any of thoſe Contents is un⯑fit to ſuſtain Animals and Vegetables. To make this Element wholſom, the wiſe Author of Nature has ſo order'd that the whole Maſs is never overcharg'd with thoſe Contents. For Example, ſince hu⯑man [14] Bodies are ſo contriv'd, as not to bear Exceſſes of any kind, as too much Drineſs, or too much Fluidity, there is a conſtant Circulation of the Water in the Air, and the Air of any Place contains very near the ſame Quantity of it. The Action of the Sun, or the Sum of all its Force upon the ſame Surface of Land and Water, and the Heat of the Surface of the Earth within the Year, is pretty near uniform, and conſequently the Quan⯑tity of Evaporation the ſame: The Air has a Power of imbibing and ſuſtaining only a certain Quantity of this Water, and the Sum of the Quantity that falls from the Air over the whole Surface of the Earth, in Rain, Snow, or Hail, is the ſame, tho' by accidental Cauſes of Winds, and the Stoppage of the Clouds, by Tracts of Mountains, more of theſe Vapours may be carried, and fall in one Place than another. This Water is again carried by its natural Gravity in Streams to the Sea, and other Reſervoirs of Water, and from thence again exhal'd; only there is left a ſufficient Quantity for the Nutrition of Plants and Animals; the Moiſture of whoſe Bodies is again ex⯑hal'd, and this Circulation is conſtantly maintain'd; only there remains one Doubt, that the ſolid Parts of Animals, [15] Vegetables, and perhaps of Foſſils, be⯑ing moſtly produc'd from watery Fluids, and ſome Quantity of thoſe ſolid Parts, not being by the common Powers of Nature, convertible again into Water, whether the Solids of the Earth do not gain upon the Fluids, the firſt increaſing and the ſecond decreaſing? The Oeco⯑nomy is the ſame in the other Contents of the Air; the perſpirable Matter of Vegetables and Animals, the Oils, Salts, and Sulphurs fall down again, and repair the Bodies that are on or near the Sur⯑face of the Earth.

XIV. Nature makes uſe of all poſſi⯑ble ways, to preſerve this heterogeneous Fluid in a wholſom State. The Ingre⯑dients are digeſted and attenuated by Heat; they are ſtirr'd and conſtantly agitated by Winds, which mix the Air of different Regions together; there are Fermentations ſucceeded by violent Mo⯑tions and Exploſions, in Lightning and Thunder, and imitable by the Mixture of like Ingredients in Chymical Opera⯑tions. In thoſe Storms the redundant and noxious ſulphurous Particles are con⯑ſum'd. There are Inſtances of ſome Places becoming habitable by Earth⯑quakes and Inundations, that were not ſo before: The Perſpiration of the Earth [16] is by turns ſtopt, and reſtor'd; there are Congelations of the redundant Water Precipitations, and many other Operati⯑ons unknown to Art, producing a great Variety of Effects. Air is the Inſtrument of all thoſe Operations when perform'd by Art; and thoſe heterogeneous Bodies act upon one another in the Air it ſelf, by many unconceivable ways: Many Experiments and Obſervations demon⯑ſtrate the mutual Action of Bodies floating in the Air upon their approach. Some Chymical Proceſſes will ſucceed in one ſort of Air; which will be attempt⯑ed in vain in another: Tartarus regenera⯑tus can be made only in a Laboratory, where they diſtil Vinegar. It is impoſſi⯑ble to conceive the Reſult of all ſuch O⯑perations in a heterogeneous Mixture; Mankind may be ſenſible of their Effects, but can never know their Nature.

XV. Tho' Nature preſerves the Maſs of this Fluid in a wholſom State; it muſt neceſſarily happen, that the Air of particular Regions, Seaſons, and Places may differ very much in their Proporti⯑ons of the Mixture of the Ingredients enumerated; and ſuch Air muſt affect human Bodies variouſly by ſuch Exceſſes or Defects. Too great Moiſture affect hu⯑man Bodies with one Claſs of Diſeaſes, [17] and too great Drineſs with another: The Powers of Human Bodies being limited and intolerant of Exceſſes of any kind. Air replete with the Steams of Ani⯑mals, eſpecially of ſuch as are rotting, has often produced peſtilential Fevers in that Place, of which there are many In⯑ſtances, as that mention'd by Ambroſe Paree 1562, rais'd by Carcaſes thrown into a Ditch. Such have likewiſe been rais'd by great Quantities of dead Lo⯑cuſts, and by dead Whales. The Steams of great Quantities of corrupted Vegetables have produced the ſame Effects in their Neighbourhood. The Effluvia of hu⯑man live Bodies are extremely corrup⯑tible; the Water in which human Crea⯑tures bathe, by keeping, ſmells cadave⯑rous by N. xi. of this Chapter, leſs than Three Thouſand human Creatures living within the compaſs of an Acre of Ground, would make an Atmoſphere of their own Steams about 71 Feet high, which, if not carried away by Winds, would turn peſtiferous in a moment; from whence it may be inferr'd, that the very firſt Conſideration in building of Cities is to make them open, airy, and well perflated. Peſtilential Conſtitutions have been often preceded by great Calms; from hence the Air of Priſons produceth [18] often mortal Diſtempers; and Ships Crews turn ſickly in Bays and Harbours, which would be healthy in the open Sea: It ought to be the principal Care of ſuch as attend Hoſpitals to give a thorough Paſſage to the Air. Since the putreſcent Parts of Carcaſes buried under Ground, by N^o xi. are carried off, tho' ſlowly into the Air: Whether this is not an Objection againſt Burying in Churches? And whether it is not proper that all Burying Places ſhould be without Cities in the open Air? By what was obſerv'd N^o viii. the Air of the Summer differs conſiderably from that of Winter. In Summer the Air is replete with the per⯑ſpirable Matter of Vegetables, abound⯑ing with volatile Spirits and Oils, which perhaps ſtimulates and exhilirates the Spirits; and that of ſome Plants is too powerful for ſome People, who cannot ſupport the Smell of ſome of them.

XVI. It follows from Obſervations, N^o xi. That the Air of great Cities differs conſiderably from that of the Country. There is more of the perſpi⯑rable Matter of Animals, which is never entirely blown off; there is more of the Steams of culinary Fires. There is a ſmaller Perſpiration of the Ground, by the Paving of the Streets, and conſequently, [19] as the Steams are hurtful or wholſom. Leſs Effect from them in either Caſe; tho' the Air of the Country is brought into Cities by Winds, there is always leſs of the Steams of Vegetables in Cities than in the Country.

XVII. Of all Contents of Air none are more noxious to human Bodies than Sulphurs: The Steam of Charcoal ſuffo⯑cates in a Moment, therefore when ſul⯑phurous Steams are too redundant, na⯑ture ſets them on fire by Lightning: Some People are ſenſibly affected by the Air, before Thunder and Hurricanes. In hot Countries the Benefit which the Inhabitants receive from Thunder-Storms abates the Terror of them. There are ſul⯑phurous Vapours which infect the Vege⯑tables, and render the Graſs unwhol⯑ſom to the Cattle that feed upon it^*: Miners are often hurt by theſe Steams. Obſervations^† made in ſome of the Mines in Derbyſhire, deſcribe four ſorts of thoſe Damps. The firſt the Mi⯑ners call the common ſort, perceiv'd at firſt by the Candles burning Orbicular, and the Flame leſſening by Degrees, the [20] Effects of it upon human Bodies are Fainting, Convulſions, Suffocation; the ſecond, is what they call the Peaſe-bloom Damp; which the Miners imagine is the Steam of a Vegetable, growing lower than the Level; the third is the moſt noxious: The Miners tell you, they ſee in the higheſt Part of the Roof, in thoſe Paſſages which branch out from the main Groove, a round thing of the Bigneſs of a Football, with a Film or Skin about it, which when broken by accident, diſperſeth it ſelf and ſuffocates all the Company. The Miners, who are but coarſe Philoſophers reckon that is the Steam of their own Bodies; which is not impoſſible, for the Oil of this Steam may poſſibly produce this Film or Coat. The fourth is the fulminating Damp, re⯑ſembling in its Nature and Effects Gun⯑powder, or that Matter which produceth Thunder; when this takes Fire it kills by Exploſion as Thunder and Gunpow⯑der: The Remedies of the Miners, are the ſame, which Nature uſeth in like Caſes, making Communication with the whole Maſs of outward Air, by Shafts, Per⯑flation with artificial Winds and Bel⯑lows, and ſetting fire to thoſe ſulphurous Steams, after which they are able to go on with their Work: There are like⯑wiſe [21] in ſome deep Wells and Pits ſul⯑phurous Steams, which will take Fire with a Candle; in ſome the Sulphur is combin'd with Sal Ammoniack, which does not fulminate. Sulphur it ſelf is not unfriendly to the Lungs; and the Exhala⯑tions from ſulphurous Spots of Earth in the open Air, are recommended as whol⯑ſom as the Air about the City of Na⯑ples; but it muſt be conſidered, thoſe are in the free and open Air, not too re⯑dundant, and perhaps unmix'd with o⯑other noxious Salts, which thoſe above-mention'd may be replete with; it will appear in the following Part of this Diſ⯑courſe, that Sulphur deſtroys the Elaſti⯑city of the Air.

XVIII. Metalline acid Salts which perſpire from certain Spots of the Earth, and by their Gravity riſe only to a cer⯑tain Height, are extremely noxious taken in by the Breath; they contract the Veſi⯑cles, or immediately coagulate the Blood in the Capillary Veſſels, which creep along the Surfaces of the Veſicles of the Lungs, which have very thin Coats, and are in immediate Contact with the out⯑ward Air; ſuch is that mortiferous Steam in the Grotto del Cane near Naples.

XIX. Some have imagin'd the Plague to proceed from inviſible Inſects. This [22] Syſtem agrees with many of the Appea⯑rances in the Progreſs or Manner of Propagation of that Diſeaſe; but is alto⯑gether inconſiſtent with others. Theſe are a few obvious Inferences, relating to our Subject, drawn from the Conſidera⯑tion of the Contents of the Air; and conſidering it as a heterogeneous Body, many others of the ſame kind may be made, which the Brevity in this Eſſay will not admit: I proceed to the Conſide⯑ration of the Properties of the Air.

CHAP. II. Of the Properties of Air.

I. THE firſt Property of Air is Fluidity, which by no Power of Art or Nature yet known can be de⯑ſtroy'd; it preſerves its Fluidity in Cold 44 Degrees greater than any Natural Cold: The Sparkling, which Boerhaave obſerv'd in Air illuminated by the Rays of the Sun, and which he at firſt ima⯑gin'd to proceed from ſome Congelation of the Air, he afterwards diſcover'd to proceed from watery Particles floating in the Air. No Condenſation, Fermenta⯑tion, [23] nor Coagulation of Mixtures, where Air reſides, have ever deſtroy'd its Flui⯑dity, which Quality is abſolutely neceſ⯑ſary to an Element, in which Vegetables and Animals grow. No Vegetable nor Animal can expand its Fibres, in their Natural Figure, but in a Fluid that re⯑ſiſts equally the Elongation of its Fibres: The Preſſure of the Atmoſphere keeps both Vegetables and animal Fibres within certain Limits of Accretion; it being always Fluid, the Preſſure is equal upon every Part of their Surfaces. There⯑fore if you would give a human Creature the due Figure which Nature affects, it muſt be kept as free as poſſible from the Preſſure of any hard Body: Human Crea⯑tures by being a great Part of their time upon their Feet, which is but a ſmall Part of the Surface of the whole Body, acquire a better Shape, and the Feet by bearing the Preſſure of the whole Body grow Callous; if a human Creature were always recumbent it would not take its Natural Figure. Confinement by Stays or ſtrait Clothes muſt ſpoil or change the natural Shape: Water being a Fluid much denſer than Air, admits, ſupports and keeps together the Bodies of larger Animals than Air can do.

[24] II. The Particles of Air are not diſcernable by a Microſcope, tho' they may be larger than the Particles of Light; they do not reflect it in viſual Angles.

III. Notwithſtanding the Minuteneſs of the Particles of Air, many denſer Fluids will paſs where it cannot; Oil will enter through Leather, which excludes Air.

IV. Lubricity or Diviſibility by the ſmalleſt Force, is another Property of Air, by which Animals move in it, without much Reſiſtance; if there were Experiments of the Swiftneſs of the Motion of Birds and Fiſhes, one could determine the Proportion of their Force. Birds and Fiſhes move through their re⯑ſpective Element after the ſame manner: Fiſhes are the Birds of the Water. Fiſhes paſs through an Element 800 times denſer than Air, upon which Account they muſt employ a Force proportional to the greater Reſiſtance of the Medi⯑ums: on the other hand a great Part of the Force of Birds is employ'd to ſup⯑port their Bodies in a much rarer Me⯑dium, whereas the Bodies of Fiſhes are equilibrated with the Water in which they ſwim. Yet the Air has ſome Degree of Tenacity, whereby the Parts attract one another, as appears by the ſpherical [25] Figure of Bubbles, which attract and run into one another. At the ſame time by their Elaſticity the Particles of Air in o⯑ther Circumſtances ſeem to have a Power of Repulſion or Flying off from one ano⯑ther; thoſe two Properties are conſiſtent as we ſee in Light.

V. The Reſiſtance of Air is very con⯑ſiderable in Bodies mov'd ſwiftly through it, or by its ſwift Motion againſt Bo⯑dies: The Reſiſtance in the firſt Caſe increaſeth in the Duplicate Proportion of the Celerity of the moving Body, that is, the Reſiſtance is 100 times greater when the Celerity is but ten times; ſo therefore if light Bodies be moved with a great Velocity, the Reſiſtance of the Air will throw them back in another Direction. Air mov'd with Rapidity in violent Winds, has very ſenſible Effects upon human Bodies; we ſee the power⯑ful Effects of a large Surface of Air or Wind, in moving great Bodies and turn⯑ing Engines: A Stream of Air of 7 Square Feet, near the half of the Sur⯑face of a human Body, moved with a Velocity of a great Wind or 22 Feet in a Second of Time, preſſeth againſt a hu⯑man Body with a Force equal to Water mov'd 1½ Feet in a Minute, to which, if you add the Celerity of the Perſon [26] moving oppoſite, the Preſſure is very conſiderable; ſo that riding or walking againſt great Winds is a great Exerciſe; the Effects of which are Redneſs and In⯑flammation of the Parts expoſed to the Air, all the Effects of a ſoft Preſs or Ver⯑beration, Heat and Drouſineſs.

VI. Gravity is another Property of Air, whereby it counterpoiſes a Column of Mercury from 27½ Inches to 30½, the Gravity of the Atmoſphere varying 1/10, which are its utmoſt limits; ſo that the exact ſpecifick Gravity of the Air can⯑not be determin'd when the Barometer ſtands at 30 Inches, with a moderate Heat of the Weather. The ſpecifick Gravity of the Air is to that of Water about 1 to 800, and to that of Mercury as 1 to 10800. Dr. Halley's Account of the Cauſes of theſe Variations of the Gravity of the Air ſeems very ſatisfacto⯑ry; for they muſt either proceed from the Air in one Time and Place, being charg'd with greater or leſſer Quantities of pon⯑derous Contents; which, by what is ſaid in the foregoing Chapter, it imbibes plentifully, or from being accumulated more in one Place than another: The Air's being accumulated more in one Place than another, muſt proceed from the Currents of Air or Winds; thus con⯑trary [27] Currents of Air tending to the ſame Place, muſt accumulate the Air in that Place, and conſequently raiſe the Mercury in the Barometer, as a Weſter⯑ly Wind in the Atlantick, and an Eaſter⯑ly in the German Ocean: Two Currents of Air from the ſame Place, muſt ſink the Air in that Place, and conſequently the Mercury in the Barometer: This is very poſſible in Liquids, and happens even in the Motion of the Tides; if there was always a perfect Calm, the Aequilibrium could only be charg'd by the greater or ſmaller Quantity of ponderous Contents; in confirmation of this Syſtem it is found, where the Winds are not va⯑riable, as near the Line, the Alterations of the Baroſcope are very ſmall. Theſe Alterations of the Gravity of the Air cannot proceed from its letting fall its ponderous Contents, as in great Showers. It is true, that a heavy Body falling thro' a Fluid, during its Deſcent, does not preſs upon it, but by the Reſiſtance which the Fluid gives to its Motion in Deſcent; but the Decreaſe of the Weight of the Atmoſphere during the Fall of Rain, Snow, or Hail, is not proportional to this Cauſe, nor can be accounted for from it.

VII. The Air being fluid and heavy, preſſeth equally upon the Surface of a [28] Human Body, with a Weight equal to a Column of Mercury, whoſe Baſis is equal to the Surface of a Human Bo⯑dy; and Altitude, that of the Barome⯑ter, perhaps in a middle-ſiz'd Man, with a Weight of 32000 Pounds, as it is poſ⯑ſible for the Air to vary 1/10 in its Weight, ſuch a Human Body muſt be preſſed with 3200 Pound Weight more at one time than another; and if the Height of the Mercury varies only one Inch, there is the Difference of above 1000 Pounds. Such Alterations affect both the Fluids and Solids very ſenſibly; but as the Coun⯑terpoiſe between the Air within and that without the Body, is quickly re⯑ſtor'd by the free Communication that is between them, theſe Alterations are ſuf⯑fered without any ſenſible Inconvenience; and this indeed proves the ready Admiſ⯑ſion of the external Air into the Veſſels of the Body, and the Eſcape of a⯑erial Particles within the Body, in each Caſe of the Alteration of the Gravity of the external Air, from leſs to more, or more to leſs; for if this Aequilibrium was not kept between the external Air, and that within the Body, both the Fi⯑bres and Fluids being elaſtick, in the Caſe of an Increaſe of the Gravity of the ex⯑ternal Air, the Fluids and Solids would [29] be too much compreſs'd; and in the Caſe of a Decreaſe of this Gravity, would expand themſelves with a dolorous Sen⯑ſation, and Danger to the Life of the Animal. A Fall of the Mercury in the Barometer is the ſame with the Exſuction of ſo much Air in an Air-Pump, in which Caſe we perceive the Fluids and Solids expand themſelves, and the Ani⯑mal ſwells. I have obſerv'd very ſenſi⯑ble Effects of ſudden Falls of the Mer⯑cury in the Barometer in tender People, and all the Symptoms they would have felt by the Exſuction of ſo much Air in an Air-Pump: Animals in the Air-Pump are relieved of their Symptoms in a great meaſure, by voiding of Air or Wind out of their Bodies; therefore, if theſe Alterations of the Air were very ſudden, and to great Degrees, they would produce very great and troubleſome Symptoms in Human Bodies. As the Caſe ſtands now, the Variations of the Gravity of the Air keep both the Solids and the Fluids in an oſcillatory Motion, ſynchronous, and proportional to their Changes, and which, by the different Degrees of Tenſion of the Fibres, and Expanſion of the Fluids, muſt neceſſari⯑ly affect Human Bodies variouſly, and produce Alterations, of which the Inha⯑bitants [30] of Countries where the Mercury in the Barometer ſtands at the ſame Height, are not ſenſible; but of this more after⯑wards.

VIII. Air is a Fluid in conſtant Mo⯑tion: One may perceive in that Part of a Room which is illuminated by the Sun-beams entring at a ſmall Hole, the Bodies floating in the Air are in continual Mo⯑tion; a conſtant undulatory Motion is perceiv'd by looking through Tele⯑ſcopes: Theſe Undulations of the Air af⯑fect ſmall and tender Bodies, yet not ſo much as to alter their Figures; when the Air enters or eſcapes out of Bodies, it does not divide it ſelf at firſt into its mi⯑nuteſt Particles, but gathers into Bubbles; and the Nature of Air is ſuch, that the ſmalleſt Quantity of it has the Force of the whole Atmoſphere, by its Spring or Elaſticity; of which in the next Article. If Air Bubbles are generated in the Ca⯑vities of the Veſſels of Human Bodies, they muſt produce prodigious Effects.

IX. Air is likewiſe compreſſible and elaſtick: It can be compreſs'd into Spaces reciprocally proportional to the incum⯑bent Weights, and expands it ſelf again in Proportion as the compreſſing Force is remov'd: If the Weights compreſſing be as 1, 2, 3, the Spaces into which [31] the Air is compreſs'd will be as 1, ½, ¼, conſequently the Denſity of the Air will increaſe in direct Proportion to the compreſſing Weights; therefore, as you approach towards the Surface of the Earth, the Denſity of the Air increaſeth, becauſe of the greater Height of the Co⯑lumn of incumbent Air; as you go higher, the Air expands itſelf, and grows rarer, by the Force of its Spring or Elaſ⯑ticity, having ſo much of the incum⯑bent Weight taken off. Were the whole Air of equal Denſity, the Atmoſphere would not much exceed the Height of 5 Miles, and in the Aſcent of 900 Foot the Mercury would ſink 1 Inch, and ſo on: But, as I ſaid before, the Expanſion of the Air increaſing, that is, the Air growing rarer as the incumbent Weight is taken off, an Aſcent of 915 Feet from the Surface of the Earth ſinks the Mer⯑cury 1 Inch; but as you aſcend higher, it requires a greater Space of this thinner Air to make the Mercury ſink another Inch, and that is found to be 1862 Feet, or more than double the former Height, and to ſink the Mercury 3 Inches re⯑quires an Aſcent of 2844, which is more than triple of 915; the Height of 1 Mile is requir'd to ſink the Mercury 5.32, that is about 5 Inches and ⅓ of an [32] Inch; at 3 Miles high the Mercury will be reduc'd from 30 Inches to 16.68 Inches, that is 16 Inches, and near [...]/10 of an Inch, the Height anſwering to an Inch of Mercury, ſtill increaſing in a Proportion determin'd by an eaſy Geo⯑metrical Calculation; of which it would be impertinent to ſay more, becauſe it is equally uſeleſs to thoſe who do, or do not underſtand Geometry, repeating to the firſt what they know already, and en⯑deavouring to teach the others what they cannot comprehend.

X. From the different Denſity of the Air in higher or lower Regions, the ſame Effects are produced upon the Inhabi⯑tants of theſe Regions, as by the Varia⯑tions of the Gravity of the Air above-mention'd.

XI. The Elaſticity of the Air is a Force equal to its Gravity; for, as I ſaid, the ſmalleſt Bubble of Air by its Elaſ⯑ticity will counterpoiſe the whole At⯑moſphere of equal Denſity: By thoſe two Qualities of Gravity and Elaſticity, and the Variations of them, the Air pro⯑duceth great Effects upon Human Bodies; by theſe, Reſpiration is performed, and the Balance kept between the external Air and that within the Veſſels of the Body: Yet I cannot but obſerve that [33] there is ſomething very hard to be under⯑ſtood in the Gravity and Elaſticity of the Air. Suppoſe Air is in ſpecifick Gra⯑vity to Water as 1 to 800: If there be 1/800 of Water in Air, the Air it ſelf muſt weight nothing; becauſe ſo much Water is equiponderant with the ſame Quanti⯑ty of Water. I have ſeen a Summer Shower of long duration, which has filled a Tub 3 Inches perpendicular; 33 Feet of Water weighs equally with the whole Atmoſphere, 3 Inches of Water is ¼ of 1/33 or 1/132 of the Weight of the whole Atmoſphere, much more than 1/800. It would ſeem, that ſo great a Quantity of Water could not be at once in the Air of that Place, but muſt have been collected in Clouds from a great Quantity of Air. Water is mix'd with Air in the Form of Smoke, which is perhaps a Collection of Bubbles, with a viſcous Coat of Water about them, and are lighter than Air; but ſtill there is ſo much Water in the Air whatever Form it is in, beſides Water there are a great many other Contents in the Air ſpecifi⯑cally heavier than Air; if the Proportion of thoſe Contents is not extremely ſmall, Air it ſelf muſt weigh nothing. Then as to the Compreſſibity of Air, that muſt have certain Limits, and can never go [34] beyond the Quantity of Water, and other incompreſſible Subſtances that are in Air. The Rarity and Denſity of Air has likewiſe its Bounds; for if the Law of Expanſion obtain'd conſtantly, a Globe of Air of an Inch Diameter, at the Diſtance of a Semidiameter of the Earth, would fill all the Space of the Planetary Regions further than the Sphere of Saturn: As to the Denſity of the Air, ſuppoſe a Tube, or, as the Miners call it, a Shaft were ſunk from the Surface of the Earth to the Centre within the Sur⯑face of the Earth, the Gravity of Bodies is as the Diſtance from the Centre; yet according to the Laws of Denſity, by a Computation too long to inſert here, at 50 Miles deep, Air would be denſer than Mercury, and near the Centre infinitely denſer than Gold. This is an impoſſible Suppoſition; and all the Air above and within the Earth, of the Denſity of Mer⯑cury, wou'd not compoſe a Ring round the Surface of the Earth, of perhaps a Yard high. Therefore the Compreſſibility, Den⯑ſity and Rarity of the Air have Limits which they cannot exceed.

XII. True Air never loſeth its Elaſti⯑city, tho' it exerts it only when collected into a Maſs by its Elaſticity; it inſinuates it ſelf in the Spaces of Liquors not ſuffi⯑ciently [35] ſaturated with Air; and there it remains divided in its minuteſt Parts, as it were in a fix'd State; but when it is expanded by Heat, or the incumbent Preſ⯑ſure is taken off, it is collected in greater Maſſes, and exerts its Elaſticity in Pro⯑portion to the Diminution of the incum⯑bent Preſſure.

XIII. Animal Fluids and Solids con⯑tain more Air in them in Proportion than perhaps any other Subſtances. ^* Hartshorn will yield 1/7 of its whole Subſtance or 234 times its Bulk in Air. A human Calculus can be almoſt all evaporated by Fire. Animal Fluids do not contain ſo much Air as the Solids; but they contain a greater Proportion of Air than other watery Fluids. Blood contains 1/27 Part of its Weight in Air, and 33 times its Bulk; whereas 54 Inches of Well-Water yield but 1 Inch of Air: Suppoſing the Spe⯑cifick Gravity of Water to be to that of Air as 800 to 1, Water contains only 1/43200 of its Weight in Air. Briſtol-Water and Holt-Water yield much the ſame Proportion as common Water, but Pyrmont-Water double the Quantity; the Activity of Chalybeat Water is owing to [36] ſome Aerial Particles in them; when theſe are evaporated, they are inſipid and without any Virtue by the Quantity of Air, which Blood and other animal Fluids contain; they expand themſelves to a great Degree in an exhauſted Receiver. Therefore the Variation of the Gravity and Elaſticity of the Air, which propor⯑tionally expand and dilate the Liquors, with which the external Air communi⯑cates, muſt have ſenſible Effects upon animal Fluids, as Air is a principal In⯑ſtrument in all the animal Oeconomy; and therefore a principal Ingredient in the Compoſition of animal Subſtances. It muſt in a particular manner affect a⯑nimal Bodies, and variouſly by its Changes influence all their Operations. This only in general.

XIV. Air of double Denſity has dou⯑ble the Force; for if Air of a certain Denſity keeps up the Mercury in the Ba⯑rometer 28 Inches, the ſame Capacity fill'd with Air of a double Denſity will keep it up 56 Inches. Heat increaſeth the Elaſticity of the Air.

XV. The Heat of boiling Water will augment the Force of the Spring of the Air ⅓, if the Air is ſhut up; or ex⯑pand it into ⅓ more of Space if it is at Liberty; if the Air be doubly denſe, the [37] ſame Degree of Heat acts with a double Force upon it. For Example, if common Air keeps up the Mercury in the Barometer at 30 Inches, the Heat of boiling Wa⯑ter will increaſe its Force ⅓, and make it ſuſtain the Mercury at 40 Inches; but if Air is doubly denſer, the Augmenta⯑tion of the Spring by the ſame Degree of Heat would be 20 Inches, and ſuch an Air with double the Denſity, and the ſame Degree of Heat, would ſuſtain the Mercury 80 Inches, 60 upon account of its double Denſity, and 20 which is the Augmentation of ⅓ of the Force by Heat; ſo that denſer Air heated muſt have great Effects, ſuch as ſubterraneous Air in great Depths. For Example, Air 100 times denſer with the Heat of boiling Water, would have above 133 times the Force of common Air. The Heat of boiling Water will increaſe the Force of the Air, or expand it ⅓ more; but greater Heats, as that of melting Iron, ſuch as may happen in ſubterraneous Places, would produce much greater Effects. The greateſt Alteration of the Denſity of the Air, by the Difference of Heat and Cold in our Climate, does not ex⯑ceed ⅛, which is indeed very conſidera⯑ble. This by Mr. Hauksbees Experiment, but there are others, in which the Difference [38] is greater. Cold likewiſe increaſeth the Elaſticity of the Air by increaſing its Denſity or Weight, to which its elaſtical Force is proportional. We ſhall treat more fully, in the following Part of this Eſſay, of theſe Qualities of the Air, of Heat, Cold, Moiſture and Drineſs, and as they are combin'd with its Proper⯑ties of Gravity and Elaſticity, and of their Effects on Human Bodies.

XVI. By what has been ſaid of the Elaſticity of the Air, and which the ſmalleſt Maſs of it paſſeth, ſo as to be able to reſiſt the Preſſure of the whole incumbent Atmoſphere, one may per⯑ceive the great Force of hot and elaſtick Air in the Cavities of Human Bodies; whither Air-Bubbles may be generated in the Veſſels of Human Bodies, I ſhall not poſitively determine. Strong Probabi⯑lities for the affirmative are, that Air-Bubbles are apt to get into Pipes which carry any Fluid even into thoſe which carry Water; and their Effects are well known. It is likewiſe certain, and what I have known by frequent Experience, that there are Pains in the Extremities of the Body, which ſeems flatulent; and I have often perceived by Friction of theſe Parts immenſe Quantities of Wind to come out of the Stomach by Belching, [39] by which the Patient was reliev'd. Air is not ty'd to the Laws of Circulation, but will break out wherever it can have a Vent; the Force of an Air-Bubble to produce Tenſion and Pain is ſufficient. By what is ſaid,

XVII. It ſeems likewiſe probable that Spaſms and Convulſions are produced by hot and elaſtick Air, or Steams pent up. The Symptoms of Animals ſhut up in an exhauſted Receiver are Convulſions; and as ſoon as thoſe Animals have voided Air, through all the Emiſſaries of their Bodies, ſo as to bring the Air within their Veſſels to a Balance with the out⯑ward rarer Air of the Recipient, they ſeem to recover for a Moment, 'till by a new Exſuction of Air, they relapſe into the ſame Condition, as I obſerved before: Some tender human Creatures are apt to fall into Lypothymies upon a ſudden Fall of the Mercury in the Barometer, which puts them in the ſame Caſe with the firſt Exſuction of Air in the Air-Pump.

XVIII. Human Creatures can live in Air of very different Denſities; the Air in the ſame Place may differ [...]/10 in Den⯑ſity or Weight, ſo much being the Varia⯑tion of the Height of the Mercury; but what is more ſtrange, Human Creatures can live in Airs where the Difference of [40] the Denſities is double: in the Bottom of Mines, where the Mercury ſtands at 32 Inches; and at the Top of the higheſt Mountains, which ſuppoſing them to be 3 Miles of perpendicular Height, the Mer⯑cury muſt ſtand at a little above 16 In⯑ches.

XIX. Though human Creatures can ſup⯑port ſuch a Difference of Preſſure, as in the common Variation of Gravity in the ſame Place, makes the Difference of Preſſure upon a Body of an ordinary Size 3600 Pound Weight, and in the Difference of Altitude in the Bottom of Mines, and at the Tops of the higheſt Mountains, the Difference of 18000 Weight; yet ſuch a Difference of Preſſure muſt produce great Difference in the Tenſion of the Fibres, and Expanſion of the Fluids of a Human Body. In the Caſe of a greater Weight, the Fibres being more ſtrongly brac'd and the Fluids more compacted, and, as I obſerv'd before, were there not a free Communication between the external Air, and the Air within the animal Fluids, theſe Changes would be inſuppor⯑table; and the Animal would be in the ſame Caſe as in an Air-Pump with the Exſuction of half the Air; in which Caſe the Blood would boil up and ex⯑pand it ſelf to a great Degree by ſo much [41] of the Preſſure of the external Air being taken off. All this is prevented by the quick Expulſion and Admiſſion of the Air within and without the Body.

XX. It ſeems probable that the Di⯑minution of the Force of the Preſſure of the external Air, in bracing the Fi⯑bres, muſt create a Debility in muſcular Motion, which is the Reaſon that ſome People have imagined they breath'd ſhorter than uſual in aſcending the Tops of high Mountains; but the true Rea⯑ſon is, that by the Diminution of the Preſſure of the Air upon the Muſcles, leſs Exerciſe puts one out of Breath; and perhaps the Overbalance of the Air within the Thorax may have ſome Ef⯑fect. But then it may be objected, That Mountaineers are not leſs active and ſtrong than the Inhabitants of low Countries: To which I anſwer, That there are two Cauſes which hinder this Effect; the firſt is the Exceſs of Cold⯑neſs of the Air on the Tops of Moun⯑tains, above that of lower Situations, which counterbalanceth the leſs Weight, and braceth the Fibres more ſtrongly; by reaſon of this Exceſs of Coldneſs in greater Altitudes, the Decreaſe of the Denſities of the Air does not preciſely anſwer Calculation: Another Reaſon [42] ſeems to be this, That ſuch as live in a rarer Air, are habituated to the Exer⯑ciſe of a greater muſcular Strength, they are as it were in the Caſe of Birds, which, performing their Motions in a rarer Medium, muſt always uſe a great⯑er muſcular Strength, which, tho' indeed Nature has endued them with the very Habit of uſing it, muſt ſtrengthen their Fibres. A tame Bird cannot fly ſo well as a wild one.

XXI. The Preſſure of the Air upon the Lungs is much leſs than it has been computed by ſome; but ſtill it is ſome⯑thing, and the Alteration of [...]/10 of its Force upon the Lungs muſt produce ſome Difference in elutriating the Blood as it paſſeth through the Lungs, which are the chief Inſtruments of Sanguifica⯑tion. The Variations of the Preſſure of the Air, in its Gravity and Elaſti⯑city, muſt produce proportional oſcilla⯑tory Motions in the Fluids and Solids of Human Bodies; and when the Ex⯑curſions are extreme and frequent, ſuch great Agitations of the Fluids and So⯑lids may produce great Alterations in Human Bodies; for which there is no need to have Recourſe to occult Qua⯑lities in the Air. There's a Sort of Tor⯑ture (if I remember right) uſed by the [43] Inquiſition, which, by ſweathing the Bo⯑dy very hard, and immediately un⯑bracing it, will produce a moſt exqui⯑ſite Pain and feveriſh Symptoms. The Air, by the Softneſs of its Contact, does not hurt animal Fibres much, but the bracing and unbracing the Fibres ſtrong⯑ly by Turns may produce Changes ana⯑lagous to this Torture; and ſuch Alter⯑ations are producible not only by the Variations of the Gravity and Elaſticity, but by the Qualities of Heat, Cold, Moi⯑ſture, and Dryneſs; of which I ſhall ſay ſomething in the following Chapter.

CHAP. III. Of the Qualities of the Air.

I. I CALL Fluidity, Gravity, Elaſti⯑city, &c. Properties of the Air, re⯑ſiding conſtantly in the whole Maſs, and every Part of it. Heat, Cold, Dryneſs, and Moiſture, I chooſe to term Qualities, becauſe, taken in the vulgar Senſe, they are variable, and do not conſtantly in⯑here in the Whole, nor in the Parts.

II. The Air, by theſe variable Quali⯑ties of Heat, Cold, Dryneſs, and Moi⯑ſture, [44] muſt neceſſarily produce great Va⯑riety of Changes in Human Bodies. Let us conceive a Fluid permanently warm, as Human Blood, inclos'd in a Syſtem of Tubes, thin, flexible, to which the outward Air has admittance by innumera⯑ble Paſſages: Let us conceive this Sy⯑ſtem, with its inclos'd Fluid, ſteaming and reeking hot through innumerable Paſſages, changing Situation, ſometimes within, ſometimes without Doors, and expos'd to the cold, hot, dry, wet Air, and all the Variety of Changes which happen in that Element; the Changes which muſt happen to this Syſtem or Machine in theſe Circumſtances, are not the twentieth Part of what happens to Human Bodies; which, beſides the real Influence of the circumambient Air, is affected by the Changes with a dolorous or pleaſant Senſation, which it has not always in its Power to avoid or enjoy.

III. Heat and Cold are Qualities re⯑lative to our Senſes; and Cold perhaps only a Privation or leſs Degree of Heat or Motion. The Spirit of Wine in Ther⯑mometers being affected with the ſmalleſt Changes of Heat and Cold, is a proper Index of theſe Alterations, though the Degrees mark'd in the Tubes are not the exact Meaſures of the Quantity of [45] them: However, waving the Imper⯑fections of that Inſtrument, I ſhall only advertiſe the Reader, that in my Obſer⯑vations of the Degrees of the Heat of the Air, I refer to thoſe made by two Thermometers, Farenheit's, and one in⯑vented by Mr. Hales, fitted to Obſerva⯑tions upon his Subject. In Farenheit's Thermometer, at 32 Degrees, the Wa⯑ter in the Air begins to freeze, which is known by hoar Froſts; the Cold in⯑creaſing will ſink the Spirit to 5 De⯑grees; and it has been known to ſink it to 0 by Cold, in which ſcarce any Animal could live; by common artifi⯑cial Cold it can be ſunk 4 Degrees be⯑low 0; and by an uncommon Experi⯑ment has been ſunk 40 Degrees below 0. The Air is temperate at 46 De⯑grees, and by natural Heat ſeldom reaches 90; and if you by artificial Heat raiſe it 122 Degrees more, ſo as to reach 212, this is the Heat of boiling Water; ſo that 252 is the Diſtance between the greateſt artificial Cold, and the Heat of boiling Water; and 207 Degrees the Diſtance between the greateſt natural Cold common in this Climate, and the Heat of boiling Water by this Thermo⯑meter. The natural Heat of an adult Perſon is 92, and of Children 94. No [46] Animal can live long in an Air of 90, or near the natural Heat of the Bo⯑dy.

IV. Mr. Hales's Thermometer is chief⯑ly contriv'd for Experiments of Vegeta⯑tion. He begins his 0 at the firſt De⯑gree of Cold, or the freezing Point; and his laſt Degree of Heat is that in which melted Wax, ſwimming on hot Water, begins to coagulate; the Space between thoſe two Extremes he divides into 100 Degrees, juſtly reckoning that a Heat which keeps Wax fluid, is too ſtrong for Vegetation. Human Heat can expand the Spirit of Wine 1/ [...]0, when the Air is in a freezing Condition.

V. By Mr. Hales's Thermometer the Heat of animal Blood is to that of boil⯑ing Water, as 14 3/11 to 33. By the ſame Thermometer the Heat of the Skin is 54 Degrees of the 100, the Point at which Wax begins to coagulate, and is ſomewhat more than that of Water in which you can put your Hand. This Heat no Vegetable can bear, at leaſt in this Climate; tho' I remember Mr. Boyle mentions Heat in ſome Country which melts Wax, which is unſupportable by Human Bodies, and yet Vegetables ſur⯑vive it. By Hales's Thermometer, the Heat of Milk from the Cow is 55, of [47] Urine 58; that of an extreme hot Day was 88; a common Sunſhine Day at Noon, in July, 50; in the Shade 38; of a May or June Day from 17 to 30, the moſt temperate for Vegetation, and therefore the propereſt perhaps for Hu⯑man Bodies. What was moſt ſurpriſing was the Heat of 88, which exceeding 54, the natural animal Heat, Human Creatures could not have endured it long. He told me that it was extreme⯑ly hot for a while, and his Thermometer ſtood in the Sun.

VI. The Rarity of the Air makes it more ſenſible of the Changes of Heat and Cold, than any other Fluid. The ſmalleſt Increaſe of Heat expands it, and the Abatement of that contracts it im⯑mediately in all its Parts: The Heat of boiling Water, as was mentioned before, expands it ⅓. The Degrees of Expan⯑ſion of the Air are not determinable, for the greateſt Degree of Heat will not totally expel it; but by this continual Contractibility and Dilatibility, by dif⯑ferent Degrees of Heat, the Air is kept in a conſtant Motion. The different Degrees of Heat create a proportional Expanſion of Liquors, ſo as to make a ſenſible Alteration in their ſpecifick Gravity; that of rectify'd Spirit of Wine [48] about the Pole makes the Difference of 1/9 of its Bulk, and conſequently of its Price, bought by Meaſure: [...] ^* Mercury can be condens'd by Cold, ſo as to be as heavy as Gold: By Heat, the Air contain'd in animal Fluids is expanded; for Glaſs Bubbles in any Fluid, riſe and fall with the Changes of Heat, as well as by thoſe of the Gravity of the Air.

VII. A certain Degree of Heat, not ſtrong enough to dry or deſtroy animal Solids, lengthens and relaxes the Fi⯑bres; from whence proceed the Senſation of Faintiſhneſs and Debility in a hot Day; the Effect above-mentioned of Relaxation of the Fibres, and Expan⯑ſion of the Fluids by Heat, are evident to the Sight and Touch, for the out⯑ward Parts of Human Bodies ſwell and are plumper in hot Weather than in cold. There are many Experiments which demonſtrate the ſame thing, need⯑leſs to be inſerted.

VIII. Air extremely hot is capable of reducing animal Subſtances to a State of Putrefaction, and is particularly hurtful to the Lungs. Blood is cooler in the Veins than in the Arteries, and returns [49] to the right Ventricle of the Heart, where it is ſtill render'd cooler by a freſh Mixture of Chyle, which is cooler than Blood; but by the Circulation through the Lungs it is heated again to a Degree, ſo as to render it ſpu⯑mous. The Surface of the Veſicles of the Lungs is expos'd to the outward Air, which has a free Admittance to it. Refrigeration by cool Air is one, tho' not the principal Uſe of Air in Reſpi⯑ration; but when this outward Air is ma⯑ny Degrees hotter than the Subſtance of the Lungs, it muſt neceſſarily deſtroy and putrify both the Solids and Fluids: And this is found true by an Experi⯑ment; for in a Sugar-Baker's Drying-Room, where the Air was heated 146, or 54 beyond that of a Human Body, a Sparrow died in two Minutes, a Dog in 28 Minutes; but the moſt remarka⯑ble thing of all was, that the Dog void⯑ed a red Saliva, foetid and putrid. We owe this luciferous Experiment to the induſtrious Boerhaave, from which ma⯑ny important Inferences may be drawn; for why might not this putrid Saliva of the Dog be infectious? Conſequent⯑ly it is poſſible for peſtilential Diſtem⯑pers to begin from exceſſive Heats; no Human Creature can live long in [50] an Air hotter than their own Bo⯑dies.

IX. There are ſome Experiments which ſeem to indicate that Air, heated to a certain Degree beyond that of boil⯑ing Water cool'd again, and retaining all its common Properties of Gravity, Elaſticity, loſeth ſomething, ſo as to render it unfit for Reſpiration: But I am apt to believe, with the ingenious Mr. Hales, that in the Experiments which were made, the Air was infected with the poiſonous Steams of the Bo⯑dies through which it paſs'd in heat⯑ing; for the Air that paſſed through hot Glaſs did not kill Animals, as that which paſſed through Charcoal: But however, it is certain that Air heated with ſulphureous Steams of Candles or animal Bodies, loſeth ſome Part of its Elaſticity, and becomes unfit for a⯑nimal Functions, ſuch as the Air in which People of Faſhion paſs a great deal of their time; but of this more af⯑terwards.

X. Another great Effect of the Heat of the Air upon Human Bodies is, that by the Degrees of it the Quantity of Perſpiration, ſenſible and inſenſible, is regulated. By Journals that have been kept it appears, that the Perſpiration of [51] England ſcarcely equals all the other Excretions, and that the Summer Per⯑ſpiration is near double to that of Win⯑ter; whereas in Paduan Air, the Per⯑ſpiration the Year round is to all the o⯑ther Excretions as 5 to 3, and perhaps in hotter Countries the Proportion is greater. This muſt occaſion a great Variety of Human Conſtitutions and Diſeaſes, according to different Climates. The ſerous Part of the Blood being carried off by Sweat or ſenſible Perſpi⯑ration, which is much greater in hot Countries than in cold or temperate, muſt make the Craffamentum or red Cake of the Blood more; and a Phyſi⯑cian who has practis'd in thoſe Coun⯑tries, has aſſur'd me that the Caſe is ſo, that the Blood is commonly black and denſe when drawn. I have often been ſurpris'd that the Quantities of Spices, which the Inhabitants of hot Countries take, do not hurt them; but on the other hand I conſider, that Nature is wiſe, and had not made thoſe Plants in⯑digenous, unleſs they were uſeful and neceſſary, perhaps for attenuating the Blood depriv'd of its Fluidity by the great Quantity of ſenſible Perſpiration; and to recruit it with the volatile and oily Parts of which it is depriv'd, [52] both by ſenſible and inſenſible Perſpira⯑tion.

XI. I would likewiſe obſerve, That the real Quantity of animal Pluid car⯑ried off by Perſpiration, can never be known by Ponderation; for as it is plain that the outward Air enters the Pores of the Body, and is ſometimes imbib'd or abſorb'd by the Animal, the Quan⯑tity of perſpirable Matter is only the Difference of the Exceſs of that be⯑yond the Quantity of Air that is imbib'd; of this more in the following Part of this Chapter.

XII. Winds do not cool the Air by their Motion, but by bringing along with them the Air of cooler Regions. The Thermometer does not change by Winds, nor by the ſtrongeſt Blaſt of a Bellows, unleſs it be blown through Ice, or any Body colder than the Air, and ſuch a Blaſt will ſink it. The rapid Motion of great Storms rather agitates and heats the Air; but Winds cool ani⯑mal Bodies by driving away the hot Steam that ſurrounds them: Suppoſe the Heat of an animal Body to be 90, and the Heat of the Air 48, the animal Body by blowing off the hot Steam will be ſurrounded with an Atmoſphere of 48, near the Half of its natural Heat, [53] taken off in a Second of Time; there⯑fore reſting in a cool Air after Exer⯑ciſe may be the Cauſe of great Diſeaſes, eſpecially ſuch as affect the Lungs, In⯑flammations, Aſthmas, Catarrhs; this Change of their Atmoſphere happening, as was ſaid, every Second of Time, is the ſame thing as putting on a cold Suit of Clothes every ſuch time.

XIII. On the other hand, as Human Bodies can be cool'd by Air cooler than their own Temperature, perhaps ſooner than by any other Means, there is great Uſe to be made of temperating feveriſh Heat by outward Air, ſo that it be done with Safety; this is known by Experience in inflammatory Diſtempers, as in the Small-pox. No Liquor taken inwardly can cool Human Blood ſo ſoon as cool Air. Boiling Water is reduc'd to its own Temperature in a ſhort time, by cool Air. Two Liquors of equal Denſity, and unequal Degrees of Heat, being mix'd in equal Quantities, re⯑duce the Heat of the Whole imme⯑diately to half the Sum; for Example, boiling Water hot as 212 Pound, to an equal Quantity of Water cold, as 32, makes the Heat of the whole (212+32)/2=114. A Liquor of leſs Denſity, ſuch as Air, [54] is indeed longer in producing this Ef⯑fect; and Air cools the Blood by its Contact or Admiſſion into the Surface of the Skin, or the Lungs. Innumera⯑ble Miſchiefs ariſe from keeping the Air of the Room of a feveriſh Perſon too hot, by depriving the Patient of the Benefit of Refrigeration by cool Air; from the bad Effects of animal Steams, which ſpoil the Air, and de⯑ſtroy its Elaſticity, as will appear by what is ſaid afterwards, it is known by Experience that Patients in Fevers affect cool Air, and will uſe their utmoſt Ef⯑forts to come at it, even by getting out of Bed. I am of Opinion that renew⯑ing and cooling the Air in a Patient's Room, giving it a free Admiſſion by o⯑pening the Door, the Bed-Curtains, and in ſome Caſes the Windows, or letting it in by Pipes, changing the hot At⯑moſphere about him, ſo as not to diſ⯑appoint the Intention of keeping up a due Quantity of Perſpiration; and in ge⯑neral, the right Management of the Air is one of the chief Branches of a Re⯑gimen in inflammatory Diſtempers; and by the ſcrupulous Care of ſilly Nurſes in this Particular, the Diſeaſe is often increas'd, lengthen'd, and proves fatal; and this Error is ſtill more dangerous [55] in vigorous, ſtrict, and ponderous Bo⯑dies, than in lax; for Heat is detain'd in Proportion to the Denſity of Bo⯑dies.

XIV. The Effects of cold Air may be inferr'd from what has been ſaid of hot Air; Cold being a Privation or A⯑batement of ſo many Degrees of Heat, induceth a proportional Diminution of the Effects of Heat or contrary Quali⯑ties. Cold Air is the immediate Cauſe of Freezing; it firſt begins in the Air by Congelation of the watery Particles in it; and the Effects of this Cold ſome⯑times do not reach ſo far as the Sur⯑face of the Earth, ſo as to freeze the Water on it; as in Summer Hail, and Icy Showers, ſuch as that which fell in Somerſetſhire and Oxfordſhire in 1672: ſo deſtructive of Vegetables, ^* the Sur⯑face of the Earth was not frozen. In Farenheit's Thermometer Freezing be⯑gins at 32, and increaſing, will ſink the Spirit of Wine to o, which is a De⯑gree ſcarcely ſupportable by animal Bo⯑dies: Artificial Freezing will ſink it below that Point. Vegetables endure greater Degrees of Cold than Animals, [56] and yet great Deſtruction is made of them by Winter's Cold ſometimes, as that of 1684, and in ſome Countries 1708; becauſe Human Creatures have Defences againſt the Injuries of the Air.

XV. Cold condenſeth the Air pro⯑portional to the Degrees of it; it con⯑tracts animal Fibres and Fluids, which are denſer as far as the Cold reacheth. In cold Weather Animals are really of leſs Dimenſions. Cold braceth the Fi⯑bres not only by its condenſing Quality, but likewiſe by congealing the Moiſture of the Air, which relaxeth. Extreme Cold works on Human Bodies as a Sti⯑mulus, producing at firſt a pricking Sen⯑ſation, and afterwards a glowing Heat, or a ſmall Degree of an Inflammation in the Parts of the Body which are ex⯑poſed to it. By bracing of the Fibres more ſtrongly, condenſing the Fluids, and ſtimulating, it produceth Strength and Activity, which is very ſenſible to ſome in clear froſty Weather. If the Effects of cold Air are ſo conſiderable upon the outward Surface of the Body, they may be much more ſo upon the Loogs, in which the Blood is much hotter, and the Coat very thin, in im⯑mediate Contact with the outward Air; [57] and were it not that the warm Air is not intirely expell'd in Expiration, the Contact of the cold Air would be in⯑tolerable; and indeed the Effect of cold Air in producing Inflammations of the Lungs is very ſenſible, eſpecially upon the blowing of cold North-weſterly Winds in ſome of our Northern Planta⯑tions in the Weſt-Indies. Cold condenſeth all Fluids, except Water, which it ra⯑rifies to 1/9 of more Bulk; Ice emergeth ſo much out of Water: As Froſt ſe⯑parates Air from Water, and collects it into Bubbles, it may be ſuſpected that the ſmall ſpecifick Gravity of Ice is not owing to inviſible Maſſes of Air in the Ice; for Air ſeparated from any Liquor takes up a greater Space than in the Liquor, and conſequently renders the ſame Aggregate of Air, and Water ſpe⯑cifically lighter. Perhaps this may ſolve the Difficulties Mr. Boyle had about this Matter. Freezing Cold contracts all o⯑ther Liquors beſides Water, as oleagi⯑nous Liquors and Spirits, as to make them ſpecifically heavier; Air, it will condenſe 1/10.

XVI. Cold, by contracting the Fibres of the Skin, and cooling the Blood too much in thoſe Veſſels which are ex⯑poſed to the Air, ſuppreſſeth ſome of [58] the groſſer Parts of the perſpirable Mat⯑ter, by which many Salts which would evaporate in warm Air are retain'd; and likewiſe by a Stimulus the cold Air vel⯑licates and inflames theſe Veſſels, pro⯑ducing Scurvies, with the moſt diſmal Symptoms: Scurvy is the Diſeaſe of cold Countries; the fatal Extremities of it one may ſee in the Journals of ſuch as have been left to winter in Greenland and other cold Countries; the Cold that froze their ſpirituous Li⯑quors had nearly the ſame Effect upon the Blood, reducing to a gangrenous State the animal Subſtances, Mortifications of their Limbs, Gums, the putrid Fleſh being forc'd to be cut off, a total Inability of Chewing, Immobility, and intolerable Pains in many Parts of the Body, livid Spots and Bliſters on their Skins; and, by regarding the Motion of the Blood, and Suppreſſion of Perſpiration, Giddineſs, Sleepineſs, Pains in the Bowels, Looſe⯑neſs, Bloody-fluxes; but what is very ſtrange, ſeldom a Decay of Appetite; Theſe were not intirely the Effect of Salt Proviſions; beſides, they had often freſh, both vegetable and animal; if living in ſuch cold Countries be prac⯑ticable, it muſt be ſo far under-ground as reacheth beyond the Froſt, which [59] feldom pierceth above the Depth of 10 Feet. The Air in the Grotto of the Obſervatory of Paris, of 130 Foot deep, is equable and temperate: There is a certain Diſtance at which the na⯑tural Heat of the Earth is not deſtroy'd by the outward Air. Froſt in ſuch a Degree as does not congeal animal Flu⯑ids, may increaſe inſenſible Perſpiration. Liquors loſe their volatile Parts in froſty Weather more than in hot, by con⯑denſing the watery Parts, the Volatile fly off. Scents are not abared by Cold^*, but, as I ſaid before, ſome of the groſ⯑ſer Salts are retain'd in Perſpiration.

XVII. Extreme Cold and extreme Heat deſtroy or reduce to a gangrenous State animal Subſtances, with this Dif⯑ference, that the Cold which produceth Mortifications in living Bodies, preſerves the Dead from Putrefaction; for there muſt be a Concurrence of Heat and Motion in the animal Juices with the Stimulus of the Cold, to produce the Change; we cannot raiſe a Bliſter on a dead Body.

XVIII. The Interchanges of Heat and Cold, and the conſtant oſcillatory Mo⯑tions of Contraction and Dilatation pro⯑duc'd [60] by them, are neceſſary for the Oeconomy of Animals and Vegetables, but neither can bear the Extremities of them. In all Probability the ſame De⯑gree of Heat has perſiſted about the Earth ever ſince the Creation; the Cauſes which produce it are the ſame. Ani⯑mals and Vegetables have been produc'd, and continued to grow after the ſame manner, which is a Sign that the Heat has wrought after an uniform manner, and that the Quantity of it upon the Surface of the Earth has continued the ſame; it may be increas'd in particular Places, but when the Pabulum which produc'd it is conſum'd, there is no more Heat communicated to the reſt of the Matter. There does not ſeem to be any natural Cauſe for the Increaſe of Heat on the Body of the Earth, unleſs it be the Approach of a Comet. The Spots that appear and diſappear on the Surface of the Sun, can make no great Altera⯑tion.

XIX. As to the Degrees of Heat, a Heat of 90, by Farenheit's Thermometer, turns the White of an Egg liquid, ſanious, and putrid; a Heat of 200 will harden it. Vegetable Heat, in which Plants will live or grow, is from 1 to 80; a⯑nimal Heat, terreſtrial, from 40 to 94; [61] of Fiſhes that have Gills 34, and which can bear Heat to 60; but Fiſhes which have Lungs can bear Heat from 34 to 94. Water begins to grow hot at 94, and boils at 212. 600 is a melting Heat. A catoptrical or dioptrical Heat is ſupe⯑rior to any, vitrifying the hardeſt Sub⯑ſtances.

XX. The Effects of Moiſture on the Air, both on Animals and Vegetables, are Relaxation of their Fibres; by ma⯑ny Experiments I have found that the ſingle Fibres, both of Vegetables and Ani⯑mals, are lengthened by Water or by moiſt Air; a Fiddle-ſtring moiſten'd with Water will ſink a Note in a little time, and conſequently muſt be relaxed or lengthened 1/16; the Steam of hot Wa⯑ter will ſink it a Note in 5 or 6 Mi⯑nutes. That Moiſture relaxeth is evi⯑dent by daily Experience, of Paper, Vel⯑lum, a Drum, Leather. Vegetable or animal Fibres firſt moiſten'd, and after⯑wards dry'd, contract more than before they were moiſten'd. It muſt happen indeed that Water, inſinuated into the Pores of any Body, increaſeth its Dimen⯑ſions; and perhaps by this Mechaniſm it ſhortens Ropes, by increaſing their Thickneſs. A cold Bath makes a mo⯑mentary Contraction of the Fibres by [62] the Cold, and the Senſation of which in live Bodies works as a Stimulus; but the Water itſelf would relax, and con⯑ſtantly does ſo, when its Degree of Heat is equal to that of our Bodies, and con⯑tinuing long in cool Water, at laſt re⯑laxeth. Swimming long diſpirits more by the Relaxation of the Water, than Exerciſe. Water and Air produce Vo⯑latility or Putrefaction in Bodies, and ſtill in a greater Degree if aſſiſted by Heat. Moiſture helps Air to inſinuate itſelf into the Pores of Bodies. A Blad⯑der will ſooner burſt than let Air paſs when dry, but when moiſten'd lets it ea⯑ſily paſs. Moiſture diminiſheth the Ela⯑ſticity of the Air; in rainy Weather the Air is leſs elaſtick. Thus Moiſture re⯑laxeth Human Fibres, by weakening the Spring of the Air. Dry Air either abates thoſe Effects, or produceth their Con⯑traries. Dry Air ſucks up the volatile Oils of animal Bodies, by which means it influenceth Perſpiration. Freezing Cold ſeparates Air from Water; for as the Water freezeth, the Air appears in Bub⯑bles, which are ſometimes inclos'd in Ice.

XXI. To the Relaxation of the Fibres by moiſt Air, are owing a great many Symptoms which Human Bodies feel in [63] moiſt Weather (by which Relaxation they loſe ſome of their Elaſticity or Force for circulating the Fluids) eſpe⯑cially thoſe Aches and Pains which they feel in thoſe Parts where the Circulation of the Juices is not perfect, as in Cica⯑trices of Wounds, luxated or bruiſed Parts. I wiſh I could thoroughly un⯑derſtand the Cauſe of a Corn's aching before Rain, from which I ſhould be able to explain the Cauſes of all thoſe Pains which affect ſome Bodies in wet Weather.

XXII. Moiſt Air is properly that which is overcharg'd with Vapours near the Sur⯑face of the Earth; and when thoſe Va⯑pours are rather in a falling than an aſ⯑cending State, the Body of Air may contain more Water in it at other times; but, as was ſaid before, the Water and Air are better mix'd, the Vapours are higher, and a leſs Quantity of them in Contact with our Bodies; we call Air in ſuch a State, dry; the Air may be ſaid to be ſometimes in a State of imbibing, and ſometimes in a State of precipitating its Water.

XXIII. The Effects of dry Air are contrary to theſe of moiſt, becauſe they are an Abatement or Privation of them. Dry Air imbibes volatile animal Oils and [64] Spirits, and conſequently influences Per⯑ſpiration. Great Dryneſs may change the very Texture and Situation of the Pores of the Skin. Of the two, extreme dry Seaſons have proved more dan⯑gerous to Human Bodies than wet. Our Bodies are not made to bear Ex⯑tremities of any kind, but extreme Droughts have been found moſt dan⯑gerous to Human Bodies. All theſe fore⯑mention'd Properties and Qualities of the Air, Gravity, Elaſticity, Heat, Cold, Moiſture, Dryneſs, act in their ſeveral Combinations on Human Bodies; and when their Actions conſpire, the Effect produced is the Sum; when contrati⯑wiſe, the Effect is the Difference of their Actions.

XXIV. Air, by the Properties and Qualities enumerated, muſt produce ve⯑ry ſenſible Changes in Human Bodies, becauſe it not only operates by outward Contact, but we conſtantly imbibe it at all the Pores of the Body, which is evi⯑dent by what has been ſaid before; for if the Air had not a conſtant Admittance into the Body, how could the Balance of the external Air, and that within the Veſſels, be ſo quickly reſtor'd; upon this the Life of the Animal depends, to balance the Air within and without the Body; [65] it requires indeed ſome time in deſcending in the Diving-Bell: there is one trouble⯑ſom Senſation, and it is a ſtrong Preſ⯑ſure upon the Membrane of the Ear, where it has not ſo ready an Admittance; but changing the Denſity of the Air not too faſt, by the free Communication of the denſer outward Air and that of the Body, there is no Danger nor uneaſy Senſation. The Skin of an Animal dry'd, or Leather, excludes Air; but the Skins of live Animals are moiſt and oily, through which Air will paſs. Where⯑ever there are Emiſſaries, there are like⯑wiſe abſorbing Veſſels. Many Bodies denſer than Air, as Mercury, Cantha⯑rides, Garlick, enter the Pores of the Skin. While we perſpire, we abſorb the outward Air, and the Quantity of per⯑ſpired Matter found by Ponderation, is only the Difference between that and the Air imbib'd; ſo that after great Labour and Abſtinence, which produces a Va⯑cuity, and a great Diminution of Per⯑ſpiration, it is poſſible that the Quanti⯑ty of the Air abſorb'd may exceed the perſpired Matter: This is true, if the Journals of Perſpiration be faithful. In Dr. Keil's Journal there is an Inſtance of a Perſon growing 18 Ounces more ponderous by abſorbing Air. The Peo⯑ple [66] of Newmarket, who try the Methods of Waſting, aſſirm this to be true; tho' I own I ſhould be very glad to have it confirm'd by ſome faithful Trial. Hippo⯑crates and Galen took the Doctrine of abſorbing of Air for granted, and reaſon from it. This Quality of generating Air, and abſorbing it at different times, has been demonſtrated by the ingenious Mr. Hales in many Bodies, eſpecially in Vegetables, by plain Experiments; by which it appears that Air enters freely through the Bark, Steam, and Leaves, and all the outward Surface of Vege⯑tables, which are ſometimes not in a State of Perſpiring, but in a State of imbibing Air, as in the Night. Another very re⯑markable thing is, that Air paſſeth eaſier through the Barks of old Trees than of young. Q. If by Dryneſs, Shrinking, and Hardening, the Pores of the Skins of old People may not grow wider? They are indeed more coreacous, but Air paſſeth through dry Membranes when moiſten'd. By an Experiment of the in⯑genious Profeſſor Myſſchenberg, it appears that Air tranſmitted through clavellated Aſhes into an exhauſted Receiver, loſes Weight as it paſſes through them, and more or leſs, according to the Degree of Moiſture in the Air. Volatile Salts, ſuch [67] as thoſe of Animals, do not generate, but abſorb Air; and it is very probable that Human Bodies abſorb the Water from the moiſt Air, as fixt, dry, alka⯑line Salts do; which will explain a great many Symptoms ariſing from cold and moiſt Air. Many great Effects muſt follow, and many ſudden Changes may happen in Human Bodies, by ab⯑ſorbing outward Air with all its Qua⯑lities and Contents; nothing accounts more clearly for epidemical Diſeaſes ſeizing Human Creatures inhabiting the ſame Tract of Earth, who have nothing in common that affects them, except Air; ſuch as that epidemical Catarrhous Fever of 1728, and of this preſent Year; it could not proceed merely from the Sup⯑preſſion of Perſpiration by Cold, the Weather having been felt colder at other times; beſides, it is known by Expe⯑rience, that the mere Suppreſſion of Per⯑ſpiration does not always produce a Ca⯑tarrh, nor that keeping it up prevents one; it ſeems rather to be occaſion'd by Effluvia, uncommon either in Quantity or Quality, infecting the Air.

CHAP IV. Of the Nature of Air in different Situa⯑tions, Regions, and Seaſons.

I. AFTER having ſaid ſomething of the Contents, Properties, and Qualities of Air in general, and their Effects; it behoves us to take notice of its local and temporary Qualities, which may be deduc'd not only by Conjecture, but demonſtrative Reaſon, from what has been ſaid before. As to the Con⯑tents of Air, it is evident that they muſt differ according to the Nature of the ſurface of the Earth or Water from which they exhale; and this Difference would be permanent in every Spot of the Surface of the terraqueous Globe, did not the whole Maſs of Air com⯑municate as a Fluid, and were not its Parts agitated and mix'd together by the Motion of Winds and other Methods of the wiſe Author of Nature: Yet the Mixture is not ſo perfect but it leaves ſome Difference in the Nature of the Air, ſenſible to the Inhabitants of the ſame Tract of Ground where the Exhalations are conſtant, and conſtantly mix'd with the Air. Dew is the Exha⯑lation [69] of the Earth, return'd again, and precipitated upon it; conſequently the Nature and Contents of the Dew of any Place, ſeem to be the beſt Mark of the Exhalations of the Soil of that Place. Dew, by Chymical Trials, yields different Contents, according to Places, as the Soil is watery, ſalt, unctuous, ſa⯑line, mineral; and differs according to the Quantity of Heat by which it is rais'd, either from the Sun, or inward from the Earth. The local Qualities of the Air are more permanent in Calms, than in Winds: This is evident from Fogs, which are the Conſequence of Calms; therefore the Air retains its lo⯑cal Qualities long in Mines, Grottos, Ditches, not perflated; and in Valleys longer than on the Tops of Moun⯑tains.

II. The Exhalations from great Sur⯑faces of Water, as the Sea, are ſcarce⯑ly any thing but Water, the Sun nei⯑ther acting upon the bottom, nor ex⯑haling the Salt. Winds raiſe ſome of the Salt with the Spray, as has been known by Experience in great Storms; the Bars of Windows, and Iron, ex⯑pos'd to the Sea Air, are apt to ruſt; this Salt is not unfriendly to Human Conſtitutions, but the great Maſs of Ex⯑halation [70] is freſh Water; and were it not for conſtant Winds which blow off the Coat of Vapours which inveſts the Sea, I am of opinion that Sea Air would be intolerable to Human Bodies.

III. The Contents of the Air muſt differ much in Froſt, and open Weather: Great Froſts ſtop the Perſpiration of the Earth, and conſequently deprive the Air of the Ingredients of thoſe Exhalations; accordingly, it has been found by Ex⯑perience, that when there are noxious Exhalations in the Air, the Caſe perhaps of peſtilential Seaſons, that they have been ſtopt by Froſt: Froſt congeals and ſeparates the Water from Air. On the other hand, in Thaws, the Perſpiration of the Earth being reſtor'd, and its Ex⯑halations more copious, frequently ren⯑der ſuch Seaſons unhealthy; ſuch was the Conſtitution preceeding the laſt Plague of London, a hard Winter, ſudden Thaw, a great Quantity of Water upon the Ground, attended with Heat; ſuch an Air could not miſs to produce great Sickneſs, wherein Mankind liv'd as it were in a wet Cellar, with a great Fire. Summer Air differs conſiderably from that of Winter, from the Air's being re⯑plete with the perſpirable Matter of Ve⯑getables. Rains, after great Droughts, [71] muſt, in ſome meaſure, produce the ſame Effect as Thaws after great Froſts. The Air of Cities differs from Country Air, for many Reaſons. See Numb. VIII. XI. Chap. I.

IV. The Contents of the Air of any Place differ according to its Situation, in reſpect of adjacent Places, from whence the Air is brought by Winds: A high Ground, dry, and naturally healthy, bor⯑dering upon low marſhy Ground, muſt neceſſarily be ſickly, when the Winds blow over thoſe Marſhes; beſides, high Grounds attract Vapours as they riſe from low Grounds. In chooſing Situations, not only the Nature of the Soil on which you build, but the Nature of the neigh⯑bouring Grounds and Soil is to be conſi⯑dered.

V. A rich fertile Soil, abounding with Variety of active, volatile, and unctuous Particles, with a conſiderable Degree of Heat, muſt neceſſarily produce inflamma⯑tory Diſtempers in Human Bodies; ſuch are rich Meadow Grounds, upon the Banks of Rivers, which, with the in⯑creaſing Heat of the Spring, bring Fe⯑vers, eſpecially intermitting: Such rich Grounds, in very hot Climates, are ex⯑tremely unhealthy, as we find by the Re⯑lations of Travellers. On the other hand, [72] a gravelly Soil, on the Banks of a run⯑ning Stream, is generally healthy.

VI. Mountainous Places abound with watery Vapours. Hills attract Vapours; Woods attract Vapours, and ſtop the Per⯑flation by Winds; yet chalky and gravel⯑ly high Grounds which have no unwhol⯑ſom Perſpiration, nor are in the neigh⯑bourhood of marſhy and low Grounds, are generally healthy.

VII. Both the ſuperficial Effluvia of the Earth, and thoſe of Minerals, which lie lower, affect the Air, as is known by Experience: People who paſs over Ground abounding with Mines are ſenſi⯑ble of offenſive Steams. The Averni in Hungary kill Animals, and alſo Birds that fly over them. Mr. Boyle is of Opi⯑nion that more Places abound with Mi⯑nerals, eſpecially Marcaſites, than are ſuſpected. Minerals muſt needs affect the Air, when they enter the very Subſtance of Plants, of which there are very few that have not Iron in them. The aſcending Fumes from the Mines in Devonſhire, have blaſted all the Vegeta⯑bles, as Graſs, Fern, &c. All mineral Steams are not unwholſom; Mr. Boyle gives Inſtances of ſome that emic a ſweet and refreſhing Savour, as in a Mine in Hungary, affording an Ore call'd [73] Rot Gulden erts, the Steam of which is ſo refreſhing, that People chooſe to en⯑joy it in taking the Air. The Tinners are not more unhealthy, nor ſhorter liv'd, than other People. Limeſtone is reckon'd wholſom; it is warm, and quickly diſ⯑ſolves Snow, and cauſes excellent and wholſom Graſs. Mr. Boyle, from a white Earth, extracted a rich volatile Spirit. There are Methods to diſcover what Sorts of Steams are in the Air, which it may be of Importance ſometimes to try.

VIII. The Methods which Mr. Boyle adviſeth for diſcovering what Salts are in the Air, are, to expoſe ſuch Bodies as are affected with thoſe Salts; as dy'd Silks of particular Colours, which will be tar⯑niſh'd with nitrous Salts: Preparations of Sulphur are blacken'd with vitriolick Salts; to try what Alterations are made upon white Linen, freed from Sope and Lye, by Steams or Dews; Experiments of Bodies diſcoloured, or otherwiſe af⯑fected by different Spirits; Spirit of Ni⯑tre makes with Copper, a paliſh Blue; Spirit of Salt, a Green; Spirit of Urine, a deep Blue. In ſome Places, as in Am⯑ſterdam, Plate tarniſhes ſoon. The Cop⯑per-Mines in Sweden affect the Silver that is near them, and make it black. In [74] ſome Places Furniture rots, Metals ruſt. But I think there is no better way of judging of the Air of any Place, than by the Water which muſt neceſſarily im⯑bibe the Salts, Sulphurs, and other Mi⯑nerals, through which it flows; and when it is free from any Savour from thoſe Subſtances, it is probable the Ground is ſo too. Sulphurous Steams, ariſing by ſubterraneous Heats, whiten the Waters of Springs, and are certain Pro⯑gnoſticks of an Earthquake; and I think it may be concluded, that where the Water is good, the Air is ſo likewiſe. Sulphur in the Air may be diſcover'd by Smell, as is perceiv'd in Vulcanos and Storms. Sulphureous Airs may be fir'd with a Candle.

IX. Moiſture in the Air is diſcover'd by Hygroſcopes: And an Air naturally moiſt diſcovers it ſelf by its Effects upon Furniture, Plate, and ſeveral other Bo⯑dies; and is ſometimes to that Degree in Thaws after great Froſts, as to wet the Stair-caſe, Wainſcot, Pictures, and other Furniture.

X. As to the Gravity and Elaſticity of the Air, they decreaſe with the Height, as was mention'd Chap. II. and it ſeems almoſt incredible, that a Human Crea⯑ture can live at the bottom of a Mine, [75] with the Mercury at 32 Inches high; and at the Top of a Mountain of three Miles, perpendicular Height, where the Mercury ſtands at 16, that is, with the Weight of the Atmoſphere; in the firſt Caſe at 32000 Pounds, and in the ſecond at 16000; perhaps there are ſcarcely any Human Creatures who reſide conſtantly in thoſe Extremes; if there were ſuch, there muſt be a great Diverſity of Con⯑ſtitutions and Diſeaſes; but a ſmaller Difference in the Weight of the Air, muſt create a great Diverſity of the Ef⯑fects of the Air, on the Inhabitants of thoſe different Regions.

XI. The Changes of the Gravity of the Air, affecting Human Bodies with oſcillatory Motions of the Solids and Flu⯑ids, the more frequent and great thoſe Changes are, the greater Effects they will have upon the Nerves and Spirits; but ſo it is, that within the Tropicks, where there are no variable Winds, the Variations of the Height of the Mercu⯑ry are but ſmall; from whence there muſt ariſe a Diverſity of Tempers and Conſtitutions between the Inhabitants of ſmall and great Latitudes, upon account of the greater Variableneſs of the Gravity of the Air: Of theſe Particulars we ſhall ſay more afterwards

[76] XII. The Air, by Elaſticity, concur⯑ring with its Gravity, inſinuates itſelf into animal Bodies. There are Sub⯑ſtances, which, mix'd with Air, abate and deſtroy ſome of its Elaſticity, eſpe⯑cially ſulphureous Steams, as thoſe of Candles, Animals, which render the Air unfit for Reſpiration. The Air in which ſuch Steams reſide, is very different from pure Air.

XIII. Heat, as far as it depends upon the Action of the Sun, is menſurable in different Climates. The Quantities of it have been geometrically determin'd by Dr. Halley ^*: For Example, the Equi⯑noctial Heat under the Line, is to the Equinoctial Heat in 60 Degrees of Lati⯑tude, as 2 to 1; to that of the Latitude of 50, ſomewhat leſs than 10 to 6. The Tropical Heat under the Line is leſs than in a Latitude of 50, nearly in the Propor⯑tion of 9 to 11. The Tropical Heat under the Line is the leaſt of any Situa⯑tion upon the Globe. The Tropical Heat under the Pole is greater than that un⯑der the Line, in the Proportion of 5 to 4; the Duration of the Sun above the Horizon, the whole 24 Hours, over⯑balancing the Difference of the Inclina⯑tions [77] of its Rays. In all appearance, if there was no Sun, the Fluids above the Surface of the Earth, or within a cer⯑tain Depth of it, would be abſolutely rigid and frozen, ſo that there would be no Fluid at all; perhaps the Air it ſelf, without the Action of the Sun, would not continue fluid. The Fluids are ſo much frozen in great Latitudes, by the Abſence of the Sun, that the Quantity of Heat is not ſufficient, du⯑ring its Stay, to melt them and warm the Atmoſphere, which is kept cold by the Ice on the Surface of the Earth. Heat and Cold are retain'd longer in Bodies, in Proportion to their Denſities.

XIV. There is a Cruſt of ſolid Ice round the Pole, perhaps for ſome De⯑grees, which, by a hard and cold Win⯑ter, may get more Ground than it loſeth in the ſucceeding Summer, and, being carried by Winds, affects the Air of leſſer Latitudes with great Coldneſs. The Neighbourhood of great Bodies of Ice, produce in great Tracts of Land greater and more laſting Degrees of Cold than are proportional to their La⯑titudes, and which never ceaſe till that Ice is melted. The Cold in the Paral⯑lel of London is much greater in the Weſt-Indies. The midland Countries of [78] great Continents are colder than thoſe that have the Sea Air. Moſcow, in the ſame Latitude with Edinburgh, is much colder.

XV. The ſame Southern Latitudes are colder than the Northern, from an Aſtronomical Cauſe, which, if the Rea⯑der does not underſtand, he may take it in this Light: The Time from the Ver⯑nal Equinox to the Autumnal, is 9 Days more than from the Autumnal to the Vernal; conſequently the Summer in our Hemiſphere is 9 Days longer than that of Southern Latitudes, which Cauſe, working a vaſt Number of Years, muſt heat our Hemiſphere more than the Southern. Dr. Halley met with a Sea unnavigable for Ice, in the Latitude of 51, in the Month of January, which is the ſame thing as Ice in our Seas in the Month of July.

XVI. It is plain, that the Degrees of Heat in ſeveral Places of the Earth, bear no regular Proportion to the Action of the Sun, which is uniform. The great Diverſity of Seaſons in the ſame Place, may perhaps depend, in ſome meaſure, upon ſome Action of the Sun upon the Earth, reſembling the Opera⯑tions of Chymiſtry, raiſing ſome ſubter⯑raneous Steams of different Qualities [79] and Quantities, at different times. In the Year, 775. it is reported by an ^*Hi⯑ſtorian, that the Mediterranean was fro⯑zen along the Coaſt to the Diſtance of 50 Leagues.

XVII. The Heat of the Air depends, in ſome meaſure, upon the Conſtitution and Temper of the Surface of the Earth, which in ſome Places retains Heat more than in others. Black Earth imbibes the Sun's Rays: Expoſe a black and a white marble Ball to the Sun Beams, in a clear hot Day, the white will be perfectly cool, while the black acquires a Heat that would roſt an Egg. Sandy Ground, by reflecting the Sun-beams e⯑very way, heats the Air, is offenſive to the Eyes; and, by the Heat of the Sand in ſome Countries, inſufferable to the Feet. The Heat of the Iſland of Or⯑mus, which lies beyond the Tropick of Cancer, is ſo intolerable at ſome time of the Day, by the Reflexion of the Sun-beams from the white Mountains of Salt, that the Inhabitants are forc'd to im⯑merge themſelves in Water.

XVIII. Hot Steams riſing from the Surface of the Earth, heat the contigu⯑ous Air. The Heat of particular Days [80] depends ſometimes upon the Reflexion and Refraction of Sun-beams from Clouds, by the Laws of Catoptricks and Dioptricks. The greateſt Degree of Heat is producible by Attrition. The Parts abraded by the Attrition of Flint and Steel, are Glaſs, which is the utmoſt Effect of the Heat of a Burning-glaſs, and more quick: And it is poſſible that the greateſt Degrees of Heat in the Air, as Storms and Thunder, may be produc'd by the Colliſion and Fall of Icy Bodies in the Air.

XIX. The Heat decreaſeth with the Attitudes from the Surface of the Earth, it being leſs on the Tops of Mountains than in Valleys, becauſe the Air being a Fluid extremely rare, retains Heat but a ſhort time. The Incidence of the Rays of the Sun, does not create any laſting Heat in the Air. The Air, at a ſmall Diſtance from the Focus of a Burning-glaſs, which vitrifies Metal, is not hotter than other Air. The Heat excited in the Air by the Rays of the Sun is immediately extinguiſh'd by intercepting them. In a Green-houſe, the Parts not touch'd by the reflected Rays of the Sun, grow rather cooler than outward Air. Denſe Bodies retain Heat, excited by Sun-beams a longer time, in Proportion to their [81] Denſity, the Air not the ſmalleſt Inſtant, as on the Tops of Mountains, where it is de⯑priv'd of the Heat and Reflexion from the Surface of the Earth. In the middle of the Torrid Zone, in the Iſland of Ceylon, as you aſcend the Air grows ſtill cooler. The Tops of Mountains, in very hot Countries, are cover'd with Snow. ^* As you aſcend from the Red-Sea in Aethio⯑pia, the Air grows ſtill more temperate, till on the Tops of Mountains it grows more unſufferable than the Heat in the Valleys. It is by hot Air, and not by the Action of the Sun, that Ice melts. The Heat of the Sun, in a clear froſty Day, has but a ſmall Effect upon a Surface of Ice. Joſeph d'Acoſta tells us, that the Air in one very high Mountain of Peru is mortal, at the firſt Blaſt, and by its Coldneſs preſerves the dead Bodies from Putrefaction. He tells us, that on the Top of the Mountain of Peru, per⯑haps the higheſt in the World, he and his Company were ſeiz'd with bilious Vomitings, perhaps from the Thinneſs, as well as Coldneſs of the Air.

XX. As the Air in higher Regions is colder, ſo it ſeems to begin there, and de⯑ſcend towards the Surface of the Earth; it [82] affects the Water at the Top firſt, which, in extreme Froſts, will freeze to the Depth of 3 Inches in 24 Hours. The Suppoſition of Froſt being produc'd by nitrous Particles in the Air, is not well ſupported; the Steams of Nitre have no greater Effects than thoſe of other ſaline Liquors in producing Cold. Spi⯑rit of Nitre diſſolves Ice. In general, the Suppoſition contradicts Experiments, where Nitre rather diſſolves Ice than pro⯑duceth it.

XXI. Mere Freezing is not the Mea⯑ſure of Cold, for it begins to freeze at 32; but the Cold may increaſe till it brings the rectify'd Spirit to o, a Cold inſufferable by Human Bodies, and in which the moſt ſpirituous Liquors freeze: The ſtrongeſt Motion, and the greateſt artificial Heat by Fires, can hardly preſerve Human Bodies from freezing. The natural Heat of a Human Body is 90, and it can ſubſiſt in Degrees of Heat between leſs than 90, and ſomewhat a⯑bove [...] As the Difference of the Gra⯑vity of the Air, which Human Bodies can ſuſtain, is ſurpriſing; no leſs ſo are the Limits of Heat and Cold ſufferable, by the help of Art and Cuſtom; in Cold to o, in the Thermometer; and in Heat beyond the Limits of 90 Degrees [83] mentioned. There are ſome Countries, as in Suagena, in which Wax is melt⯑ed tho' lock'd up in Cabinets; where Bodies in Summer are excoriated by Heat, as in Northern by Cold; Shoes are burnt as it were with a hot Iron: But Human Creatures muſt have ſome Means of defending themſelves from thoſe exceſſive Heats, elſe they could not live.

XXII. As the Heat decreaſeth from the Surface of the Earth upwards, the Effects of Froſt ſcarcely reach 10 Feet within the Surface, beyond that Depth the Heat is more uniform; the Ther⯑mometer, at the Depth of 130 Feet, ſcarcely varying, except from accidental Cauſes from Subſtances within the Bow⯑els of the Earth. By the Relations of ſome who have gone down great Depths into the bottom of Mines, coming out of the warm Air deſcending a few Fa⯑thoms, they find themſelves colder; af⯑terwards the Heat increaſeth, as they go lower, ſo that the Labourers are forc'd to work in ſome Mines without their Clothes; and no doubt this Heat is different, according to the Difference of thoſe Mineral Subſtances. The Heat produc'd by the Action of the Sun in the ſuperficial Parts of the Earth, is longer [84] in decreaſing and increaſing, than in the Air, or in the Surface; ſo that the Sea⯑ſons within the Surface of the Earth do not begin ſo ſoon as in the open Air.

XXIII. Great Alterations are produced in the Temperature of the Air, as to Heat and Cold, by Winds; not by their Motion, but as they blow over hot or cold Grounds, and mix Air of a hotter or colder Temper, with the Air of that Place, which, as they add or ſubſtract Degrees of Heat, produce half the Sum: For Example, Air, hot as 80, mixing with Air hot as 40, makes Air hot as 60; Air, hot as 30, mix'd with Air of 40, makes Air hot as 35. There are hot Winds in Africa, which blow over ſandy Deſarts, that kill even Elephants: On the other hand, a Northerly Wind, blowing at the moderate rate of 8 Miles an Hour, would bring the Air of the Pole to London in 12 Days; for this Reaſon, in hot Climates, on this ſide the Line, Northern Winds are wholſom, and Southerly Winds bring Diſeaſes. The Sickneſs and Health of the Inhabitants of Egypt, keep regular Periods with thoſe two Winds. The Air of any Place may be heated or cool'd to great Degrees, by Winds; for, as I obſerv'd before, [85] blowing with a Bellows the Air of the Room where the Thermometer ſtands, neither raiſes nor ſinks it; but if you blow through hot Metal or Ice, the firſt raiſes and the ſecond ſinks it in a Moment. Winds cool Human Bodies, if they are cooler than the Atmoſphere of perſpirable Matter that ſurrounds them, by blowing off that hotter At⯑moſphere, and inveſting the Body with one ſomewhat cooler. The Sea and Land Breezes refreſh the Air of Countries within the torrid Zone, and are ex⯑tremely comfortable to the Inhabitants. Wherever the Air is extremely rarify'd by Heat, the neighbouring cooler Air ruſheth in to reſtore the Balance. The Nights in hot Countries are often very cold, and upon that Account extremely dangerous to the Health of ſuch as ex⯑poſe themſelves to it. An Eaſterly Wind in this Country, blows freſh after the Sun is down; and, after a hot Day, chills Human Bodies expos'd to it too much, often occaſioning Fevers and other Diſeaſes.

XXIV. In large Tracts of Land, there is a much greater Uniformity of the Weather than is commonly imagin'd; the Colds and Heats differ as to their Degrees, but begin and end much about [86] the ſame time: This is confirm'd by Journals of the Weather kept at Up⯑minſter, Zurich, and Paris; remarkable Changes of Weather happening at thoſe Places, near the ſame time. The Changes of the Gravity of the Air are yet more uniform; the Mercury, by Obſervations, riſing and falling about the ſame time at Paris, Upminſter, Dublin, Lancaſhire. The Winds likewiſe, when they are ſtrong, agree very well; when they are leſs violent, they differ, as depending upon local Cauſes. It appears likewiſe that the Alpine Snows have an Influence upon the Weather of England, as well as upon that of Zurich; the Weather being uniform in great Tracts of Grounds, makes the Diſeaſes uniform likewiſe, which we have of late ſeen by plain Obſervations.

XXV. The Cold of ſome Winters in Britain, and ſome Parts adjacent, parti⯑cularly 1708, has nearly equall'd, in its Effects, that of great Northern Lati⯑tudes, by deſtroying ſeveral Animals, as Fiſhes, and ſome ſorts of Birds, which continued ſcarce for ſome Years after⯑wards^*; but moſt of all, Vegetables; [87] and yet did not produce any great Mortality amongſt Mankind, becauſe of the artificial Defences Human Crea⯑tures uſe againſt extreme Cold: The Cauſes of thoſe great Excurſions of the Seaſons into the Extremes of Cold and Heat, are very obſcure, but ſeem ra⯑ther to depend upon Effluvia that riſe out of the Earth, than the Action of hea⯑venly Bodies.

XXVI. As to Moiſture and Dryneſs, as far as they affect Human Bodies, they are to be conſidered only in the Region of the Air in which we live and breathe; wherever there is a Cloud, there is moiſt Air, or what would feel ſo to a Human Body; but if it is at ſuch a Height as not to be contiguous, the Body is not affected with it.

XXVII. In dry Weather, the Water in the Air is intimately mix'd with it, and the Vapours being higher, do not af⯑fect Human Bodies with a Senſation of Moiſture; but when watery Vapours aſ⯑cend or deſcend in Maſſes, then they affect Human Bodies, and probably are imbib'd with the Air, which feels more moiſt when the Water is deſcending, than aſcending; more when the Water is in ſmall, than in great Drops; in meazling and ſoaking Rains, than in great [88] Showers: The Effects of Moiſture are more ſenſible to Human Bodies before, than after great Showers.

XXVIII. The Quantity of Vapour rais'd, and the Quantity of Water pre⯑cipitated from the Air, as I obſerved before, ſeems to be pretty uniform the Year round, over the Surface of the ter⯑raqueous Globe, perhaps about 22 Inches deep over the whole; but from acci⯑dental Cauſes it differs conſiderably as to Quantity, in different Places, and in the ſame Place in different Years. In a Period of Eight Years, the Quantity of Water fallen from the Clouds was obſerv'd to be,

The Quantities vary in another Cycle, but the Proportions not ſo much. The Cauſes which vary the Quantities of Rain ſeem to be 1ſt. A wetter or more watery Surface, expos'd to the Action of Heat, by which the Vapours are rais'd. 2dly. Cold in the upper Regions of the Air, to condenſe thoſe Vapours, which, [89] when they grow too heavy, muſt fall down in the Form of Rain, Hail, and Snow; therefore a moiſt Surface of Earth, with a Succeſſion of Heat and Cold, muſt neceſſarily occaſion a rainy Seaſon. 3dy. Winds, which vary the Quantity of Rain in a particular Place, by carrying the Clouds of one Place to another. Hills attract Vapours; and the Valleys near mountainous Places have generally great Quantities of Rain. As to the Moiſture and Dryneſs of Regions within the torrid Zone, the moſt gene⯑ral Rule is, That the Rain is greateſt, when the Sun is neareſt; and the Drought the greateſt, when the Sun is moſt oblique: This Joſeph d' Acoſta af⯑firms, tho' not without ſome Excep⯑tions. In our Climate, the moſt copious Showers, with the biggeſt Drops, are in the Summer. Within the Tropick the rainy Seaſon is what they call their Winter. There is perhaps a greater Quantity of Rain falls between the Tro⯑picks, than in greater Latitudes. There are greater Rivers and Lakes, and by the greater Heat, greater Quantities of Va⯑pours are rais'd. This freer Circula⯑tion of Water balanceth the great Heat, which, without Moiſture, would ren⯑der Human Bodies ſickly, and the [90] Ground unfruitful. The Moiſture of a Seaſon is not to be exactly eſtimated by the Quantity of Rain; for many rainy Days (during which the Weather may be ſaid to be moiſt) do not often produce ſo great a Quantity of Rain, as one great Shower, ſucceeded by ma⯑ny dry Days; but the Changes wrought in Human Bodies are proportional to the Continuance of moiſt or dry Sea⯑ſons. The Quantity of Water falling upon any Tract of Ground, may be e⯑ſtimated by the Condition of the Springs: where they fall, to be ſure there has been wanting a ſufficient Quantity of Water from the Clouds to ſupply them; and the Surface of the Earth is no doubt for that Reaſon dry⯑er, and ſupplies a ſmaller Quantity of Vapours. There is ſcarce any better Meaſure for the Moiſture of the Sur⯑face of the Earth, the Quantity of Va⯑pours, and in general the Moiſture of the Seaſon, than the Quantity of Wa⯑ter; and indeed this is, in Places under the Influence of variable Winds, very different in different Years; at Upmin⯑ſter, in the Year 1709, there fell of Rain more than 26 Inches; of Rain, in the Year 1714, leſs than 11⅕ Inches, above the Difference of 2 to 1; [91] at Paris, in the Year 1693, there fell 24.18; in 1705, 14.82, a Difference of near 7 to 5. Great Excurſions of the Seaſons, as to Drought and Moiſture, produce great Alterations in the Con⯑ſtitutions and Diſeaſes of Mankind; and, as far as Obſervations reach, dry Seaſons ſeem to be the moſt dangerous of the two; the Year 1714 was fatal to the Cattle for want of Water; but it was likewiſe unhealthy to Mankind, per⯑haps from the want of a due Quantity of Water in the Air.

XXIX. Moiſt Air inſinuates it ſelf into the Pores of the moſt compact Bo⯑dies; and, as was obſerv'd before, Hu⯑man Bodies abſorb it with Air; and per⯑haps a due Quantity of it is neceſſary for a right State both of the Fluids and Solids. A Spunge will increaſe 1/10 of its Weight, by the Moiſture of Air, in ſpite of a Fire in the Room; but as the Fire diminiſheth, it will acquire more Weight. Sheeps Leather imbibes the Moiſture of the Air plentifully. Bones are ſuſceptible of this Moiſture. Rots amongſt Sheep are occaſion'd by ex⯑ceſſive Moiſture in the Air. By Hygro⯑ſcopes, eſpecially thoſe made of Spunges, many uſeful Obſervations may be made as to the Weather, and its Influence on Human Bodies. By Hygroſcopes it [92] is obſerv'd, that Winds often abate the Moiſture of the Air, by blowing away the Vapours from whence they are drying; and ſo likewiſe they increaſe the Quantity of Evaporation, by blowing away the Coat of Vapours which inveſts a Surface of Water, and letting a new one ariſe.

XXX. Moiſture increaſeth the Weight and Dimenſions of vegetable Subſtances; and, as was obſerv'd, relaxeth all ſimple Fibres, both vegetable and animal; con⯑ſequently from moiſt Air may be pro⯑duc'd all the Diſeaſes which proceed from Laxity of Fibres, and ſuch muſt be the Diſeaſes and Conſtitutions of moiſt Countries and moiſt Seaſons: On the contrary, extremely dry Air ſucks up the Moiſture of animal Bodies, eſpecially combin'd with Heat; Heat relaxeth, and combin'd with Moiſture, ſtill more: Of theſe Matters I ſhall treat afterwards.

XXXI. What I obſerv'd N^o VII. Chap. II. of the great Limits ſufferable by Human Bodies, in the Weight of Air, is likewiſe true of the other Qua⯑lities of the Air: It is wonderful to obſerve one Creature, that is, Mankind, indigenous to ſo many different Cli⯑mates. Generally ſpeaking, the Animals of warm Countries cannot ſubſiſt in Cold. African Animals can hardly en⯑dure the Coldneſs of the open Air of Eng⯑land, [93] which is too warm for Rain Deer; yet a Human Creature can ſubſiſt in Air from under the Line, to perhaps 75 Degrees of Latitude. What makes the Difference between Mankind and other Animals is, that Mankind is aſſiſted by many Contrivances of Art, to bear Ex⯑tremities. Brutes, left to their own Choice, as far as they can procure their Ends by local Motion, chooſe the Countries and Climates moſt adapted to their Conſtitutions; and ſo perhaps would a Human Creature, if he were left to his own Choice; but he is in Society, and under Government, and ſubject to Paſſion, to which he ſacri⯑ficeth the greateſt Bleſſings of Health, and Life itſelf. There are likewiſe o⯑ther Cauſes of Migrations of great Herds of Mankind, which is their ſwarm⯑ing ſo as to overſtock the Countries which they inhabit.

CHAP. V. Of the Uſe and Effects of Air in Re⯑ſpiration.

I. IN order to come at the cleareſt Light poſſible in this Enquiry, it is neceſſary to ſtate Facts as they ap⯑pear by Experiments and Obſervations. All Animals live in Air or Water; or ſometimes in one, and ſometimes in the other; therefore they may be call'd, Aereal, Aquatick, or Amphibious. All Animals have ſome Organ by which they draw in and expel, by turns, ſome of the Fluid in which they live, by which the Aereal draw in Air, and the Aqua⯑tick Water: In the Aereal, this Organ is call'd Lungs; in Fiſhes, Gills. Fiſhes which ſometimes breathe Air, and can⯑not always live under Water, as the Cetaceous Kind, have Lungs, and not Gills.

II. No Animal which has once made uſe of this reciprocal Motion of Lungs or Gills, can live any conſiderable time without continuing the ſame.

III. Air is ſo neceſſary for the Life of every Animal, Aquatick, as well as Aereal, that without it Life is extinguiſh'd [95] in more or leſs time, according to their different Structure.

IV. Fiſhes in the Air-pump, as the Air is drawn out of their Water, ſwell, emit Air-bubbles, ſwim on their Backs, and at laſt die; but if freſh Air be a⯑gain admitted before they are quite dead, the Symptoms vaniſh, and they reco⯑ver. Some Fiſhes, as Carp, Tench, Eel, live longer in Air, than in Water with⯑out Air; ſome of the teſtaceous and cruſtaceous Kinds, live very long in an exhauſted Recipient; Oyſters have liv'd 24 Hours in an exhauſted Recipient; a Craw-fiſh may be kill'd in one. Aqua⯑tick Animals live longer without Air than the Amphibious, and the Amphi⯑bious longer than the Aereal; and of theſe, ſome a longer, and ſome a ſhorter time, according to the Structure of their Lungs. ^* A Duck holds out longer in an exhauſted Receiver, than a Hen. A Viper can live 2½ Hours in an exhauſt⯑ed Receiver; and a Frog as long; a Snake 10 Hours; when ſome of thoſe Animals ſeem as they were dead, they revive upon the Readmiſſion of freſh Air; but no Animal revives that has been kept in a perfect Vacuum.

[96] V. Young Animals live longer in the Air-pump than adult; a Kitling longer than a Cat; as a Foetus in the Mother's Belly, or newly excluded, may live with⯑out Air before it has breath'd.

VI. The Symptoms which Animals feel in an exhauſted Receiver, do not all proceed from the extreme Rarity or Want of Air to breathe; but many of them from the Expanſion of the Air in their Veſſels, by taking off the in⯑cumbent Preſſure, which throws them into Convulſions, from which they are reliev'd, as they emit Air out of their Bodies, as was obſerv'd before; the Ba⯑lance between the outward Air, and that within the Animal, muſt be pre⯑ſerv'd; and if this Balance is too quick⯑ly chang'd for the Capacity of thoſe Paſſages of Communication, between the external Air and the internal of the Animal, the Animal, during that time, muſt ſuffer. It was obſerv'd, that a Hu⯑man Creature, changing its Situation by degrees, can live in Air differing one half in Denſity; but in an exhauſted Recipient, ſinking the Mercurial Gage 16 Inches, would throw a Human Crea⯑ture into Convulſions by the Suddenneſs of the Change. Drowning kills Aereal Animals by depriving them of Air; if [97] the Air in Receivers could be exhauſted all at once, Want of Air would kill in the ſame time as Drowning, which, in ſome Animals, is very ſhort. Small Birds are kill'd by being kept under Water half a Minute; a Duck in 6 Minutes; yet even Water-fowl, tho' they can ſtay under Water longer than other Birds, by Particularities in their Structure, they do not bear the Want of Air much longer than other Birds.

VII. What is remarkable, not only in Reſpiration, but may perhaps take place in other Qualities of the Air, That Aſſuefaction, or being accuſtom'd, makes Animals ſtill endure thoſe Expe⯑riments better and better. A Duck, us'd to an exhauſted Receiver, can en⯑dure it longer than a freſh one. A⯑nother Fact, ſettled by a fair Experi⯑ment of the ingenious Mr. Hales, is, that the Lungs of Animals that die in Vacuo, are ſhrunk, and ſink in Water like the Lungs of a Foetus; yet the Lungs of an Animal that dy'd in Vacuo, being afterwards put into a Recipient, and the Air exhauſted, ſwell.

VIII. As no Animal can live with⯑out Air, ſo none can live long in breath⯑ing the ſame individual Air. A Gal⯑lon [98] of Air cannot ſupply a Human Creature 1 Minute: By an Experiment of the ingenious Mr. Hales, 74 cubical Inches of Air could not ſupply him Half a Minute without Uneaſineſs, and not 1 Minute without Danger of Suf⯑focation; but if he had been ſhut up with a proportional Quantity of Air, which conſequently muſt have been ſpoil'd, not only by the Steams of the Lungs, but of the whole Body, the ſame Quantity would not have ſupply'd him ſo long a time.

IX. The rarer the Air is, it is the ſooner ſpoil'd. A Linnet can live in a⯑bout Half a Gallon of Air for 3 Hours, ſick, but not quite dead; but in Air of half the Denſity, not 1¼ Hour: A Lark expired in 4½ Pints of Air, with ¾ of it exhauſted in 1⅓ Minute. Animals cannot live long in Air extremely rare. Rarity is the Want of ſo much Air.

X. The Lungs are the chief Inſtru⯑ment of Sanguification, working ſome⯑what after the manner of a Preſs, churning and mixing together the Blood and Chyle, by a reciprocal Expanſion and Dilatation, which cannot be per⯑form'd without the Admiſſion and Ex⯑pulſion of freſh Air. A Foetus, through which the Mother's Blood already ela⯑borated, [99] circulates, does not ſtand in need of ſuch an Organ; but as ſoon as the Animal wants a proper Sanguifica⯑tion, he wants the Uſe of Lungs: Ac⯑cordingly, as ſoon as the Infant is ex⯑poſed to the Air, being out of the com⯑mon Integuments, the leaſt Motion of the Muſcles of the Thorax and Dia⯑phragm muſt change the Dimenſions of the Cavity of the Thorax; upon the Enlargement of which, the Air enters by the Windpipe into the Cavity of the Lungs, which conſiſts of a Congeries of Air-bladders, dilatable by the Admiſſion, and contractable again by the Expulſion of Air; the whole Mechaniſm being no⯑thing but that of a Pair of Bellows. By this Dilatation of the Lungs, the pul⯑monary Veſſels are unfolded, and a new Paſſage for the Blood, from the right Ventricle of the Heart through the pul⯑monary Artery, is opened, and the Fo⯑ramen ovale, by which the Blood paſs'd from one Ventricle to the other, is ſhut by a Valve, and by degrees obliterated; by this Mechaniſm, the Blood refluent into the right Ventricle of the Heart, continues to circulate through the Lungs as long as Reſpiration, or the recipro⯑cal Motion of Expanſion and Contrac⯑tion of the Lungs is continued; but [100] that ceaſing, the Circulation through the Lungs, which begins with Reſpiration, muſt likewiſe end with it, and the Blood, in Quantity Half of that of the whole Body, is at this time depriv'd of its Paſſage by the Foramen ovale, and being ſtopt, the Animal muſt die. Thus the Animal being totally depriv'd of Air to perform Reſpiration, as in an exhauſt⯑ed Receiver, muſt die: The flaccid State of the Lungs, and their being more ponderous than Lungs in their na⯑tural State, as by N^o VII. demonſtrate this to be the Caſe, and that the Blood ſtagnates in the Veſſels. The Blood-Veſſels creep along the Surface of the Air-bladders, upon the Dilatation of the Air-bladders; they muſt be unfolded and lengthened, whereas in a collapſed State they are corrugated, and as it were folded; yet warm Water can be ea⯑ſily injected into the Lungs in a collapſed State.

XI. The Capacity of a Human Lungs full grown, or the Sum of the Capacity of all the Air-bladders, is at leaſt 220 cubical Inches; for ſo much Air is poſſi⯑ble to be taken in at one Inſpiration, by an Experiment of the learned and accu⯑rate Dr. Jurin. The Quantity of Air taken in by a common Inſpiration, is [101] various in different Subjects and Times, but hardly reaches 40 Inches, perhaps at a Medium 20, at which Rate 10/11 Parts of the Cavity of the Lungs continue full of Air, or ſome other Fluid, after every Expiration. The Surface of the Veſicles of the Lungs of a Human Creature is much larger than the whole Surface of the Skin, by a Menſuration and Calculation of Mr. Hales. The Surface of the Lungs of a Calf bears a Proportion to that of its whole Body, as 10 to 1.

XII. The Blood in the Lungs is warmer than on the Surface of the Skin; the Coat of the Veſſels extremely thin, and thoſe expos'd to the outward Air; and yet the Perſpiration from the Lungs is not half of that from the Skin. Q. What is the Reaſon of this ſmall Proportion? Is the Air abſorb'd? for the Quantity of Perſpiration is the Difference between the Air abſorb'd, and the Humour prepar'd. There are ſeve⯑ral things may be ſaid for and againſt the Air's entering into the Blood-Veſſels of the Lungs in Reſpiration. 1. From the flaccid State of the Lungs of Ani⯑mals that die in Vacuo, it ſeems evident that the Lungs do not expand themſelves [102] upon the Exſuction of the Air, conſe⯑quently the Air is ſuck'd out or eſcapes through the Blood-Veſſels of the Lungs; elſe if retain'd, it would expand and ſwell them; if the Air has a free Egreſs through the Coats of the Veſſels of the Lungs, it may have a free Ingreſs. On the other hand, Attempts to force Air into the Blood-Veſſels of the Lungs by the Wind-pipe, have prov'd unſucceſsful, and the Lungs of Animals that die in Vacuo, afterwards ſwell in the Air-pump. Things may happen in a live Animal, which will not ſucceed in a dead one. Air will paſs through any Membrane, when moiſt. The quick Reſtoration of the Balance of Air with⯑in and without Human Bodies, ſhews that there is a free Communication; and it is probable that it is ſo in the Lungs, as well as in other Parts of the Body.

XIII. By N^o VIII. of this Chapter, the Air is quickly ſpoil'd by the Fumes of the Lungs, ſo as to render it unfit for Reſpiration: This muſt happen from ſeveral Cauſes; the Groſneſs of the Vapours hinders the Ingreſs of the ſubtler Parts of the Air into the Veſi⯑cles, which are ſo ſmall as hardly to be [103] diſcern'd by a Microſcope. If there be any Salts in any ſort of Fumes, they muſt contract the Veſicles, and per⯑haps the tainted Air may likewiſe affect the Lungs by its Heat. Another Cauſe is the Deſtruction of the Elaſticity of the Air by ſulphureous Steams. Animal Steams are ſulphureous, and as ſuch, in⯑flammable. The Senſation felt upon breathing Air tainted already with your Breath, is like that after a ſtrong Expiration, and the Lungs feel as they were much fall'n, the Air not entering into them by the Loſs of Elaſticity, by which it ruſheth into any Vacuity; al⯑lowing 20 Inſpirations for 1 Minute, and 20 cubical Inches of Air for every Inſpiration, this would make 24000 cu⯑bical Inches of Air in an Hour; ſome of the elaſtick Power of the Air is de⯑ſtroy'd at every Inſpiration by the ſul⯑phureous Vapours lodg'd amongſt the Air-bladders; and ſuppoſing the ſame numerical Air to be inſpired, the 24000 cubical Inches of Air would loſe ſo much of its Elaſticity as to render it unfit for Reſpiration.

XIV. Vapours abſorb true Air, or deſtroy its elaſtick Force at a great Rate: But the Loſs of Elaſticity is not the ſole Cauſe of Air tainted being un⯑fit [104] for Reſpiration. ^* A Rat liv'd 14 Hours in 2024 Inches of Air, during which time 1/27 of the whole was ab⯑ſorb'd. A Cat, 3 Months old, liv'd an Hour in 594 cubical Inches of Air, with the Loſs of 1/30 of true Air; and 19 Parts in 20 of the Air of de⯑toniz'd Nitre is deſtroy'd in 18 Days. The Air produc'd by Diſtillations, loſes its Elaſticity. Burning Matches deſtroy the Elaſticity of the Air at a great Rate. The Air, generated from fermenting ſulphureous Mixtures, is quickly abſorb'd, as in burning of Filings of Iron and Brimſtone, Antimony and Brimſtone. The Lungs, and all the Parts of the Thorax, undoubtedly perſpire; if this perſpirable Matter retain'd any Elaſticity, it would be a Counterpoiſe to the out⯑ward Air, and ſtop the Expanſion of the Lungs, as much as a Wound in the Thorax ſtops the Reſpiration of that Lobe, till the outward Air is excluded. The Air therefore in the perſpirable Matter of the Thorax is abſorb'd, and the Steam is unelaſtick. Sulphureous Va⯑pours deſtroy elaſtick Air only to a cer⯑tain Degree, for when Air is ſaturated with Vapours to a certain Quantity, no [105] more elaſtick Air is abſorb'd, which is a happy Contrivance of Nature, elſe the Air, for a great Extent, might be ſpoil'd with ſulphureous Steams. But tho' the Elaſticity of the Air is never totally de⯑ſtroy'd, the ſame once deſtroy'd is never recover'd, yet in ſome Caſes this Ab⯑ſorption of Air will reach to a great Degree. The Suffocation of Animals and the Extinction of Candles in Mines, proceed from ſulphureous Vapours. Mr. Hales has found out the beſt Expedients for preventing immediate Suffocation from tainted Air, and to enable a Man to ſuſ⯑tain it a longer time, in Caſe of Neceſſi⯑ty, which is by breathing through Muf⯑flers, which imbibes theſe Vapours; and this anſwers Experience, for the Mufflers increaſe in Weight by the Vapours which they imbibe. Salts are likewiſe ſtrong Imbibers of ſulphureous Steams; therefore he combin'd both theſe Subſtances toge⯑ther, and by dipping his Mufflers in a Solution of Sea-Salt, Salt of Tartar, or White-wine Vinegar, he was able ſtill to breathe longer in this tainted Air. Steams of Vinegar are reckon'd Antipeſtilential; and for the ſame Reaſon Salts may be ſo, by ſucking up the noxious Vapours. In Salt Mines, great Numbers of People live in good Health, who never breathe [106] the Air above-ground: It ſeems likewiſe to follow from this Experiment, that a Room hung with ſome Woollen Manu⯑facture, muſt be wholſom, by imbibing the Steams of Animals, Fire and Can⯑dles, or any noxious Vapours.

XV. From the foregoing Experiments, a natural Account may be given of the Sufferings of People who paſs a long time in a Room overcharg'd with the Steams of Animals, Fire and Candles. A Gallon of Air is ſpoil'd by the Steams of the Breath in one Minute, ſo as to be unfit for Reſpiration; conſequently a Tun, or 63 Gallons, would not ſupply a Human Creature an Hour; if he was ſhut up in this Tun of Air, the Air would be tainted by the Steams of the whole Body in ⅓ of the Time, or about 20 Minutes: And I believe it anſwers Experience, that a Human Creature could not live in a Tun of the ſame Air 20 Minutes; conſequently 500 Peo⯑ple, ſhut up in a Room of 500 Tun Capacity, ſo as to have no Communica⯑tion with the outward Air, would be dead, or in Convulſions, and other fatal Symptoms, in 20 Minutes; or in a Room of 3000 Tun Capacity, in 2 Hours: This is indeed never the Caſe; and there is always in every Room ſome [107] Vents for the inward Air, and Inlets for the outward Air; notwithſtanding which, the Air is much tainted, and tho' it is not fatal, it is hurtful. La⯑dies, and other tender People, paſs a great Part of their Time in Rooms ex⯑tremely well fitted up, ſo as to admit ſcarcely any outward Air, except by o⯑pening of Doors and Windows; the Air of the Room is tainted very much with the Steams of Animals and Candles. Q. Whether ſome of their nervous Symp⯑toms may not proceed from this Cauſe? Fire and Candles taint the Air, a middle-ſiz'd Candle as much as a Human Creature, and are as ſoon extinct by ſul⯑phureous Steams, and by the Deſtruction of the elaſtick Force of the Air; there⯑fore Fire, fed by cool Air, burns moſt briskly, and moſt of all in a keen Froſt: Heat, by weakening the Spring of the Air, abates the Force of Fire; the Light of the Sun will put out a Fire; and a ſmall Fire will not burn near a large one. ^* Fire ſeems to be produc'd by the Ac⯑tion and Reaction of Sulphur and Air; for Salt, Water, and Earth, are not in⯑flammable. There is ſomething analo⯑gous [108] to this in Human Creatures. Air, weaken'd in its Spring, is not ſo fit for Reſpiration, nor perhaps for any other animal Purpoſes. We find by Experience, that Aſthmaticks cannot bear the Air of hot Rooms and Cities where there is a great deal of Fuel burnt, except in Sum⯑mer, when the Conſumption of Fuel is leſs.

XVI. As to the Force or Preſſure of the outward Air upon the Lungs, it is not ſo great as has been calculated by ſome, whoſe Calculations have been rec⯑tify'd by one of Dr. Jurin's, who makes the Preſſure of the Air upon the Lungs not much more than that of falling Dew. The Force of a Smith's Bellows will raiſe Mercury one Inch; a Bellows has but one Air-bladder, and a Human Lungs Millions; and it requires a great⯑er Force to draw in and expel the Air, through a Capacity of 220 cubical Inches, diſtributed into Millions of little Cells, than through one Cell of the Capacity of 220 cubical Inches; the Friction in the firſt Caſe muſt be very conſiderable; it requires a conſiderable Force to move a Pair of Bellows of the Capacity of a Human Lungs, with a Noſe of the Ca⯑pacity of the Wind-pipe, and would re⯑quire ſtill more, if they were divided in⯑to [109] as many Cells as a Human Lungs: Therefore it ſeems to me, that the Force of the Air upon the Lungs is at leaſt 1/30 of the Weight of the Atmoſphere; but whatever be the Force of the Air upon the Lungs, it varies with its Gravity and Elaſticity, conſequently the Variation of thoſe muſt have proportional Effects up⯑on the Motion of the Blood through the Lungs. The Expanſion of the Lungs by Reſpiration being neceſſary for the Circulation through the Lungs. The Circulation is more eaſy, in Proportion to that Expanſion; on the contrary, whatever ſtops the Circulation through the Lungs, muſt hinder the Dilatation, by which it is plain, Reſpiration muſt have an Influence upon the Pulſe, as to Frequency, Strength, Hardneſs, or Soft⯑neſs: Whether it bears any Proportion as to Time, I leave to be determin'd by future Obſervations: As far as I have obſerv'd, the Frequency of a natural Pulſe, is to that of Reſpiration, about 10 to 3; this I ſuggeſt only, as a Matter worth the inquiring into. Too great Repletion, or too great Emptineſs of the Lungs, occaſion a quick Pulſe. The Increaſe of the Frequency of the Pulſe in Animals dying by Loſs of Blood, is a very curious Experiment of the inge⯑nious [110] Mr. Hales. A ſmaller Quantity of Blood circulates with greater Eaſe through the Lungs; in which Caſe the Heart acts like a voluntary Agent, who when there is a leſs Weight of the Fluid to be forced through Pipes by pumping, is able to redouble its Strokes. The Ex⯑periments and Calculations about the Force of the Heart in propelling the Blood, do not determine its abſolute Force, but only that which it exerts in that Circumſtance: The Heart employs various Degrees of Force to carry on the Circulation, and preſerve the Life of the Animal, according to the Quan⯑tity of Reſiſtance: But whatever the Preſſure of the Air is upon the Lungs, it is diminiſh'd and increas'd in Pro⯑portion to its Denſity. Some have ſup⯑pos'd the Weight of the Atmoſphere to be the Antagoniſt Force to the Muſcles, which dilate the Thorax; but the Re⯑ſiſtance of the Air to any Motion is ſo ſmall, that it may be reckon'd nothing; and when the Inſpiration is ended, the external Air, and that within the Lungs, are equally balanc'd, and the Air can have no Force in relaxing thoſe Muſcles. An ingenious Countryman of mine has given a Solution of this Motion of Reſtitu⯑tion, which I have not yet examin'd. [111] The Action of Reſpiration is in ſome meaſure ſubject to the Will, for it can be ſuſpended for ſome time; and there are Inſtances, one at leaſt, that I have heard, of a voluntary Suffocation, by holding the Breath. Reſpiration being carried on in Sleep is no Argument a⯑gainſt its being Voluntary. What ſhall we ſay of the Noctambulos? There are voluntary Motions carried on without Thought, to avoid Pain.

XVII. The Cauſes of a faulty Reſpi⯑ration are multifarious; whatever creates any Degree of Immobility in the Tho⯑rax, as Stiffneſs in the Motion of the Ribs or Cartilages, and conſequently a⯑bates the Quantity of its Dilatation, in Proportion to which, a ſmaller Quantity of Air muſt enter the Lungs: Fullneſs from any Cauſe, even from Wind in the lower Belly, which preſſing upon the Diaphragm, reſiſts its Contraction, by which the Cavi⯑ty of the Thorax is enlarg'd; Repletion or Obſtruction of the Veſſels of the Lungs; Humidity of any kind, in the Cavity of the Air-bladders; Contraction of their Fibres from any ſaline Stimulus. Theſe Cauſes, by diminiſhing the Cavity of the Air-bladders, muſt proportionally abate the Quantity of the Air inſpir'd: Likewiſe all inflammatory and ſtimula⯑ting [112] Cauſes, which diſturb the Motion of the Muſcles, Membranes, and other Organs of Reſpiration; ſuch are an Impediment to Reſpiration, by making a full Reſpiration painful. Laſtly, Such Cauſes as ariſe from the Qualities of the Air, as ſulphureous Steams, or too great Heat, which deſtroy its Elaſticity, or render it too groſs to enter the Air-blad⯑ders: Watery Vapours, the leaſt Quan⯑tity of Water entering the Wind-pipe, muſt be immediately rejected by Cough⯑ing: Acid Mineral Steams, which imme⯑diately contract the Fibres of the Bron⯑chia, and coagulate the Blood; and many others, too long to enumerate, but per⯑haps reducible to ſome of the abovemen⯑tion'd Heads.

XVIII. Such as have a faulty Reſpira⯑tion, muſt neceſſarily have an imperfect Sanguification. The Blood of Aſthma⯑ticks is viſcid, and imperfectly mixt, being not ſufficiently attenuated by the Action of the Lungs; and being imper⯑fectly mixt, the ſerous Part is eaſily ſe⯑parated from the globular; for ſlow Mo⯑tion approacheth to a quieſcent State, in which the Serum is intirely ſeparated from the Craſſamentum. The ſecondary Uſes of Air in Reſpiration, to form the Voice and Speech, to perform Suction, or taking [113] of Aliment, Expulſion of the Faeces, &c. refrigerate the Blood in the Lungs, by what was obſerv'd N^o VIII. Chap. III. Animals cannot breathe Air much warmer than the natural Heat of their Body, for ſuch Air reduceth their Fluids to a State of Putrefaction. If a Human Creature is depriv'd of this Refrigeration by cool Air for a Moment, by holding his Breath, he grows hot in Proportion; the whole Maſs of Blood circulates through the Lungs in 10 Minutes; the Blood moves in the ſmall Veſſels of the Lungs 43 times faſter than in the Capillaries of o⯑ther Parts of the Body; the Attrition is greater in the Lungs than in any other of the Viſcera, becauſe the Lungs work as a Preſs, and are conſtantly kneading or churning the Blood; the Attrition of the Blood by the Surfaces of the capillary Veſſels, through which it flows, is, caete⯑ris paribus, in the inverſe Proportion of the Diameters; but by this Attrition the Blood is retarded, and the Capillaries ac⯑quire a greater Plenitude, which ſerves many Purpoſes of Nature. Without this Refrigeration by cool Air, the Blood in the Lungs would grow extremely hot.

XIX. The Lungs of cold Animals, ſuch as Serpents, Frogs, &c. conſiſt of larger and leſs numerous Air-bladders, [114] than thoſe of warm Animals, for which Reaſon, in theſe, the Attrition on the Lungs is greater, the Blood warmer, the Perſpiration greater, and conſequently a more conſtant Reparation by Aliment ne⯑ceſſary. Serpents can live long without Aliment. A Degree of Heat, beyond that of the Element in which they live, is neceſſary for all Animals. The Blood of Fiſhes has ſome Degree of Warmth beyond that of the Water in which they live. A certain Degree of Heat is ne⯑ceſſary to keep the Blood from coagula⯑ting, and too great a Degree of Heat ac⯑tually coagulates; that of a Human Crea⯑ture approaches very near the Degree of Coagulation. But this Heat of the Blood does not proceed merely from the ſaline ſulphureous Parts that are in it, for Fiſhes have rather more Salt and Oil in their Blood, than terreſtrial Animals. The Heat of the Blood is the Effect of Motion and Attrition of elaſtick Particles, and for that Reaſon is greater in the Lungs, than in any other Organ; no doubt the ſaline and oily Parts, of which the Blood conſiſts, makes it more ſuſceptible of Heat by Motion, than a mere watery Fluid.

XX. Tho' we have endeavour'd to ex⯑plain the Uſe and Effects of Air in Re⯑ſpiration, as far as is obvious to our [115] Senſes, and deducible from mechanical Principles, we are far from imagining that Air has not many Uſes and Effects in the Animal Oeconomy, which we ſhall never be able to account for; and that there is in it ſome other vital Principle, which makes it ſo neceſſary for the Life of all Animals. Air con⯑vey'd by other Paſſages than the Lungs, as into the Vena cava, Ductus Thoracicus, and even by the Anus into the Inteſtines, will reſtore the Motion of the Heart in agonizing Animals. The Motion of the Hearts of Animals, cut out of their Bodies, and the Motion of Inſects which continue ſome time after their Heads are cut off, ceaſe in Vacuo immediately. Hip⯑pocrates imagin'd the Air to be the Prin⯑ciple of animal Motion^*. Animal Life is preſently extinguiſh'd without Com⯑munication with the outward Air, and may inſtantly be reſtor'd by it. All Ani⯑mals have ſome Paſſages to inſpire the outward Air. Some Inſects have their Windpipes on the Surface ^† of their Bo⯑dy, and are therefore kill'd by the Con⯑tact of Oil, not as a Poiſon, but as it excludes the Air. Borelli ſuppoſes that [116] the Air inſpir'd by an Oſcillation de⯑pending upon its Elaſticity, regulates the Animal Motions as a Pendulum of a Clock. This Hypotheſis is ſubject to many Difficulties. Air in Liquors does not exert its Elaſticity till collected in Maſſes; it has always the Power of ex⯑erting it, but till a certain Quantity of the incumbent Preſſure is taken off, it continues in a fixed State, and divided into its minuteſt Parts. Many have en⯑deavoured to explain this vital Force of Air, I think unſucceſsfully; therefore I would adviſe ſuch as deal in thoſe Sub⯑jects to be contented to reaſon from the ſenſible Effects of Air, of which they are ſure from Experience. The Lungs being of a lax delicate Texture, with a Surface of a larger Extent than of the whole Skin expos'd to the outward Air, and of a much hotter Temperature, muſt be extremely ſenſible of the Qua⯑lities of the outward Air, and affected by them as by outward Contact; there⯑fore the Choice of Air to People of ten⯑der Lungs, is a Matter of great Impor⯑tance: Firſt, as to Humidity, the leaſt Quantity of it muſt produce a Cough; as for hot Air, the Lungs cannot bear Air that is hotter than the Animal Fluids; Heat and Moiſture together, produce [117] Putrefaction. Conſumptive People often die in a hot Day: But thoſe two Quali⯑ties ſeldom reſide long in Air together. It ought likewiſe to be conſider'd, that Heating-Rooms, by any Contrivance which does not let the Vapours eſcape, may be dangerous to the Lungs: On the con⯑trary, Air intenſely cold, by its Contact, may condenſe and coagulate the Blood, through the thin Coats of the Veſſels, ſo as to produce Inflammations, which reign here in the Winter, and in many Coun⯑tries upon cold Blaſts. We have ſeen the Effects of ſome cold and moiſt Exhala⯑tions in two epidemical Cartarrhous Fe⯑vers. Air dry, and not intenſely hot, muſt be favourable to the Lungs; accord⯑ingly Countries, where the Air has thoſe Qualities, are pretty free from Pulmonick Conſumptions.

XXI. Beſides theſe ſenſible and varia⯑ble Qualities of the Air, there may be ſaline Exhalations, which muſt affect the Lungs ſtill in a greater Degree; not only contracting the Air-Bladders, but corro⯑ding the Solids, and coagulating the Flu⯑ids. It ſeems probable, that there are a great many ſuch Exhalations in Britain, for it abounds with Mineral Waters; ſuch as is the Water, ſuch is the Air. The Air of Holland is more benign to [118] tender Lungs, than that of England, tho' it muſt neceſſarily be moiſter; but it is free from Mineral Steams, of which there are none in the Country. The Lungs being the chief Organ of Sangui⯑fication, good Air muſt help the ſecond Digeſtion; and we often feel the Effects of good Air, as well in Stomachick as in Pectoral Caſes. In ſhort, Air has ſo great an Influence, both upon the Fluids and Solids of Human Bodies, that it is Matter of Experience that ſome People find themſelves much diſorder'd in one ſort of Air and Weather, and perfectly well in another; the Cauſe of which Change is eaſily diſcoverable by any Per⯑ſon who underſtands the Phyſiology of Air, and the Conſtitution of the Patient; and for this ſingle Reaſon, the Nature and Effects of Air are a very proper Subject of Study, becauſe the Choice of it is often a neceſſary Part of Advice. The Effects of Air, when it enters the Tho⯑rax by an Aperture, are very much to be regarded in the Management of Wounds in the Thorax; for firſt, the Air which enters into the Thorax, is a Counterpoiſe to that which enters by Inſpiration, and muſt ſtop the Expanſion of that Lobe of the Lungs where the Appetite is. The Air entering into the Cavity of [119] the Thorax, corrupts and converts into Pus, Blood, and other animal Juices. If there is a Communication through the Lungs with the Air, admitted by Reſpi⯑ration, it may produce bad Symptoms, and even Suffocation; tho' the Caſe ſel⯑dom happens. It has therefore been the Practice of judicious Chirurgeons, not to dreſs ſuch Wounds with large Tents, which, amongſt other Inconveniencies, have that of admitting Air at every Dreſ⯑ſing.

CHAP VI. Concerning the Inſluence of the Air on Hu⯑man Conſtitutions and Diſeaſes.

I. THOUGH I have given ſome general Obſervations and Rea⯑ſonings on this Subject as I went on, in the foregoing Part of this Eſſay, yet I think it demands a particular Conſider⯑ation. The Effects of the Air on Human Bodies are as various as the Diverſity of the Weather, Climates and Countries. The Phyſiology of them is very obſcure and imperfect, not only in that Part which will be always hard to find out, [120] viz. the different Qualities of Air, and the Manner of their Action upon Hu⯑man Bodies; but in that likewiſe which lies within the Compaſs of Human In⯑duſtry and Sagacity. A Hiſtory of Facts, or a Journal of Diſeaſes, compar'd with the Weather, which, if it ſhould be kept for any great Period of Time, and in ma⯑ny Places, I will venture to affirm, that Mankind would arrive at more than a conjectural Knowledge in this Matter. The ancient Phyſicians ſeem to have been more attentive to this, than the Moderns; and thoſe of the Moderns who have at⯑tended to it, have perhaps made no inconſiderable Figure in their Profeſ⯑ſion.

II. Hippocrates thinks it incumbent on a Phyſician ^* to conſider the Situation, Air, and Water of a City, in order to come at the Knowledge of their popular Di⯑ſeaſes, and their Seaſons; and his own Obſervations are very particular, and ſup⯑poſe the Attraction of Air by Human Bodies: For Inſtance, That Cities ex⯑pos'd to the Sun and Winds being well perflated, at the ſame time ſupply'd with wholſom Water, are exempt from many [121] Diſeaſes, which thoſe in different Cir⯑cumſtances are ſubject to: That Cities in Greece, ſhut up from Northerly Winds, were unhealthy: That in a dry Sum⯑mer Diſeaſes end ſooner than in a wet one, in which they are obſtinate, and diſpos'd to Suppurations, Heat and Moi⯑ſture in the Air producing Putrefaction: That cold Air occaſions Defluxions and Hoarſeneſs: That ſerous Defluxions, and redundant Pituite, were the Product of the Winter, which made Women ſub⯑ject to Abortions, Children to Convul⯑ſions, and ſuch as were expos'd to Cold ſubject to Inflammations of the Eyes and Lungs. This ſagacious great Man pre⯑tends, that he could predict the Diſea⯑ſes from the Weather; and contrariwiſe, That Heat enſuing upon a wet Seaſon produceth ſerous Defluxions upon the Head and Belly, and acute Fevers: That cool Weather about the Dog-Days, if it is not ſucceeded by a temperate Autumn, is dangerous for Women and Children, producing Quartans, and the Conſe⯑quence of them Dropſies: A mild rainy Winter, ſucceeded by Northerly Winds in the Spring, dangerous to childing Wo⯑men, producing Defluxions on the Lungs, Colicks in the Phlegmatick, and Inflam⯑mations in the Bilious; that Obſtructions [122] after Relaxations occaſion Palſies and ſudden Death to old People: A rainy Spring and Autumn make a ſickly Win⯑ter; burning Fevers in middle-ag'd Peo⯑ple and Phlegmatick, Pleuriſies and In⯑flammations of the Lungs in the Bilious: A dry Summer, with Northerly Winds, ſucceeded by a wet Autumn, Head-Aches, Apoplexies: A dry Autumn with North⯑erly Winds, profitable to Phlegmatick, but dangerous to Bilious Conſtitutions, becauſe the watery Parts which dilute the Gall are abſorb'd. No leſs judicious are all his Obſervations upon the Diſeaſes of the Seaſon of the Year, as they de⯑pend upon the Temperature of the Air. He adviſeth to conſider the Conſtitution of the Air in Chirurgical Operations; ex⯑cepts againſt the Solſtices in cutting for the Stone. What he ſays about the Equi⯑noxes, and Riſing and Setting of the Stars, ſeems to be fanciful, conformable to the Opinions of that Age. This great Man goes ſtill further; he aſcribes the diffe⯑rent Shapes, Complexions, Tempers, of Mankind, and even their different Forms of Government, to the Difference of the Conſtitution of the Air: That the fertile Countries of Aſia, from moderate Heat and Moiſture, produce Animals large and handſom: That the Mildneſs of their [123] Climate diſpoſeth them to be ſoft and effeminate, not enduring Labour and Hardſhip, like the Greeks (frequent Changes in the Body affecting the Mind) from thence the Aſiaticks are leſs bold and courageous, ſlaviſh, and ſubject to Maſters, and therefore eaſily ſlide into Monarchies; that tho' they are forc'd, they are not willing to abandon their Eaſe and Families, or to hazard their Lives for the Power and Wealth of their Maſters, in Expeditions from which themſelves reap no Advantage: That on the other hand, the Greeks and North⯑ern Aſiaticks were bold, hardy, and warlike; and being their own Maſters, willingly underwent Dangers, of which they themſelves reap the Advantage. Afterwards, on the ſame Subject, he writes to this purpoſe: That as the Equability of the Temperature of the Air render'd the Aſiaticks lazy, the great Variety of Heat and Cold in Eu⯑rope, by variouſly affecting the Body, likewiſe affected the Mind, rendering them active; Activity begetting Forti⯑tude, and Fortitude begetting Laws to ſecure their Property, and being go⯑vern'd by Laws, they were ſuſceptible of the Rewards and Fruits of their In⯑duſtry, of which ſuch as live under abſo⯑lute [124] Monarchs are not. This good old Man ſeems to have been no Friend to Monarchy. The Phaſians, ſays he, from the exceſſive Moiſture of their Air, are tall, ſoft, bloated, pale; there can be no better Philoſophy than this, for ſuch Effects proceed from lax Fibres, and lax Fibres from exceſſive Moiſture. Such as inhabit mountainous Places, are fierce and active; and contrariwiſe, the Inha⯑bitants of fertile Plains, with ſtagnating Waters. Inhabitants of barren and dry Ground are proud and obſtinate. A fat Soil produceth a fat Underſtanding. A barren Soil, with cold Winters, makes the Inhabitants haſty and warm in their Tempers, proud, and quick of Appre⯑henſion. In this Book, De Flatibus, (if it be his) he aſcribes the Cauſes of all Diſtempers, eſpecially of the Peſtilential, to the Air. In his Book De Morbo ſa⯑cro, he goes ſtill further, and aſſerts, That Air gives Senſation, Life, and Mo⯑tion to the Members.

III. His moſt excellent Books of epi⯑demical Diſeaſes, are a Hiſtory of Diſ⯑eaſes, and the Weather from whence he drew many of the forementioned and other Obſervations; and through the whole, one may obſerve a great Con⯑formity between the Conſtitution of the [125] Air, and that of Diſeaſes, of which one could give not a few Inſtances. The Conſtitution of his firſt Section, a wet Autumn, dry Winter with Northerly Winds, a cold Spring, a mild Summer; from whence he obſerv'd few Suppura⯑tions. The Conſtitution of his Second Section, a moiſt Autumn, a Winter moiſt and afterwards cold, a cold Northerly Spring; the natural Product of ſuch a cold moiſt Year, were Inflammations of the Eyes, Colicks, Fluxes of the Bel⯑ly, great Fluidity, catarrhous Fevers, few continued Fevers, Tertians, Semi-Tertians, ſome Quartans, no great Thirſt, or Haemorrages attending Fe⯑vers, Catarrhs, Defluxions upon the Joints; in ſhort, all the Effects of moiſt Air, imbib'd by Human Bodies. What ſeems remarkable in the Conſtitution of his Third Section, is an Exceſs of Drought, a dry cold Winter, Spring, and Summer: This Year was noted for Palſies, (as the laſt, after a great Drought, was in London) Dyſenteries, Haemorrages of all ſorts, the Effect of a Stricture of the Fibres from Cold and Drought, continued Fevers with Deli⯑rium and Thirſt, the Diſeaſes moſt dan⯑gerous to the Young and Vigorous; great and repeated feveriſh Rigors, both [126] in Winter and Summer which were cold. In his Second Book he aſcribes the great Ri [...]neſs of Carbuncles in the Summer, to the great Heats; and obſerves, that Sweats enſued upon Showers, Moiſture relaxing; that burning Fevers were moſt violent in a hot and dry Summer; that in conſtant Weather the Diſeaſes are more uniform, and more eaſily reſolv'd; and contrariwiſe, in variable Weather, that the Diſeaſes of the Spring are leaſt pernicious. In this Book he likewiſe obſerves, That a mild Winter, with Southerly Winds, a dry Spring, and a Summer with meazling Rains like Dew, were attended with Fevers, and Paro⯑tids, or Tumors behind the Ears. A ſort of a Peſtilential Seaſon, deſcrib'd in his Third Section of his Third Book, was a hard Winter, ſucceeded by a rainy warm Spring, and an extremely hot Summer, without Winds, not very un⯑like the Conſtitution of the Year of the Plague of London: This Year, deſcrib'd by Hippocrates, was remarkable for all inflammatory Eruptions upon the Skin, and all Diſeaſes of Putrefaction. In the Sixth Book he obſerves, That frequent Changes of the Winds from North to South, produce Inflammations of the Lungs; and in general, that the proper [127] Weather of the Seaſon, as it happens later or ſooner, dry, cold, hot, with or without Winds, determine the Nature of the Diſeaſes. Theſe are a few In⯑ſtances of the Sagacity and Induſtry of this great Man, and his great Applica⯑tion to this Part of his Profeſſion, of the Influence of the Air upon Human Conſtitutions, in which, no queſtion, he was aſſiſted by the Obſervations of his Predeceſſors; and I hope to ſhew in the Sequel of this Chapter, that a great many of his Obſervations, even thoſe that ſeem moſt fanciful, depend upon na⯑tural Cauſes adequate to their Effects.

IV. As I obſerv'd before, the Subject of the Influence of Air upon the Con⯑ſtitutions and Diſeaſes of Human Bo⯑dies, has not been treated of by modern Phyſicians, with that Accuracy it de⯑ſerves; Obſervations of that kind are but few, and there is no Series of them in any Country: What would give moſt Light into this Matter, is a Collection of Obſervations in Countries where both the Qualities of the Air have great Ex⯑curſions towards Extremes, where the Seaſons, and theſe Excurſions, and the Diſeaſes depending upon them, are re⯑gular: Aegypt is a Country which an⯑ſwers all thoſe Intentions in ſome De⯑gree; [128] and it happens luckily, that a ve⯑ry eminent Phyſician, who liv'd ſome time and practis'd among them, has given us a very good Account, both of the Conſtitution of their Seaſons, and their popular Diſeaſes.

V. Egypt is ſituated between Aethio⯑pia, the Mediterranean Sea, Arabia, and Barbary, which lie in the Order men⯑tion'd, South, North, Eaſt, and Weſt of it. Grand Cairo, where Proſper Alpi⯑nus preach'd, lies in 30 Degrees North⯑ern Latitude, as Ptolemy ſays, 6 Degrees beyond the Tropick of Cancer; who for that Reaſon muſt ſuppoſe the An⯑gle of the Equator, with the Eclyptick, 24 Degrees 30 Minutes more than it is now obſerv'd to be. This great City is ſituated at the Foot of the Mountains of the Story Arabia, which lie towards the Eaſt. It is quite expos'd to the Northerly Winds which blow over the Mediterranean: Towards the South there is a hot ſandy Soil; ſo that the Altera⯑tions of Heat and Cold, as the Winds blow North and South over the Medi⯑terranean, or over this hot Sand, are exceſſive; and the Alterations of Heat and Cold from the other Winds but ſmall, lying near the Tropick; the Soil being ſandy, and fructify'd only by the [129] Slime of the Nile, without Rain; there is hardly any humid Perſpiration from the Ground itſelf, the Air receiving Moiſture only from the watery Surface of the Nile, during the Inundation, or from the Vapours brought from the Me⯑diterraneah by the Northerly Winds: From theſe Cauſes the Air is extreme⯑ly hot, and the Tropical Heats would be inſufferable, if it were not for the Northerly Winds; and indeed, the Heats are ſometimes ſo vehement, that the In⯑habitants defend themſelves from them by many Contrivances, Fountains in the middle of their Houſes, Pipes to con⯑vey freſh Air by Grottos, and high Edifices by which their Streets are ſha⯑dow'd from the Sun, and a temperate Di⯑et; and during the Tropical Heats, the Air is ſometimes ſo much moiſten'd and cool'd by the Northerly Winds, and the watery Surface of the Nile, that the acute and peſtilential Diſtempers are check'd by this Conſtitution of the Air. The Inhabitants often ſuffer from Ca⯑tarrhous Diſtempers, more than in North⯑ern Countries, their Bodies being more delicate, and their Pores more open, by the preceding Heat. As to their Seaſons, their Spring laſts from the Beginning of January to March; their Summer is [130] double; the Firſt, from the Beginning of March to the Solſtice; and the Second, from the Solſtice to the Beginning of September; and this ſecond Summer is more conſtant, healthy, and leſs ſcorch⯑ing than the firſt, by reaſon of the Dif⯑ference of the Winds, and other Cauſes after-mentioned. Their Autumn laſts Sep⯑tember and October; and their Winter No⯑vember and December. The extreme Heat of the firſt Summer proceeds from the hot Winds which blow from the South and South-Eaſt, call'd by the Inhabi⯑tants Campſin, from their Continuance of 50 Days; tho' they have no deter⯑min'd time, but laſt ſometimes more than 3 Months, and reign commonly March, April, and May; they blow o⯑ver the Sands, which they raiſe in Clouds, ſometimes ſo as to obſcure the Sun: During this time, many epidemical Diſ⯑eaſes rage, eſpecially Inflammations of the Eyes; a Fever, which the Inhabi⯑tants call D [...]melmuia, attended with a De⯑liti [...], and proves often mortal in a few H [...] and even the Plague it ſelf. This ex [...]me Heat has ſudden Interruptions of Cold, which makes the Inhabitants ſtill more unhealthy. The Inhabitants, during the Campſin, live under Ground. The Heat, during the Months of June [131] and July, which, by the Courſe of the Sun, ſhould be the greateſt, is ſo mo⯑derated by the Northerly and moiſt Winds blowing over the Mediterranean, and by the Overflowing of the Nile, that the In⯑habitants grow healthy, and ſow their Seed in the Months of September and Oc⯑tober. Their Winter has ſeldom any Snow, Froſt, or Rain, or any thing be⯑ſides Dew; unleſs in ſome Places bor⯑dering upon the Mediterranean, and re⯑ceiving Clouds from thence. So the reign⯑ing Winds in Egypt are the Southerly, blowing as it were from an Oven; and the Northerly moiſt and cold over the Mediterranean; and this laſt perhaps two Thirds of the Year, and during the great⯑eſt Solar Heats. Another Cauſe by which both the Heat and Drought of the Air is temper'd, is the Overflowing of the Nile, which riſing in the Moun⯑tains of Aethiopia, bends its Courſe North⯑erly through a Tract of Land near 30 Degrees. By the Rains falling in thoſe Mountains, the Nile has ever ſince the Memory of Man begun to ſwell the 17th of June, New Style: It riſeth every Day about 8 or 10 Inches, and begins to fall in Auguſt; decreaſeth till May, when it is in a manner ſtagnating. The Li⯑mits of its Height are, from 26 the [132] higheſt of all, to 18 the loweſt, in Cu⯑bits; the middle 24; 18 is a Height barely ſufficient to make an Inundation. Its Water not only refreſheth the Air with a kindly Moiſture, but is the moſt delicious Drink in the World, when purify'd by the Depoſition of its Sedi⯑ment, being of it ſelf a Cure for moſt Diſtempers, where Dilution, a Diureſis or Sweating is neceſſary, which Proſper Alpinus found by Experience. During the time of the Increaſe of the Nile, the Clouds paſs over Egypt, driven by the Northerly Winds, and no doubt fall down in the Mountains, and contribute to moiſten and cool the Air. Proſper Alpinus gives credit to the Experiment of judging of the Increaſe of the Nile, by a Lump of Earth taken out of the River, and kept dry, which begins to increaſe in Weight as the River begins to ſwell; and by the Quantity of this Increaſe, they judge of the Quantity of the Inundation. That the Earth will increaſe by Moiſture is certain; that the Quantity of Moiſture may be a Meaſure for that of the Rain, and that for the Quantity of the Inundation, are all pro⯑bable; but a Spunge perhaps might be a better Hygrometer than the Earth of the River.

[133] VI. There are ſeveral Things remark⯑able in the Conſtitution of the Egyp⯑tian Air. The Perſpiration of the Soil, which is ſandy and barren, cannot affect the Air very much, the Exhalations be⯑ing moſtly either from the Surface of the Inundation, or the Mud and Slime after it is over. The natural Heat and Dryneſs of the Air, and the Change from that to cooler Moiſture; the A⯑batement of the Tropical Heats by Northerly Winds; the Extremity of Heat and Drought, by the Southerly Winds blowing over Sands; and the Moiſture again induced by the Clouds, from the Mediterranean and the Inunda⯑tion; the Exhalations from ſtagnating and putrid Water, when the Inundation is quite over; and laſtly, the Temperance and regular Diet of moſt of the Inhabi⯑tants, muſt give a fair Experiment of the Effects of Air upon Human Conſti⯑tutions. Accordingly, thoſe who labour, live hard, and cannot defend themſelves from the Injuries of the Wind, moſtly dry and hot, are extremely lean and ſqualid: The Rich, by a plentiful and nouriſhing Diet, and preſerving them⯑ſelves from the Heat and Drought by Bathing, Relaxation of their Fibres by [134] drinking the Water of the Nile, are of⯑ten fat.

VII. The Air of Egypt having no noxious Qualities from the Perſpiration of the Ground, were it not from the accidental ones above-mention'd, would be extremely wholſom; and the People who know how to defend themſelves from thoſe Accidents, live to great Ages. The frequent Changes of Heat and Cold, Moiſture and Drought, pro⯑duce all the Diſtempers of the Catar⯑hous Kind, Arthritick Diſeaſes; and, by the ſtrong Perſpiration, Leproſies, e⯑ven the Elephantiaſis. The Effects of a hot dry Air, by a Southerly Wind, blow⯑ing over a ſandy Country, are felt ſtrongly; inflammatory Diſtempers, eſpe⯑cially a raging Fever with a Phrenſy, call'd Demelmuia, mortal in a few Hours. They feel likewiſe all the good Effects of the Abatement of this Heat and Drought by Northerly Winds, the Over⯑flowing of the Nile. They are likewiſe ſubject to all the Diſeaſes from putrid and ſtagnating Water, and Exhalations from Heat after the Inundation is over; and theſe are often peſtilential; therefore ſuch as can, live remote from the Channel of the River.

[135] VIII. Peſtilential Diſtempers are fre⯑quent in Egypt: It is a popular Opi⯑nion there, that they are brought from Syria, Barbary, and Conſtantinople. All I can infer from hence is, that the Plague has ſomething infamous as well as ter⯑rible, and no Country will own it to be their own Product, for the People of Conſtantinople alledge it is imported to them from Egypt: But what I think demonſtrates the Plague to be endemial to Egypt, is its regular Invaſion and going off at certain Seaſons; beginning about September, the time of Subſidence of the Nile, and ending in June, the time of the Inundation; in the firſt Caſe are all the Cauſes productive of Putre⯑faction, Heat, and putrid Exhalations, and no Winter Froſt to check them. But what is wonderful, the Plague and the Fevers, from the Heat of the Camp⯑ſin, go off by the Northerly Winds, and the Overflowing of the Nile. The whol⯑ſom Quality of Northerly Winds for checking peſtilential Diſtempers, has been obſerv'd by all antient Phyſicians; and, to ſhew that the Plague depends upon the Temperature of the Air, Proſper Alpinus takes notice, that upon the Swel⯑ling of the Nile, the Infection, and e⯑ven the Danger from infected Clothes [136] and Furniture, goes off; beſides the cool⯑ing of the Air, the Northerly Winds may diſſipate the ſtagnating Vapours, and the Running of the Nile the ſtag⯑nating Water. Galen and Hippocrates both obſerv'd, that the Elyſian or North⯑erly Winds blowing in Summer, made a wholſom Seaſon. This Obſervation is more ſenſible in hot Countries than in ours.

IX. I thought it worth while to in⯑quire into the Effects of the Air within the Tropick, and particularly in ſome Place under the Line: It happens lucki⯑ly that Boutius, a very learned and ſa⯑gacious Phyſician, has left us a De⯑ſcription of the Air and Diſeaſes of the Inhabitants of Java: Tho' its Situa⯑tion under the Line muſt make it hot, and as therefore ſome would imagine extremely dry, Boutius ſays it is moiſt, from the great Quantities of Rain and ſtagnant Water, and from Moiſture and Heat, and perhaps from Salts produc'd from thoſe Qualities. The putrifying Quality of the Air is very manifeſt in rotting of Clothes, and ruſting of Me⯑tals: From theſe Qualities, the Air feels to Human Bodies, piercing and ac⯑tive. All the Inhabitants of hot Coun⯑tries have that Senſation of the pene⯑trating [137] Quality of Air, cold after great Heats, which perhaps proceeds chiefly from the Pores of their Skin, being re⯑lax'd before by Heat; ſuch Bodies muſt imbibe the outward Air faſter. In Ja⯑va, as in Egypt, the Northerly Winds render the Air wholſom, by abating the extreme Heat; ſome Land Winds carry⯑ing along with them the ſtagnant Va⯑pours, are often otherwiſe. The Soil being fruitful and rich, emits Steams, conſiſting of volatile and active Parts, which fructify the Soil, but are hurtful to Human Bodies. The Seaſons here cannot be diſtinguiſh'd by their Heat, by reaſon of the Smallneſs of their La⯑titude: There are only two; what may be call'd Winter, is the Rainy Sea⯑ſon: This Seaſon is attended with Diſeaſes which depend upon Putrefac⯑tion. The Inhabitants meaſure their Sea⯑ſons of Heat and Cold by the Times of the Day; the Mornings and Nights are cooler by the Abſence of the Sun, and by the Sea Breezes; the ſcorching Heat of the middle of the Day, makes that Time unfit for Buſineſs.

X. The popular Diſeaſes here are, 1ſt. A Species of Palſy, call'd by the In⯑habitants of this and ſome other Coun⯑tries of the Eaſt-Indies, Beriberium; the [138] Cauſe of which is evidently cold Air, imbib'd by the Pores of the Skin, ex⯑tremely relax'd by Heat before, and there⯑fore invades ſuch as incautiouſly expoſe themſelves to the Morning Air, or throw their Bed-clothes off in the Night. Another nervous Diſeaſe, call'd Catalep⯑ſis, is likewiſe popular in this Country, and proceeds from the penetrating Qua⯑lity of the Air imbib'd by relax'd Bo⯑dies. In this Diſeaſe the Patient grows rigid, like a Statue, and dies in a few Hours. Diarrhoeas and Dyſenteries are common from the ſame Cauſe, from ſud⯑den Suppreſſions of Perſpiration; the plentiful Uſe of cold Fruits, from the ſame Cauſes; they invade us in Autumn. It is Matter of Obſervation, that great Heats exalt the Bile, perhaps by the Ex⯑hauſtion of the watery Particles which dilute it by a ſtrong ſenſible Perſpira⯑tion; and therefore the Cholera Morbus, and other Diſeaſes of the Liver, are common and fatal in the Eaſt-Indies; and from diſeaſed Livers, Dropſies are common in Java. Atrophies are like⯑wiſe frequent in Java. In this Coun⯑try then, Fevers are ſeldom intermitting, but continual, with Phrenſies, and other dreadful Symptoms, as during the Camp⯑ſin in Egypt, proving mortal in a ſhort [139] time. The Author deſcribes a Species of Fever in the Iſlands of Solor and Tymon, with very particular Symptoms; if the Fever interrnits, the Patient is ſeiz'd with Convulſions reſembling a [...] viti; the Inhabitants aſcribe this Diſeaſe to the Exhalations of the Santalum Tree. There are likewiſe Spittings of Blood, and Ulcers in the Lungs, in ſuch as expoſe themſelves to the Night Air. The Author takes no⯑tice of Blindneſs as being common in the Coaſts of Amboyna, and the Molucca Iſlands, which the Inhabitants aſcribe to the immoderate Uſe of hot Rice; there⯑fore they expoſe their Rice, after it is boil'd, to the cool Air; perhaps they may be miſtaken likewiſe as to the Cauſe of this.

XI. The Diſeaſes of Fort St. George, tho' it lies in 14 Degrees of Northern Latitude, reſemble very much thoſe a⯑bove deſcrib'd in Java: When the Wind blows from the Weſterly Points, from April to the End of July, it renders the Air ſo hot and dry, that were it not for Sea-Breezes from the South-Eaſt in the Afternoons, the Inhabitants could not bear it: The Effects of this Heat are a denſe thick Blood, inflammatory Diſ⯑eaſes, Fevers with Phrenſies, Cholera Mor⯑bus, [140] Beriberium, the Barbiers, as the Inhabitants call it here, the ſame, and depending upon the ſame Cauſe as that in Java From the Middle of October to the Beginning or Middle of Decem⯑ber, the Wind blows commonly between the North and Eaſt, and is call'd their Monſoon, or Rainy Seaſon: The moſt re⯑markable Diſeaſes of that Seaſon, are obſtinate Diarrhoeas, from the Moiſture and Coolneſs of the Air; and I believe it will be found an Obſervation general⯑ly true, That a wet Seaſon produceth Ca⯑tarrhs or Seroſities of all kinds, likewiſe putrid Fevers, and intermitting Fevers; for during the extreme Heats, the Fevers are continual. The Air is temperate from December to March. The acute Diſea⯑ſes which invade in that Seaſon, eſpe⯑cially the Smallpox, are leſs dange⯑rous than thoſe which invade in a hot⯑ter.

XII. The Effects of Air extremely cold, you will find in the Journals of ſuch as have navigated in great North⯑ern Latitudes, or have wintered in Green⯑land and other Countries; theſe are ta⯑ken notice of N^o XVI. of the Third Chapter, and muſt needs be very diffe⯑rent, and deſtroy Mankind by another Claſs of Symptoms, than thoſe of hot [141] Air. What Joſeph D'Acoſta ſays of the Coldneſs of one Mountain of Peru, ſeems to make it exceed even that of Greenland in Winter, its fatal Effect upon Human Bodies being more ſudden. By a few Obſervations collected in this Chapter, the Reader may eaſily perceive, that upon a general Notion of the Wea⯑ther and Diſeaſes of different Countries, a Piece of Knowledge, almoſt ſcienti⯑fick, might be founded, not incurious or uſeleſs to Mankind.

XIII. There are ſome few modern Phyſicians who have left us Obſerva⯑tions of the Seaſons, and the cotempora⯑ry epidemical Diſeaſes, as Bernardini Ra⯑mazini, a Phyſician of Modena, who has diſtinguiſh'd himſelf by ſeveral ingeni⯑ous Pieces which he has publiſh'd in his Hiſtory of the Conſtitutions of the Years 1690, 1691, 1692, 1693, 1694, and the epidemical Diſeaſes about Mo⯑dena, and the adjacent Countries. There are many things remarkable in the Year 1690. After four or five Years preceed⯑ing of great Drought, attended with great Plenty. There began to fall in the Spring, 1689, great Rains, upon which enſued a moſt deſtructive Mil⯑dew upon the Corn and Legumes; the Rains ſtill increas'd, and continued the [142] Year 1690, with this deſtructive Plague amongſt the Vegetables, which Ramazi⯑ni obſerves to be often ſucceeded with epidemical Diſeaſes amongſt Mankind: The whole Year was cold, cloudy, rainy, attended with a great Inundation of the Po, and other Rivers, the Coun⯑try being all cover'd over with Water. What was obſervable was, the Silence of the Graſhoppers, and Croking of Frogs, and Bees not making Honey: No remarkable Diſeaſes in the Winter, becauſe the Heat had not begun to raiſe the Vapours: A great Run of Inter⯑mitting Fevers in the Spring, which ſtill multiply'd, and ended in double Ter⯑tians in the Summer, which were the moſt epidemical that ever were known, and the Country more unhealthy than the Towns; an unuſual Vermination, or Quantity of Worms in Human Bodies; Parotids, ſuppurating Diarrhoeas, and all other Catarrhous Diſtempers. Theſe Fevers not very mortal, conſidering the vaſt Numbers that were ſeiz'd, except a⯑mongſt Children and tender Women: No continued Fevers: Other Animals ſickly; Cattle, with Eruptions about their Heads. What was ſtill moſt re⯑markable, was the nocturnal Acceſſion of the Fevers, being the worſt, and a [143] great Relaxation or Debility of Patients till the Sun was up, the Fever depend⯑ing upon Acidity rather than Bile; and for that Reaſon the Bark was generally ineffectual, and the copious Uſe of Wine generally beneficial. Ramazini aſſigns probable Cauſes for all thoſe Symptoms: The unuſual Vermination caus'd by In⯑digeſtion of the Eggs of Inſects, which are commonly taken in with Aliment; Sucklings dying, from the Acidity and other bad Qualities of the Nurſes Milk. He reckons the Silence of Graſhoppers a Preſage of a ſickly Time; and quotes Mercurialis, who obſerv'd the ſame thing at Padua, in 1577. The 1691 was directly contrary in its Temperament to the preceeding; a froſty dry Winter, a hot dry Spring, a hot Summer; and as the Seaſons, ſo were the Symptoms of Diſeaſes almoſt oppoſite: The popu⯑lar Diſeaſes of the Winter, were Apo⯑plexies, Quinzies, Pleuriſies, Inflamma⯑tions of the Lungs, Catarrhs, all with ſizy Blood; letting of Blood, and what⯑ever gave Fluxility to it, reliev'd. The Country-people who us'd Labour and Exerciſe, were more healthy than Citi⯑zens. In cold dry Weather, the Inha⯑bitants of the Country and Cities are equally free from the noxious Qualities [144] of the Perſpiration of the Earth; there⯑fore the Advantage as to the other Qua⯑lities of the Air, is on the Country's Side, eſpecially in Diſtempers inflamma⯑tory, becauſe of the leſs Exerciſe, more plentiful and leſs ſimple Diet of Citi⯑zens. In the Spring, ſcabious Irrup⯑tions upon the Skin were epidemi⯑cal; this perhaps from the Acidity of the Blood, contracted the former Year, and the Salts retain'd beginning now to perſpire by Heat. Madneſs amongſt the Dogs was epidemical from great Heat and Drought. A prodigious Number of Fevers of the bilious kind in the Sum⯑mer, which turn'd mortal in the Au⯑tumn; the Remedies of which were di⯑rectly oppoſite to thoſe of the Fevers of the preceding Year; for theſe want⯑ed Cordials, and as it were a Spur; but thoſe of the Year 1691 wanted a Bridle, and were generally reliev'd by Blood-letting, cooling acid Medicines, all the Symptoms proceeding from a bilious Acrimony: The Bark, which had been ineffectual in the Intermittents of the former Year, was ſucceſsful in this. Ramazini obſerves in the ſucceeding Years 1692, 1693, 1694, tho' diſſimu⯑lar in their Temperature, yet were not very unlike in their epidemical Diſeaſes, [145] but eſpecially in a petechial or ſpotted Fever, which raged moſt at the New and Full Moon; he aſcribes this to an unuſual Duration of Southerly Winds, which has been obſerved by all Phyſi⯑cians to make an unwholſom Conſtitu⯑tion of Air; he aſcribes it to this Cauſe, becauſe the Inhabitants of the Foot of the Appennines being defended from the Southerly Winds, were not infeſted with theſe petechial Fevers. I think I may venture to add one Reflexion to thoſe of the judicious Author, That if the great Rains and Moiſture of the Year 1690, had been ſucceeded with great Heat, the Fevers would have put on ano⯑ther Genius, and perhaps been Peſtilen⯑tial.

XIV. There is alſo publiſh'd the Epi⯑demical Hiſtory of Germany, by ſeveral eminent Phyſicians, in which the Rea⯑der will find many things remarkable, which it would be too tedious to in⯑ſert, but from which we ſhall draw ſome Obſervations in the laſt Chapter. Our learned Preſident, Sir Hans Sloan, has given us a Journal of the Wea⯑ther of Jamaica, and the Hiſtory of the popular Diſeaſes of that Country; the Reſemblance of the Conſtitution and Diet of the Inhabitants to thoſe of [146] their Mother-Country, occaſion a great Affinity likewiſe in the popular Diſeaſes, except in ſome few Caſes which are the Product of a warmer Climate. But as there is ſtill a great Penury of ſuch Obſervations, all we can do is to rea⯑ſon from the Laws of Mechanicks, and the known Properties and Qualities of Air, what muſt be their natural Ef⯑fects. It ſeems agreeable to Reaſon and Experience, that the Air operates ſenſi⯑bly in forming the Conſtitutions of Mankind, the Specialities of Features, Complexion, Temper, and conſequently the Manners of Mankind, which are found to vary much in different Coun⯑tries and Climates. As to Features, what an infinite Variety ariſeth from the Combination of the Parts of a Human Face, ſo that ſince the Creation of the World, perhaps there were never two that, upon a narrow Inſpection, perfectly reſembled one another. There are Faces not only individual, but gen⯑tilitious and national; European, Aſia⯑tick, Chineſe, African, Grecian Faces, are characteris'd. This Diverſity of Na⯑tional Features and Shapes is not alto⯑gether the Effect of Propagation from the ſame original Stock; for it is known by Experience, that Tranſplantation [147] changeth the Stature and outward Shape, both of Plants and Animals. Hippocra⯑tes makes great Account of the Influ⯑ence of the Air upon the Foetus, both before and after Birth: He is of Opi⯑nion, that the great Variety of Euro⯑pean Faces is owing to that of the Air and Seaſons; there being ſuch great Ex⯑curſions in the Extremities of Heat and Cold, their Offspring is at it were be⯑got and brought forth in different Cli⯑mates. That the Shape of Animals ſhould be modify'd by the Air, is no ways unaccountable: An Animal grow⯑ing, expands its Fibres in the Air as a Fluid, which, by a gentle Preſſure, re⯑ſiſts the Motion of the Heart in the Expanſion and Elongation of the Fibres; and tho' the Fibres of ſeveral Animals ſhoot, as it were, in this Fluid, accord⯑ing to their original Shapes, yet ſuch a Fluid reſiſting by its Preſſure, is, in re⯑ſpect to the Animal, like a ſoft Mold, in which the Body is form'd; and therefore, according to the Quantity of its Preſſure, depending upon its moſt permanent State of denſe, rare, hot, cold, dry, moiſt, muſt have ſome In⯑fluence in forming the outward Figure of ſuch a Body in a State of Accretion: Beſides this outward Preſſure, the Air [148] being mix'd with the animal Fluids, determines their Condition as to Rari⯑ty, Denſity, Viſcoſity, Tenuity, and ſe⯑veral other Qualities.

XVI. That the Complexion depends much upon the Air, is plain from Ex⯑perience; the Complexion of the In⯑habitants of ſeveral Countries being fair, ſwarthy, black, and aduſt, according to the Degrees of Heat, Drought, Moi⯑ſture, or Coolneſs of the Air. The In⯑habitants of Countries in great Lati⯑tudes are generally fairer than thoſe that live nearer the Sun.

XVII. That the Temper and Paſ⯑ſions are influenc'd by the Air, is no leſs certain: People of delicate Nerves and moveable Spirits are often joyful, ſullen, ſprightly, dejected, hopeful, de⯑ſpairing, according to the Weather; and theſe Changes happen, but paſs unob⯑ſerv'd in ſtronger Conſtitutions. There are Days in which the intellectual Fa⯑culties of Memory, Imagination, Judg⯑ment, are more vigorous, therefore it ſeems probable that the Genius of Na⯑tions depends upon that of their Air. Arts and Sciences have hardly ever ap⯑peared in very great or very ſmall Lati⯑tudes: The Inhabitants of ſome Coun⯑tries ſucceed beſt in thoſe Arts which [149] require Induſtry and great Application of Mind: Others in ſuch as require Ima⯑gination; from hence ſome Countries produce better Mathematicians, Philoſo⯑phers, and Mechanicks; others better Painters, Statuaries, Architects, and Po⯑ets, which, beſides the Rules of Art, demand Imagination. It ſeems to me, that Labour is more tolerable to the Inhabitants of colder Climates, and Livelineſs of Imagination to thoſe of hot.

XVIII. There are two things com⯑mon to all Mankind, Air and Aliment; both indeed differ very much in their Qualities, in different Countries and Climates; but thoſe of the Air are per⯑haps more different than thoſe of the Aliment. In peruſing the Accounts of the Temper and Genius of the Inhabi⯑tants of different Countries, we diſcover in them a great Uniformity, even tho' the Race has been chang'd. The Tem⯑per of the Gauls, deſcrib'd by Caeſar and other Writers, is much the ſame with that of the preſent French: There is a remarkable Inſtance of this in the Mi⯑ſopogon of the Emperor Julian; if I rightly remember, he tells us that he had paſs'd a Winter at Paris, where there were more Comedians, Dancers, [150] and Fidlers, than there were Citizens beſides; and I believe if a Race of Laplanders were tranſplanted thither, in a few Years they would be found in the Condition deſcrib'd by the Emperor Ju⯑lian. How is the rugged Temper of the Northern Nation mellow'd by the ſofter Air of the Countries which they conquer'd? Governments ſtamp the Manners, but cannot change the Genius and Temper of the Inhabitants; and as far as they are unreſtrain'd by Laws, their Paſſions, and conſequently their National Virtues and Vices will bear ſome Conformity with the Temperature of the Air. The Inhabitants of Cio are deſcrib'd by the ancient Greeks as looſe and diſſolute, and voluptuous, and ſo they are at preſent; ſome modern Tra⯑vellers affirm, that there is a Softneſs in their Air that diſpoſeth to a ſort of Indolence and Mirth. Nations, as well as Individuals, have their Conſtitutional Vices; and I think there is no ſtronger Proof of the Force of Chriſtian Mo⯑rality, than the Reformation it pro⯑duc'd in National Vices in primitive Times, when it was believ'd and practis'd in its Perfection.

XIX. If we conſider the Cauſes aſ⯑ſign'd by Hippocrates, of the different [151] Temper of the Inhabitants of different Climates, we ſhall find them ſufficient⯑ly proportion'd to their Effects. In Northern Countries, where the Altera⯑tions of the Height of the Barometer, and conſequently of the Weight of the Air, are frequent and great, the Fibres of Human Bodies are in a continual oſcillatory Motion, from a Preſſure of 1200, 1800, yea 3600 more at one time than another; and tho' this, by the Softneſs and Rarity of the Fluid, is in⯑ſenſible, and not dolorifick, it is a ſort of Exerciſe which the Inhabitants of Countries where the Variation of the Height of the Mercury is ſmall or no⯑thing. By the Difference of the Tenſion of the Fibres, the whole nervous Sy⯑ſtem, and the animal Spirits, are in ſome meaſure affected. Let us again conſider the Extremes of Heat and Cold in great Latitudes, operating after the ſame manner, relaxing and conſtring⯑ing the Fibers by turns, and the extreme Cold acting likewiſe as a Stimulus, in conſequence of which we find an Acti⯑vity and Tolerance of Motion and La⯑bour, in dry froſty Weather, more than in hot; whereas the People within the Tropicks are conſtantly in the State of our hotteſt Weather. Whoever conſiders [152] Mankind in ſuch different Circum⯑ſtances, will find that the Temper, both of their Body and Mind, muſt be dif⯑ferent, and that a greater Variety in the oſcillatory Motion of the Fibres of Northern People muſt produce the ſame in their Spirits, and therefore a propor⯑tional Inequality in their Paſſions, and conſequently greater Activity and Cou⯑rage. That the Inhabitants of Climates, where the Difference of the Weight, Heat, and Cold of the Air is but ſmall, feel only the Changes of the Tenſion of their Fibres, proceeding from Drought and Moiſture, being free from the Agi⯑tations and uneaſy Senſations of North⯑ern People, proceeding from the Cauſes above enumerated; and the Motions of their Fibres and Spirits being more uni⯑form, they may be for that Reaſon, and from exceſſive Heats, lazy and in⯑dolent: From Inactivity and Indolence there will follow naturally a flaviſh Diſ⯑poſition, or an Averſion to contend with ſuch as have got the Maſtery of them. Hippocrates tells us, that the Eu⯑ropeans owe their Courage to the Varie⯑ty and Coldneſs of their Climate, and their Laws which ſecure their Proper⯑ty to their Courage. Thus far I have ventur'd to explain the Philoſophy of this [153] ſagacious old Man, by mechanical Cauſes ariſing from the Properties and Quali⯑ties of the Air; to which I ſhall add another, ſomewhat foreign to my Sub⯑ject: That in Countries which do not produce without much Labour, the Land-holder muſt have Aſſurance of the Neceſſaries for his Culture, as his Seed, Granary, domicile Working-tools, &c. This muſt create ſome Property, and where there is Property, there muſt be Laws to ſecure it: From which I beg leave to draw one Corollary; That de⯑ſpotick Governments, tho' deſtructive of Mankind in general, are moſt improper in cold Climates; for where great Labour is neceſſary, the Workman ought to have a certain Title to the Fruits of it. There are Degrees of Slavery, and, generally ſpeaking, it is moſt extreme in ſome hot and fruitful Countries.

XX. I will venture to add another Obſervation, which, tho' it may ſeem a little too much refin'd, is not improba⯑ble: That the Air has an Influence in forming the Languages of Mankind: The ſerrated cloſe way of Speaking of Northern Nations, may be owing to their Reluctance to open their Mouth wide in cold Air, which muſt make their Language abound in Conſonants; [154] whereas from a contrary Cauſe, the In⯑habitants of warmer Climates open⯑ing their Mouths, muſt form a ſofter Language, abounding in Vowels. Ano⯑ther Obſervation is, That People in windy Countries naturally ſpeak loud, to make themſelves be heard in the open Air.

XXI. That the Conſtitutions of Man⯑kind differ according to the Qualities of the Air in which they live, is an un⯑conteſted Matter of Fact, and depends upon obvious Cauſes. Hippocrates ob⯑ſerv'd, That the Inhabitants of moiſt Countries were bloated, leucophlegma⯑tick, and dull, from the Relaxation of their Fibres, and the Moiſture imbib'd with the Air; and contrary Cauſes muſt produce contrary Effects: Heat indeed relaxeth the Fibres, but by abſorbing the Moiſture may likewiſe harden, and ren⯑der them more ſolid. The Bones of Animals in hot Countries are more ſo⯑lid, and ſpecifically heavier, than of thoſe in cold Climates, as may be ſeen in comparing the Bones of the Limbs of African Horſes, and thoſe of North⯑ern Countries. The Blood too, in hot Countries, is thicker and blacker by the Diſſipation of the ſerous Part, by ſenſi⯑ble Perſpiration: This is Matter of Fact, [155] atteſted by Phyſicians who have practi⯑ſed in thoſe hot Countries. From this black aduſt State of their Blood, they are atrabilarious. Great Heats exalt the Bile, by diſſipating the Moiſture which dilutes it. Bile, of it ſelf, is the moſt unperſpirable of Animal Fluids; it ſtops at the Surface of the Skin, and diſco⯑lours it. The Animal Juices, in hot Countries, are more exalted; this is true in venomous Creatures. There is ſome Analogy between Plants and Animals, and both are longer in coming to Ma⯑turity in cold and moiſt Air. The pro⯑lifick Age of Mankind is much earlier in hot than cold Countries, the Fe⯑males being in that State at Ten Years of Age. The Inhabitants of warm Countries are not ſubject to be fat, for a ſtrong Perſpiration keeps an Animal from being ſo. A copious Diet and Inactivity will always occaſion Excep⯑tions from the general Rule.

XXII. Cold and moiſt Air muſt ne⯑ceſſarily produce phlegmatick and lax Conſtitutions, and by ſtopping Perſpira⯑tion with a copious Diet, accumulate the Animal Oil. Dry and cold Air in a Degree tolerable to Human Bodies, which is the State of our Winter Froſts, creates a ſtrict Conſtitution of the Fi⯑bres, [156] and all the Effects thereon depend⯑ing, Vigour and Activity.

XXIII. As to different Heights and Regions of the Air, it ſeems probable that the Conſtitutions of Miners and Mountaineers muſt differ conſiderably; and I wiſh the Differences were well obſerv'd. Mountaineers, by having a leſs Preſſure of Air upon them, muſt exert a greater Degree of Muſcular Strength, like Birds who move in a ra⯑rer Element, and by ſteep Aſcents and Deſcents a greater Variety and Force in progreſſive Motion. The Coldneſs of their Air in ſome meaſure balanceth the deficient Preſſure by Weight. Theſe Cauſes naturally produce Strength and Activity; and even the Pride and Fe⯑rocity aſcrib'd to them by Hippocrates. As Air has a great Influence upon the Fluids and Solids of Human Bodies, it will ſtamp and form them according to its moſt permanent State, during the Cycle or Period of the Seaſon in that Region of the Earth. But leaving this Matter to be further purſued when there are more Data from Natural Hiſtory to proceed upon, I ſhall make a few Ob⯑ſervations upon the Qualities of the Air, as far as they are Noſopoetick, that is, have a Power of producing Diſeaſes.

[157] XXIV. Popular Diſeaſes depend up⯑on what is common to all the People; theſe are chiefly Air and Aliment; it is eaſy to diſtinguiſh the Effects of both. The genuine Effects of Air in produ⯑cing Diſeaſes is beſt diſcover'd in People who live on wholſom Aliment, and are temperate.

XXV. Acute popular Diſeaſes are commonly the Effects of the Tempe⯑rature of the Air; they often invade at ſtated Seaſons of the Year; their Rife⯑neſs, Duration, different Symptoms and Periods, ſeem to depend upon the Al⯑terations of the Weather, and the State of the Air preceding and conſequent up⯑on theſe Alterations. I think this may be inferr'd from the great Uniformity that is obſerv'd in the Symptoms of the Epidemical Diſeaſes of the ſame Seaſon. I believe no body doubts that the late Diſtemper which affected all Europe, was the pure and genuine Effect of the State of the Air. A Perſon in perfect Health going into a Place infected with an epidemical Diſeaſe, ſhall be ſeiz'd with it without any other Error in his Diet, and even without Suſpicion of In⯑fection.

XXVI. As the Force of Human Bo⯑dies is limited, they are not capable to [158] bear Extremities of any kind, of too great Rarity, Denſity, Heat, Cold, Moi⯑ſture, Drought in the Air. From the ſame Cauſe Human Bodies do not ea⯑ſily ſuſtain violent and ſudden Changes which agitate the Fluids and Solids too much; for as the State of our Fluids and Solids change with the Air, violent Alterations in the latter produce the ſame in the former; therefore variable Weather is commonly productive of Diſeaſes; for Example: Suppoſe ſuch a State of the Air as maketh a great Stricture of all the external Parts of the Body, and conſequently an Abate⯑ment of the Circulation in the Veſſels expoſed to the Air, and in thoſe which immediately communicate with them: Suppoſe again the Air is ſuddenly chang'd from this State to one which violently relaxeth the Fibres, by their Relaxation, it is poſſible that the Veſſels which were deſtin'd before to carry the Serum, or Lymph, may admit the Blood, which is an inflammatory State: Accordingly we find that inflammatory Diſtempers of ſeveral kinds are rife in moiſt and warm Weather, preceded by hard and laſting Froſts: Froſt ſtops the Perſpi⯑ration of the Earth, which being reſtor'd by Thaw, fills the Air with an unu⯑ſual [159] Quantity of Vapours, which affect Human Bodies, not only by Relaxation, but as they imbibe them with the Air.

XXVII. The Weather and Diſeaſes of Countries have a good deal of Uni⯑formity; but the unuſual Exceſſes of Heat, Cold, Moiſture, and Drought, produce either a greater Plenty, or un⯑uſual Symptoms in Diſeaſes; and operate more ſtrongly, if the Alterations are ſud⯑den and extreme.

XXVIII. By the Doctrine and Obſer⯑vations of Chap. III. it is plain that Human Bodies cannot long ſuſtain Heat approaching to their natural Heat, far leſs that exceeding it. An Animal dies of an Inflammatory Diſtemper with all the Symptoms of Putrefaction in a Su⯑gar-Baker's Drying-Room. There are ſome Countries in which, during their greateſt Heats, Wax will melt; Man⯑kind, without ſome Defences by Art, cannot bear ſuch an Air. The Symp⯑toms which one feels in extremely hot Weather are feveriſh, a Pulſe quicker than natural, profuſe Sweats, great Thirſt, Debility, Dejection of Appetite; by great Sweats the Blood is render'd denſe; by Debility the Force of the Heart itſelf is diminiſh'd; and indeed by the Conti⯑nuance of the Heat, the whole Body in [160] time may be render'd dry and ſqualid; add to this, ſudden Refrigeration by cool Air, ſo deſirable to Mankind in ſuch a State, for the ſake of which they often incautiouſly expoſe themſelves: I ſay it is very accountable how ſuch a Conſti⯑tution of the Air may work as a Sti⯑mulus, and produce dangerous continued Fevers; and that Catarrhs, and Diſeaſes depending upon Defluxions of Seroſity upon any Part of the Body, in Coughs, Rheumatiſms, Gouts, Diarrhoeas, ſhould in ſuch a Conſtitution much abound, both by Suppreſſion of Perſpiration, and by a ſudden Admiſſion, imbibing of this Seroſity by all the Pores of the Skin, of cool Air, and then he may undergo all thoſe Symptoms in a greater Degree; accordingly, hot Days, with cool Nights, are commonly productive of Diarrhoeas, ſuch is our Weather in the Autumn.

XXIX. Heat, (as was obſerv'd Numb. XIX. of this Chapter) naturally exalts the Bile; therefore bilious Fevers, and Cholera Morbus, may be the natural Product of ſuch a hot Conſtitution of Air.

XXX. Cold both congeals the Fluids and conſtringeth the Solids. It acts like a ſmall Ligature upon the Veſſels, by which the Circulation through the Veſ⯑ſels [161] is retarded; the natural Effect of which is a greater Secretion of Seroſity through the Glands contiguous, for the Extremities of the Veſſels near the Glands being preſs'd, they cannot ſo plentifully carry off the refluent Fluid, by which there muſt be a greater Flux of Liquor towards the Glands, and a greater conſequently from its Emuncto⯑ries; therefore Catarrhs, or ſerous De⯑fluxions upon all the Parts of the Body, but eſpecially from the Glands of the Head and Throat, are a natural Effect of Cold.

XXXI. Obſtructions by Cold in the outward Parts of the Body, drive the Blood preſſing with a greater Force upon the inward Parts, and increaſe Heat. Sizy Blood may be another Ef⯑fect of Cold; this is extremely well il⯑luſtrated by the ingenious Dr. Thomas Simſon Chandos, Profeſſor of Phyſick in the Univerſity of St. Andrew, who has explain'd the Effects of Cold up⯑on the Humours very clearly, by a plain Experiment ſhewing that Blood, after a ſtrong Ligature upon any Joint, will be ſizy upon the letting it out of the Vein with a free Stream; and the Pro⯑feſſor reaſons very juſtly, if the white. Chyle is made red by the Force of [162] Motion, by the Retardation of this Cir⯑culation, in ſome Parts the Blood may grow white, and crude again: Cold is a ſmall ſort of Ligature upon the Veſ⯑ſel affected with it, conſtringing the Veſſel.

XXXII. It was obſerv'd, N^o XXII. Chap. III. That theſe Qualities of the Air act either by the Sums or their Differences, as they conſpire in the ſame Effect, or act oppoſitely. Thus Heat and Moiſture both relax; but if the Air is cold with Moiſture, in that Caſe the Veſſels may be conſtringed, and ſuch a Conſtitution may produce all the Effects of Cold. Water relaxeth all Fibres, Vegetable and Animal; yet a cold Bath conſtringeth the Fibres for a while; any moiſt Steam relaxeth in Proportion to its Heat; beſides, Water may obſtruct as well as relax.

XXXIII. The more pliant the Veſ⯑ſels are, as in tender and young Peo⯑ple, they are more ſenſible of Impreſ⯑ſions by the outward Air; they have a greater Play in the Degrees of Ten⯑ſion than the Veſſels of old People; therefore the Qualities of the Air in conſtringing and relaxing the Fibres pro⯑duce greater Effects upon them; the longer Animal Fibres are kept in any [163] State, the more they loſe their Power of reſtoring themſelves: Therefore the moſt permanent State of the Air of any Country may produce endemial chroni⯑cal Diſeaſes.

XXXIV. Cold is capable of produ⯑cing all the Diſeaſes which depend up⯑on too great a Stricture of the Fibres, and by diminiſhing the Quantity of Perſpiration, either increaſeth that of the other Secretions, or produceth a greater Fulneſs and inward Heat. The Summer Perſpiration being near double of that of Winter, the Appetite, and con⯑ſequently the Aliment, not diminiſh'd, may induce all the Symptoms of a Plethora, if the other Secretions are not proportionally increas'd.

XXXV. Cold, by ſuppreſſing the Per⯑ſpiration of Salts in the Blood, by con⯑gealing the Blood, and likewiſe by a dolorifick Stimulus corroding the Skin, is apt to produce Scurvies and other cutaneous Irruptions, and in Extremity is capable of freezing the Fluids, and re⯑ducing Animal Subſtances to a gangrenous State.

XXXVI. Cold Air is capable of ma⯑king inflammatory Diſtempers with cu⯑taneous Irruptions more dangerous, by hindering the Relaxation of the Skin. [164] I believe it will be found that the Small-pox is moſt fatal during hard Froſts, and cold North-Eaſterly Winds. I re⯑member that the Small-pox which were exceeding mortal during ſuch a Seaſon, grew more favourable by the Tepor and Moiſture in April and May. The artificial Qualities produc'd in the Air of the Patient's Room, are not ſuffi⯑cient to balance its natural State.

XXXVII. Cold Air, by its immedi⯑ate Contact with the Surface of the Lungs, is capable of abating or ſtop⯑ping the Circulation of the Blood, and bringing them into an inflammatory State, and by producing Catarrhs and Coughs, is productive of all the Effects of ſuch Defluxions upon the Lungs, Ul⯑cerations, and all ſorts of pulmonick Con⯑ſumptions.

XXXVIII. As to Moiſture and Drought, the Exceſſes of them moſt neceſſarily bring Human Bodies into a morbid State, becauſe they are incapable of bearing theſe Extremes. There is a certain De⯑gree of Humidity neceſſary to relax the outward Parts of the Body, to preſerve the Pores of the Skin in their due Sy⯑metry; the ſame due Degree of Humi⯑dity is perhaps neceſſary to be abſorb'd with the Air, by the Pores of the Skin.

[165] XXXIX. Long Droughts have been found moſt dangerous of all to Human Bodies. The Year 1708, the coldeſt Winter that perhaps was ever felt in England, was not attended with any great Mortality amongſt Mankind. The Year following, 1709, was the wetteſt that was ever known, there having fall'n about 26½ Inches of Rain in Eſ⯑ſex, yet there were no extraordinary Diſ⯑eaſes nor Mortality that Year; the Year ſucceeding, indeed the Small-pox were rife and mortal. The Year 1714 was the drieſt Year that has been yet obſerv'd, there having fall'n that Year in Eſſex not much above 11 Inches of Rain; ſo that the Difference as to Moi⯑ſture, between 1709 and 1714, was a⯑bove Half, and their Proportion as 53 to 24; the Bills of Mortality in London, in 1714, increas'd 5512, and the Mor⯑tality begun that Year amongſt the Cattle. There has been an unuſual Drought for theſe two Years paſt, for I think the beſt Eſtimation of the Dry⯑neſs of the Surface of the Earth, muſt be taken from the Falling of the Springs, the Conſequence of which has been un⯑uſual Diſeaſes amongſt ſeveral Animals, and a great Mortality amongſt Mankind. It is true, this did not happen during [166] the dry Weather; the ſudden Alteration, as well as the preceding State, might operate, the Surface of the Earth being by the Drought firſt ſhut up, and af⯑terwards opened by the Rain, might af⯑fect Human Bodies variouſly, as in warm Weather, and Thaws after great Froſts.

XL. Moiſture relaxeth, unleſs it be combin'd with a greater Degree of Cold, which ſubducts ſo much of its relaxing Quality. The Inhabitants of cold and moiſt Countries are leucophlegmatick, bloated, and have all the Symptoms of Relaxation; therefore Effects of ſuch a State of Air are all the Diſeaſes which the Methodiſts claſs under the Title of the Laxum. If Air is imbib'd by Hu⯑man Bodies, the watery Parts, and per⯑haps theſe chiefly, enter; and catarrhous Diſtempers ſeem to depend upon the Moiſture, as well as the Coldneſs of the Air. The leaſt Moiſture taken in by the Windpipe, immediately is reject⯑ed by Coughing. It is not merely the Suppreſſion of Perſpiration by Cold or Moiſture, that is the Cauſe of the Coughs and Defluxions upon the Breaſt, by in⯑ducing a Plethora, and a proportional one in the Glands; but the moiſt Air is really imbib'd, and affects the Glands by [167] immediate Contact, or as a Stimulus. It appears by the Journals of Perſpira⯑tion, that Coughs and Colds have often invaded, where there was no Suppreſ⯑ſion of Perſpiration, and that a Sup⯑preſſion of Perſpiration is not always attended with a Cough or a Cold. Moi⯑ſture imbib'd with the Air, after Relax⯑ation of the Pores of the Skin, may affect all the glandulous Parts of the Body, even thoſe of the Guts, produ⯑cing Diarrhoeas. I know it to be true by Experience, that moiſt Air is pro⯑ductive of nephritick Colicks, in ſuch as are ſubject to them. However, I propoſe this as a Probability, which by future Obſervations and Experiments may be better cleared.

XLI. Hot and moiſt Air producing Relaxations, and conſequently an Abate⯑ment of the Force of the Solids in pro⯑pelling the Fluids muſt produce Stagna⯑tion, Tumors, and Putrefaction in the Liquids, and all the other Diſeaſes de⯑pending upon a lax State of Fibres: Hippocrates obſerv'd ſuch Diſeaſes al⯑ways conſequent upon a moiſt Conſti⯑tution of Air, with Southerly Winds, which are warm; and I have obſerv'd the ſame in this Country. As Perſpira⯑tion is the laſt Action of perfect Animal [168] Digeſtion, that Conſtitution of Air which ſuppreſſeth Perſpiration muſt hin⯑der Digeſtion; therefore cold and moiſt Air muſt be hurtful to Stomachicks. Ca⯑tarrhs and Coughs are the Effect of cold and moiſt Air, and thoſe habitually af⯑fecting the Lungs may produce pulmo⯑nick Conſumptions; yet it ſeems proba⯑ble, that where thoſe Conſumptions are a popular Diſeaſe, they proceed from ſome particular Acrimony in the Air of that Country, affecting that tender Or⯑gan by immediate Contact, and perhaps all the Glands of the Body, for our Conſumptions are ſcrophulous. Scro⯑phulous Diſtempers are very common in this Country. If the Air be charg'd with any ſaline acid Particles, they will naturally coagulate the Fluid where they touch. From the Abundance of Mine⯑ral Waters of all ſorts in England, it may be inferr'd, that there are abundance of Mineral Steams.

XLII. The Chirurgeons prove the Ef⯑fects of Air in their Profeſſion, even more than the Phyſicians; for when the Fi⯑bres of Human Bodies gape, by a Wound or Sore, the outward Air has an im⯑mediate Acceſs to the open Veſſels, and affects the Fluids in them by immediate Contact, and affects a wounded Part as [169] it were raw Fleſh: The Healing of this Wound, or the Union of its Parts, is perform'd by the Elongation of the Fibres, and that depends both upon the State of the influent Fluid and its vaſ⯑cular Fibres, as to Flexibility, Rigidity, Strength, or Degrees of Reſiſtance; and thoſe depend very much upon the Air, which is in immediate Contact: For Example, A Wound in cold froſty Wea⯑ther muſt gape more, becauſe the Cold contracts the Fibres more than tepid Weather, therefore in the latter the Fi⯑bres muſt be more pliant and flexible; ſuch a Conſtitution of the Air as would naturally putrify raw Fleſh, muſt en⯑danger by a Mortification. Defences by Emplaſtick Applications are not ſuffi⯑cient to defend a Wound or Sore from being affected with the Air which touch⯑eth it; therefore Chirurgeons are ſome⯑what nice in the Choice of the Seaſons in which they perform certain Opera⯑tions. From the Qualities of the Air it happens that Wounds in different Parts of the Body are ſome eaſier, ſome harder to be cur'd in different Countries. An eminent Chirurgeon of our Army, du⯑ring the laſt War with France, was pleas'd to tell me two very remarkable Things relating to this Subject: One [170] was, That after the Battle of Hochſted, the Wounded in the Hoſpital of Nor⯑lingen in Germany, fell all into adema⯑tous Swellings, of which many miſcar⯑ried; that after they were remov'd into another Air, this Symptom went off. Another Obſervation was, That at the Siege of Liſle, there was a great Diſpoſition in every Wound to turn gangrenous, eſpe⯑cially thoſe of the Head, ſo that few re⯑cover'd of thoſe that were trepan'd. This he obſerv'd to be peculiar either to that Seaſon, or to that Place. In the Hoſpitals at Paris, Wounds in the Head are much diſpos'd to Gangrenes.

XLIII. From what has been ſaid on the Subject of the Effects of the Air on Human Bodies, it is plain that no vi⯑tious State, either of the Solids or Flu⯑ids, but is producible by the common Properties and Qualities of Air, and their Changes and Combinations. By the Qualities of Air the ſolid Parts may be ſtimulated: For Example, The Sti⯑mulus of extreme Cold is very ſenſible: Heat, or any Quality of Air ſo exceſſive as to produce a dolorifick Senſation, acts as a Stimulus: What obſtructs the Paſſages of the Veſſels which communi⯑cate with the Air, is ſtimulating, by in⯑creaſing the Force of the Heart and the [171] Fibres to overcome the Obſtruction; this either Cold or Moiſture may do, which often produce, firſt Chilneſs, and then a ſucceeding Heat, which are fe⯑veriſh Symptoms: Many volatile Parti⯑cles floating in the Air, as the odorife⯑rous of Vegetables, act as a Stimulus, and we find can produce Headaches: That the Fibres are conſtringed and relaxed by the Alternations of the Properties and Qualities of the Air we have already de⯑monſtrated: That the Fluids may be vi⯑tiated in the ſame manner, is no leſs plain: That the Blood may be condenſed by Heat, by abſorbing the moſt fluid Part: That a certain Degree of Heat will attenuate, and a greater coagulate the Se⯑rum; and Heat in general is capable of producing great Acrimony and putrid Fevers of all ſorts, is true from Expe⯑rience, and any Degree of Heat greater than that of a Human Body will do ſo; for our natural Heat is near the Degree of Coagulation. Cold likewiſe condenſeth the Fluids in immediate Contact with it. Cold is capable of producing Sizeneſs and Viſcoſity in the Blood. By the ſame Cauſes, Acrimony of all ſorts, to the Degree of Putrefaction, is producible by Air. Evacuations of all ſorts, from all the glandulous Parts of the Body, are [172] producible by the Stoppage of Perſpira⯑tion: For Example, There is no diure⯑tick Medicine which works ſo ſtrong in a Flux of Urine, as a Suppreſſion of perſpirable Matter in Hyſterical Caſes. Cold promotes all Catarrhs, Coughs; and moiſt Air, Diarrhoeas, and copious Se⯑cretions from the Glands of the Guts; without which Evacuations, Stoppage of Perſpiration produceth a Plethora or Ac⯑cumulation of the Humours in the Veſ⯑ſels. From theſe Conſiderations it ap⯑pears that the Diſeaſes, eſpecially the a⯑cute of any Seaſon, chiefly depend upon the Conſtitution of the Air, by which they are modify'd, as to their Rifeneſs, Duration, Degrees of Danger, their par⯑ticular Symptoms, Circulations and Pe⯑riods: In which we muſt not only con⯑ſider the preſent, but the preceding State of the Air, becauſe, as they are more ſi⯑milar or contrary, the Alterations pro⯑duc'd in Human Bodies, are leſs or more violent; particularly, I believe it will be found that ſudden Changes from the Ex⯑tremes of Cold and Dry to Heat and Moiſture, are Cauſes which operate ſtrongly in modifying the Diſeaſes of that Seaſon: That long and exceſſive Heats, by inducing Debility, are apt to ſtamp the ſucceeding Fevers with nervous Symp⯑toms: [173] That ſuch a dry Conſtitution of Air as is apt to curb the Skin, and ob⯑ſtruct its Pores, makes the Criſis by Sweating more difficult; perhaps the different Periods of Fevers, Quotidian, Tertian, Quartan, may depend upon a preceding greater Viſcoſity, or Obſtruc⯑tion in the Veſſels, produc'd by the Con⯑ſtitution of the Air: That the more dangerous State of Small-pox, and other inflammatory cutaneous Irruptions, de⯑pends upon the Air, I think, ſeems very plain, as it induceth a greater Laxity or Stricture of the Fibres, or creates a greater Obſtruction in the Veſſels of the Skin: That Diſeaſes of the Lungs, as far as they are not the Product of bad Diet, depend chiefly upon the Qua⯑lities of the Air, ſeems evident; the Lungs are expos'd to the outward Air, which has an immediate Admiſſion in⯑to the Air-bladders, and perhaps into the Blood-Veſſels; and whatever Effect the Air has upon the Skin, this muſt be expected upon the Lungs in a par⯑ticular manner. It is needleſs to enu⯑merate many Particulars, which the Reader may eaſily collect from the Chap⯑ter that treats of Reſpiration.

XLIV. I have hitherto conſider'd on⯑ly the common Properties and Qualities [174] of the Air which are ſenſible, and ſhewn that they are productive of all the Symptoms of Diſeaſes, and for which there is no Occaſion to have Recourſe to its Qualities, occult or extraordinary, which probably it is often endued with; For beſides the Qualities of hot, cold, moiſt, dry, the Air may be ſaline, oily, both which Qualities it diſcovers ſome⯑times by its Effects on Bodies; beſides, from the Action of the heterogeneous Bodies contain'd in it, ſome new Sub⯑ſtances may be produc'd of a Nature different from the Ingredients. The ſaline Exhalations from the Earth may be different at different times; ſuch Salts exhal'd at particular times from the Earth, may enter Human Bodies, and operate like Poiſons, and ſuddenly infect the whole Maſs of Blood, as the Venom of a poiſonous Animal, or as other Sub⯑ſtances injected into the Blood-Veſſels, which produce immediately mortal Symp⯑toms; or they may operate more ſlowly, and produce unuſual Diſeaſes. This is not an impoſſible nor improbable Suppo⯑ſition; yet there is no Neceſſity always to have Recourſe to it, there being no Change in Human Bodies known, but is producible by the Contents, Proper⯑ties, and Qualities, which we are ſure [175] the Air is endued with, and eſpecially by their great Enormities and ſudden Suc⯑ceſſions and Alternations; to ſuch occult Qualities in the Air, many have aſcrib'd Plagues and Peſtilential Diſtempers, up⯑on which I ſhall make a few Remarks in the following Chapter.

CHAP VII. Remarks on the Peſt and Peſtilential Fe⯑vers, as far as they are influenc'd by the Air.

I. THAT it is very difficult to come at Truth in the Hiſtory of Plagues; this is not to be wonder'd at, conſidering the Terror, Superſtition, and Credulity of the Vulgar, and the publick Diſorder during Peſtilential Seaſons. There never was any Plague better at⯑tended, nor better inquired into by Phy⯑ſicians, than the laſt of Marſeilles, yet the Facts (eſpecially thoſe relating to its original Cauſe) aſſerted by ſome of the Town Phyſicians, are as poſitively de⯑ny'd by the Phyſicians ſent down by the Regent, and perhaps upon a more exact Inquiry, and better Evidence.

[176] II. There is ſomething infamous as well as terrible in the Plague, ſo that no Nation will own it to be natural to their Country. ^* The Egyptians affirm it is brought to them from Barbary, Sy⯑ria, and Greece. The People again, in and about Conſtantinople, affirm as con⯑fidently, that it is brought to them from Egypt. As far as the Plague depends up⯑on the Air, theſe Queſtions ſeem natu⯑rally to ariſe: Whether any Conſtitu⯑tion of Air is capable of producing it in a Place where it was not brought by Infection? What Influence the Air has in propagating it? In a Matter both ſo uncertain and important, I ſhall hardly venture to determine poſitively, but lay the Evidence fairly before the Reader, and leave him to judge. And for the ſake of ſome Readers, I think it neceſſary to explain ſome Terms of Art.

III. An Endemial Diſeaſe is what is common to the People of the Country. A Diſeaſe is Epidemical, when it affects Multitudes, at any particular Seaſon or Time. A Sporadical Diſeaſe is an En⯑demial Diſeaſe, when in a particular Sea⯑ſon affects but a few People. I ſhall [177] likewiſe beg leave to adopt another Word. An Indigenous Diſeaſe is what is natural only to one Country, and from it propa⯑gated to others by Infection: For Ex⯑ample, The Small-pox was perhaps a Diſeaſe indiginous to Arabia, and from thence propagated amongſt all Mankind; but now in thoſe Places where it has once come, it may be properly ſaid to be Endemial or Popular, but not Indi⯑genous; there is no need of any new In⯑fection from its Original Country to carry it on; and it has become almoſt univer⯑ſal, miſſing few who live long enough to have it. This is manifeſtly different from the Caſe of the Plague; for tho' it has been at Times and great Intervals of Years in moſt Countries of Europe, and during thoſe Seaſons Epidemical, yet one can hardly call it Endemial, except in ſome Places of Turkey. Where the Plague invades and goes off regularly at ſtated Seaſons, it is probably there both an Indiginous and Endemial Diſ⯑eaſe.

IV. The Plague ſeems to be a parti⯑cular Diſeaſe, characteris'd with its pro⯑per Symptoms, which are nearly uni⯑form wherever it invades, an inflam⯑matory Diſtemper, with Eruptions upon the external Parts of the Body, in Buboes, [178] by the Inflammation and Suppuration of the axillary, inguinal, and other Glands, or in beginning Gangrenes, by Carbun⯑cles in ſome Parts, or Spots, red, livid, black, over all the Body; or laſtly, in Stigmata, or what they call the Tokens, which are Mortifications quite compleat, the Parts being inſenſible.

V. The Symptoms of the Plague re⯑ſemble thoſe of other inflammatory Diſ⯑tempers, with Eruptions, particularly St. Anthony's Fire, in which, after a con⯑tinued Fever of two Days, invading with a Rigor, there appears a Tumor, Diſcolo⯑ration, and a ſort of Carbuncles upon the Skin at the ſame time; the axillary Glands are often inflam'd, and ſome⯑times ſuppurated: This Analogy between the Plague and St. Anthony's Fire was obſerv'd by Dr. Sydenham. There is the ſame Analogy between the Plague and the Small-pox; the Fever invades in both Caſes with the ſame Symptoms; Pains in the Head, Back, Vomiting, Anxiety, ſparkling Eyes, high Colour in the Face, &c. This Fever after two Days pro⯑duceth, in the Plague, an Inflammation and Tumor in ſome Glands about the Head, Neck, Armpits, Groin; in the Small-pox the ſame in the Glands of the Skin: Theſe Glands, in both Caſes, [179] ſuppurating kindly, make what one may call a favourable Plague, or Small-pox; if thoſe Eruptions end in Gangrenes, in either Caſe, it proves the Diſeaſe to be dangerous or mortal, according to the Number or Condition of them. The ſudden Deaths in the Plague ſeem, as in the Small-pox, of ſuch as die in the firſt Stage of the Diſeaſe, only the Plague more malignant. The Progno⯑ſticks both in the Plague and Small-pox depend upon the ſame Principles, and the Danger in both to Subjects of the ſame kind: As to childing Women, young vigorous People after Irregulari⯑ties of Diet, in ſuch it begins with Hae⯑morrages, eſpecially bloody Urine, ſuch Symptoms being the Marks of the De⯑grees of Inflammation. Aſtriction of the Belly in the beginning of the Diſtemper is good in both Caſes. Buboes increaſing faſt, flatulent, without the natural In⯑flammation and Suppuration. Buboes too hard and horny, or with a Rainbow, that is, a Mortification about them, fa⯑tal in the Plague; in ſhort, Buboes well inflam'd, producing a laudable Matter, generally end well. Theſe Prognoſticks are analagous, and hold in the Small-pox: Nor do I mention theſe Things as ſtrange, ſince they depend upon the [180] ſame Cauſes, but only to ſhew that the Plague ſeems to be an inflammatory Diſ⯑temper of its own kind, like the Small-pox; the Havock made in the inward Parts by the Plague and Small-pox is much alike. What likewiſe proves the Plague to be a Species of Diſeaſe diffe⯑rent from all others, is, that if we can believe the Relations of Travellers, there are Countries where it never was at all, as the Eaſt-Indies, China, the Kingdom of Timquine, Cochine China, and moſt Places of the Weſt-Indies. Thoſe Conſiderations make it probable that it is a Diſeaſe indigenous to ſome Tract of Ground, and from thence propagated to other Places by Contagion: And yet,

VI. As to the firſt Queſtion, Whether the Air is capable of producing the Plague without Infection, in a Place where it is not an endemial Diſeaſe, I think the Affirmative is very probable; for Firſt, In a Country where it is both an indigenous and endemial Diſeaſe, it muſt be probably owing to ſome parti⯑cular Quality of the Air. Secondly, It has been prov'd by the Doctrine of the foregoing Part of this Eſſay, that there is hardly any Alteration, even to the ut⯑moſt Degree of Putrefaction but may be produc'd by the Enormities, Combina⯑tions, [181] and Alternations of the common Qualities of the Air; and that ſtill more extraordinary Effects may be produc'd by ſome Contagion of the Air, by uncom⯑mon Effluvia from Bodies near the Sur⯑face of the Earth. ^* A Philoſopher moſt learned in Phyſiology of the Air, gives Inſtances of Steams of a particu⯑lar Nature, being emitted from the Earth at particular times; that Mines will emit Steams noxious to Vegetables at parti⯑cular times; that there may be indeed ſome Tracts of Ground free from ſuch Minerals as emit thoſe noxious Effluvia, and conſequently free from the Plague, as proceeding from the local Qualities of their Air; but then thoſe Effluvia may be carried and mix'd with the Air of that Place by Winds. Mezeray tells us that the Plague which happen'd in France, in the Year 1346, the moſt u⯑niverſal and fatal that ever was known, began in the Kingdom of Cathay, by a Vapour moſt horridly foetid, that break⯑ing out of the Earth, like a kind of ſubterraneal Fire, conſumed and devour⯑ed above 200 Leagues of that Country, even to the Trees and Stones, and in⯑fected the Air after a wonderful man⯑ner; [182] that from thence it paſs'd through Aſia into Greece, Africa, and Europe. The learned Philoſopher above-mention'd gives Inſtances of the noxious Qualities, as well as abundance of ſome Minerals, particularly Orpiment; and of the Hurt⯑fulneſs of Arſenick, worn outwardly in Amulets, producing all the Symptoms of the Plague, and which were cur'd by anti⯑peſtilential and alexipharmick Remedies. There are credible Relations of Facts during the Plague of London, whereby it appear'd that the Air near peſtiferous Houſes diſcolour'd the Walls. There is nothing improbable in the Hypotheſis of extraordinary Effluvia. Thirdly, Thoſe Plagues which have cut off the greateſt Part of Mankind, in different and diſtant Countries, without mutual Commerce, muſt have an univerſal Cauſe, and there is hardly one imaginable beſides Air. There were two ſuch Plagues in the Time of Marc Anthony, and one in the Year 1450. Fourthly, There has been generally obſerv'd ſomething particular in the Seaſons and Conſtitutions of the Air, preceding the Plague, as great Droughts, laſting Southerly Winds, ſome⯑times laſting Calms; this was the Con⯑ſtitution always ſuſpected by Hippocrates and other ancient Phyſicians; ſuch was [183] that before the Plague of Nimiguen ^*. Great Droughts, as has been obſerv'd before, have been always found noxious to Human Bodies. The Conſtitution previous to the Plague of London, was very ſingular, a hard winter Froſt, laſt⯑ing till near the End of March, a ſud⯑den Thaw, the Ground cover'd with Water from melted Snow and Ice, and great Heats ſucceeding, Mankind being as it were in a Room flooded with Wa⯑ter with a great Fire. In ſome Places it has been obſerv'd, that the Exacerba⯑tion of the Diſeaſe kept time with the Lunations, raging moſt at the New and Full Moons; that there has been in pe⯑ſtilential Seaſons an unuſual Quantity of ſulphureous Vapours in the Air, Fleſh, and other animal Subſtances putrifying ſooner than ordinary, wild Birds leaving the infected Places, and tame ones dying in their Cages; all other Diſeaſes being more rife and mortal, and, as it were, participating of the Plague. Before the Plague of London, Inflammations of the Lungs were rife and mortal, as were likewiſe the Meazles. Fifthly, What ſeems to demonſtrate that the Diſeaſe depends upon ſome noxious Quali⯑ty [184] of the Air, is not only the Sudden⯑neſs of the Stroke, attended often with a Prediſpoſition of the Body: For Exam⯑ple, It has been obſerv'd that any thing which induceth a ſudden Change in the Motion or Qualities of the Blood, ſub⯑jects the Perſon to the Infection; in a Woman, Abortion, or Childbed, ſudden Paſſions of Fear, Anger, &c. all Exceſſes and Irregularities of Diet; young and florid Blood, rather than vapid and ca⯑chectical: All theſe Caſes reſemble a ſudden Taint of the animal Fluids by Air, as ſome Liquors are ſpoil'd by a Thunder-Storm, and, by the way, ſeem to demonſtrate, that the Contagion does not proceed from an animate Cauſe, for inviſible Inſects would bite or ſting, whether a Perſon was in a Paſſion or Calm; for here is a Concurrence of a Diſpoſition in the Fluids with ſomething which operates very ſuddenly upon them, which can hardly be ſuppos'd any thing beſides Air, inſinuating ſome Poiſon like that of a venomous Animal, and tainting the Blood when it is moſt agitated. Violent Exerciſe likewiſe diſpoſeth to the Peſtilential Infection, by admitting after it the Peſtilential Air through the Pores of the Body. The Diet which promotes a generous Perſpiration, with⯑out [185] inflaming, is the beſt Preſervative, and the Poor who are unprovided with ſuch Aliment, and moſt expoſed to the Air, ſuffer moſt; during a copious Per⯑ſpiration, the outward Air is not ſo much abſorb'd, and the noxious Quali⯑ties of the Air affect thoſe who are moſt expos'd to it. This agrees with Expe⯑rience, for the Europeans preſerve them⯑ſelves from the Plagues that rage in Turkey, by ſhutting themſelves up, which perhaps operates not only as avoiding the infected People, but the tainted Air. The beſt Remedies in the Plague are Diaphoreticks, ſuch as expel noxious Steams out of the Body. Theſe Obſer⯑vations ſeem to point at the Air as the efficient Cauſe of the Plague; but ſome of them indeed do not prove more than that Air is the Medium through which the Infection is propagated. And Sixth⯑ly, It has been obſerv'd that there is a great Analogy between the Symptoms of the Plague and St. Anthony's Fire, and that they differ only as to the Degrees of the Inflammation. Therefore I be⯑lieve hardly any one would venture to deny that a Conſtitution of Air which makes St. Anthony's Fire epidemical and violent in its Symptoms, heighten'd in its malignant Qualities, might poſſibly [186] carry the Eruptions upon the Skin from red to livid, from Inflammation to Mor⯑tification, and likewiſe the Inflamma⯑tion of the axillary and inguinal Glands to large Tumors and Suppurations, in which Caſe it would be term'd the Plague. Dr. Sydenham obſerves, that the epidemical Fever which preceded, attended, and ſucceeded the Plague of London, was the ſame with the Peſti⯑lential Fever, only during the Plague it was more violent, producing thoſe Erup⯑tions from which the Plague is denomi⯑nated. Seventhly, All the Symptoms of the Plague proceed from a high alka⯑line bilious Acrimony; this is evident from the Symptoms of the Diſeaſe, for one Effect is the ſame with the alkaline Salts, which raiſe an Eſchare; and by Experiments made during the Plague of Marſeilles, a ſmall Quantity of the Gall of a peſtiferous Body, mix'd with Water, and injected into the Vein of a Dog, infected immediately with all the Symptoms of the Plague, the Animal who had convers'd ſafely before in the Hoſpitals of the Infected: Such a bi⯑lious Acrimony is certainly producible by Air, and by many other Cauſes: Be⯑ſides, what demonſtrates a malignant Quality of the Air in a Peſtilential Sea⯑ſon, [187] is the great Mortality of other Diſ⯑eaſes; the whole Mortality during the Plague of London was 97306, the Mor⯑tality by the Plague 60506, whence the Mortality of other Diſeaſes muſt have been 28710, conſidering the great Emp⯑tineſs of the City at that time. This muſt needs have been above three times the common Proportion. From all theſe Conſiderations I think one may infer, that the Plague may be produc'd by ſome malignant Quality of the Air without any Contagion.

VII. But that the Air is the chief Inſtrument both of propagating and ex⯑tinguiſhing it, I believe no Body can deny; and this muſt be true from what Cauſe ſoever you deduce the Plague; if from an animate Cauſe, as from inviſi⯑ble Inſects, the favourable Conſtitution of the Air to their Propagation muſt be ſuppos'd; if from Infection of any kind, the Air is the Medium through which it is propagated, and muſt favour it, more or leſs, in different Seaſons, be⯑cauſe by the Change of the Qualities of the Air, it is quite extinguiſh'd, and, generally ſpeaking, by Cold; after the Peſtilential Seaſon is over, People return to their Houſes with Safety. I believe one may ſafely affirm, that there is hard⯑ly [188] any Year in which there are not in London, Fevers, with Buboes and Car⯑buncles; and that there are many Pete⯑chial or Spotted Fevers, is certain. What ſhall we call Diſeaſes with the ſame Symptoms, when they ſeize many or few in the firſt Caſe, when it ſpreads and turns epidemical and infec⯑tious, we call it the Plague; and when it does not ſpread perhaps it is the ſame Diſeaſe, only ſporadical; all this depends upon the Conſtitution of the Air.

VIII. It is no leſs clear that the Plague is often brought into infected Places by accident, and that it may, and neceſſarily muſt be ſpread by Con⯑tagion. Marſeilles, by its Commerce with Egypt and Turkey, has been more frequently infected with the Plague than any City in Europe. There are upon the Records of that City, an Account of Twenty great Plagues. By the Hiſto⯑ries of Plagues, and particularly that laſt of Marſeilles, the manner of ſpreading of the Diſeaſe ſeems to be gradual, at firſt ſeizing Houſes, then Streets, Quar⯑ters of the Town, and at laſt, like an univerſal Conflagration, the whole City. What was remarkable in the Plague of Marſeilles; an open and airy Street, [189] well perflated, where the better ſort of Inhabitants liv'd, was the laſt infected: This is eaſily accounted for from what was ſaid in the Firſt Chapter, about the Noxiouſneſs and Quantity of animal Steams. 1ſt. Let it be conſider'd to what a large Extent the Effluvia of ſome Bodies will infect the Air; for Exam⯑ple, the Snuff of a Candle: By what was ſaid in the Firſt Chapter, the per⯑ſpirable Matter of leſs than 3000 Hu⯑man Creatures would make an At⯑moſphere 71 Feet high, over an Acre of Ground, in 34 Days. This perſpi⯑rable Fluid is to Air in Denſity, per⯑haps as 800 to 1; therefore if you ex⯑tend the 3000 People over a hundred Acres of Ground, there will remain 8 Inches, the greateſt Part remaining un⯑blown off, and ſpread with the infinite Tenuity of odorous Effluvia, will infect the whole Air of that City. It is eaſy to conceive how the Steams of peſtife⯑rous Bodies may taint the Air, while they are alive and hot: but I think it appears likewiſe, by their being fre⯑quently opened and diſſected in Mar⯑ſeilles, without any Danger to the Chi⯑rurgeon or Aſſiſtants; that there is no Danger from them when cold, and not putrify'd. I think, from the Facts above-mention'd, [190] one may eaſily account for the Propagation and Continuance of the Plague in ſome Places infected, and the Preſervation of neighbouring Places from the Infection; if there is no par⯑ticular Diſpoſition in the Air to propa⯑gate the Diſtemper. Any infectious Diſ⯑temper is eaſily propagated amongſt Human Creatures living cloſe together. The Plague of Copenhagen, 1711, cut off the greateſt Part of the common Peo⯑ple, who are moſt narrowly lodged in that City.

IX. As to the Peſtilential Levains con⯑vey'd in Goods, it is a popular and ſafe Opinion; but many Writers about the Plague, and particularly Diemerbroke, ſeem to deſpite it. The Fact of its be⯑ing brought into Marſeilles by infected Goods, is poſitively aſſerted by the Town Phyſicians, and as poſitively deny'd upon a ſtricter Examination by thoſe ſent down by the Regent. In the laſt Plague of London, Dr. Hodges poſitively affirms that he ſaw a Patient in Weſtminſter with Carbuncles the Winter before the Plague broke out. As to the Plague being pro⯑pagated by infected Goods, there is this one Difficulty which is not eaſily ſolv'd. In a City infected with the Plague, notwithſtanding all the Pains taken by [191] artificial Purifications to extirpate the Contagion, there muſt be more of the peſtilential Levain left in Goods, than could be brought over in a whole Fleet; yet when the peſtilential Seaſon is over, People return to their Houſes, lie in the infected Beds, and uſe the ſame Goods ſafely: And indeed, if peſtilential Le⯑vains were always capable of producing the Infection, I cannot ſee how it is poſſible for the Plague ever to be ex⯑tinguiſh'd in a Place once infected. So that I think one may conclude, That the Conſtitution of the Air is the chief Inſtrument perhaps in producing, but ſurely in propagating and extinguiſhing this Diſtemper, and that there is no need (with Diemerbroke) to have Re⯑courſe to ſome miraculous Operation of Divine Vengeance. The moſt common and feeble Powers of Nature are capable of executing the Will of the Creator, e⯑ven in the extraordinary Diſpenſations of his Providence. The Inhabitants of thoſe Countries which have never been afflicted with the Plague, are not leſs Sin⯑ners than others. I think it likewiſe probable that the Turkiſh Contempt of the Contagion does not propagate the Diſeaſe more than the Chriſtian Dread of it, which brings publick Diſorder, [192] want of Care both of the Sound and Infected; for in general Contagions, more periſh for want of Care and Neceſſaries, than by the Malignity of the Diſeaſe; they being, as it were, ſequeſtrated from Mankind. In the Plague of Marſeilles many were buried alive. In the ſame Plague, when good Order was re-eſta⯑bliſh'd, of above 15000 who had gent⯑ler Symptoms, and were better attended, the greateſt Part recover'd. If the Turk⯑iſh Principles were join'd with the Chri⯑ſtian Care and Skill, no doubt the Ha⯑vock made by this Diſeaſe would be ſmall, in reſpect of what it is commonly in in⯑fected Cities.

X. As to the Method of Cure of this Diſtemper, it is foreign to my Subject; only by the Conformity of its Symptoms with other inflammatory Diſtempers, eſpecially the Small-pox, the ſame Me⯑thods ſeem be indicated in both. As to Preſervatives, there ſeems ſcarce any to be depended upon, but Flight from the infected Place. As the Diſeaſe ſeems to produce a general Diſſolution of the Blood in Haemorrages of all kinds (even thoſe Inflammations upon the Skin are Extravaſations of Blood ending in Mor⯑tifications) acid and ſtyptick Medicines are indicated, both as a Cure and Pre⯑ſervative, [193] it has likewiſe been obſerv'd by the Writers on this Diſeaſe, that it is apt to invade ſuch as are ſubject to intermitting Fevers, which often dege⯑nerate into the Plague. There has late⯑ly been diſcover'd in the Peruvian Bark a Virtue to reſiſt and cure Mortifica⯑tions; and what cures a Symptom, may preſerve from it: Therefore I would propoſe, in a peſtilential Conſtitution, the Peruvian Bark as an Antidote or Preſervative; it prevents as well as cures ſome ſorts of Fevers; it tempers bilious Acrimony; is ſtyptick; cures Haemorra⯑ges and reſiſts Mortifications; then why not uſe an Antidote ſo promiſing; if not effectual, at leaſt harmleſs. A Chirurgeon at Marſeilles told a Friend of mine, that he was ſure that he pre⯑ſerv'd himſelf from the Plague by ta⯑king large Doſes of the Bark; and that it had its Effect after he felt himſelf attack'd with the firſt Symptoms.

XI. There have been of late two re⯑markable Inſtances of the Influence of the Air in producing an Epidemical Diſ⯑eaſe, perhaps over the greateſt Part of the Surface of the Earth; the firſt hap⯑pen'd in the Year 1728; the laſt in the latter end of the Year 1732, and be⯑ginning of 1733; which being the more [194] recent and remarkable, I ſhall give a ſhort Deſcription of it, till a more par⯑ticular one can be procur'd from the collected Memoirs of the ſeveral Coun⯑tries which it invaded, of which I have ſeen only a few.

XII. The previous Conſtitution of the Air was, in England, and in the great⯑eſt Part of Europe, a great Drought, which may be inferr'd from the Failure of the Springs, in the Abatement of the freſh Water in all its uſual Cur⯑rents and Reſervoirs, which are the beſt Meaſure of the Quantity of Moi⯑ſture falling from the Clouds. What is moſt generally taken notice of in the Accounts I have ſeen from Germany, France, and ſome other Places, was, That the Air in the beginning of Win⯑ter, eſpecially in November, was more than uſually filled with thick and fre⯑quent Fogs, the Matter of which was not precipitated upon the Earth in Rain, Snow, or any other Fruits of the Air. Fogs are ſo uſual in this Country in November, that there was nothing par⯑ticular obſerv'd about them that I know. But there was hardly any thing fell from the Clouds during the Month of November, except a very ſmall Quanti⯑ty of Snow, attended with a Froſt of [195] no long Duration; and this was all the Winter we had. In the Northern Parts of France there was a very ſmall Quan⯑tity of Snow, which laſted from their 15th and our 4th of November, till af⯑ter Chriſtmas. This was ſucceeded by Southerly Winds and ſtinking Fogs, during which there was obſerv'd by ſome Chirurgeons a great Diſpoſition in Wounds to mortify. Both before and during the Continuance of the Diſeaſe in England, the Air was warm, beyond the uſual Temper of the Seaſon, with great Quantities of ſulphureous Vapours, producing great Storms of Wind from the South-Weſt, and ſometimes Lightning without Thunder.

XIII. As to the Time of Invaſion of the Diſeaſe, they were different in dif⯑ferent Countries. It invaded Saxony and the neighbouring Countries in Ger⯑many, about the 15th of November, and laſted in its Vigour till the 29th of the ſame Month. It was earlier in Holland than in England; earlier in E⯑dinburgh than in London. It was in New-England before it attack'd Bri⯑tain; in London, before it reach'd ſome other Places weſtward, as Oxford, Bath, &c. and, as far as I can collect from Accounts, it invaded the Northerly Parts [196] of Europe before the Southerly. It laſted in its Vigour in London, from about the middle of January 173⅔, for about 3 Weeks; the Bill of Mortality, from Tueſday the 23d to Tueſday the 30th of January, contain'd in all 1588, be⯑ing higher than any time ſince the Plague. It began in Paris about the beginning of their February, or the 21ſt of our January, and laſted till the be⯑ginning of their April, or the 21ſt of our March; and I think its Duration was longeſt in the ſoutherly Countries. It raged in Naples and the ſouthern Parts of Italy in our March. The Diſ⯑eaſe, in travelling from Place to Place, did not obſerve the Direction, but went often contrary to the Courſe of the Winds.

XIV. The Uniformity of the Symp⯑toms of the Diſeaſe in every Place was moſt remarkable. A ſmall Rigor or Chillineſs, ſucceeded with a Fever of a Duration (in ſuch as recover'd) ſeldom above three Days. This Fever was at⯑tended with a Headach, ſometimes Pains in the Back, Thirſt in no great Degree, a Catarrh or thin Defluxion, occaſion⯑ing Sneezing; a Coryza, or Running at the Noſe; a Cough with Expectoration of a thin Pituite at firſt, and afterwards [197] of a viſcous Matter; in which, if there was obſerv'd a clear oily Matter, it prov'd generally the Caſe to be mortal, for this clear Matter was purulent. Theſe were the moſt common Symp⯑toms: But a great many during that Seaſon were affected with Spitting of Blood, Pleuriſies, and Inflammations of the Lungs, dangerous, and often mor⯑tal; in ſome Places, particularly in France, the Fever after ſix or ſeven Days ended in miliary Eruptions; in Holland often in Impoſthumations of the Throat; in all the Blood was ſizy; and every where the Diſeaſe was parti⯑cularly fatal to aged People. What was obſervable was, that the Fever left a Debility and Dejection of Appetite and Spirits, much more than in Pro⯑portion to its Strength or Duration; and the Cough outlaſted the Fever in ſome more than ſix Weeks or two Months.

XV. There was during the whole Seaſon, a great Run of Hyſterical, Hy⯑pochondriacal, and Nervous Diſtempers; in ſhort, all the Symptoms of Relaxa⯑tion. Theſe Symptoms were ſo high in ſome as to produce a ſort of Fatui⯑ty or Madneſs, in which, for ſome Hours together, they would be ſeiz'd with a wandering of their Senſes, miſ⯑taking [198] their common Affairs; at the ſame time they had not any great De⯑gree of a Fever to confine them to their Beds; but in ſeveral who were thus affected, the Urine was obſerv'd of⯑ten to change from pale to turbid, al⯑ternately, ſo that there was ſome Fever; tho' I did not obſerve nor hear that the Bark was effectual, but the ſaline Febrifuge Draughts had generally a moſt ſurpriſing good Effect. Since this Diſeaſe has been over, the Air has con⯑tinued to be particularly noxious in Diſeaſes which affect the Lungs, and for that Reaſon occaſioning a great and unuſual Mortality of the Meazles, at the Rate of 40 in a Week, from which one has reaſon to expect ſome ſpeciali⯑ties in the Diſeaſes of the ſucceeding Seaſon.

XVI. The Remedies commonly ſuc⯑ceſsful in this epidemical catarrhous Fe⯑ver were Bleeding, Sweating, promoted by watery Diaphoreticks, Bliſters, and the common pectoral Medicines; and what I obſerv'd before, Febrifuge Draughts of Salt, of Wormwood, Juice of Limon, &c. I have not Particulars enough to enable me to enter into the Aetiology of this Diſtemper.

[199] XVII. It was Matter of Fact that there was a previous ill Conſtitution of the Air, noxious to animal Bodies. In Autumn, and long afterwards, a Mad⯑neſs among Dogs; the Horſes were ſeiz'd with the Catarrh before Mankind; and a Gentleman averr'd to me, that ſome Birds, particularly the Sparrows, left the Place where he was during the Sick⯑neſs.

XVIII. The previous great Drought, as has been obſerv'd before, muſt have been particularly hurtful to Mankind: Great Droughts exert their Effects af⯑ter the Surface of the Earth is again opened by Moiſture; and the Perſpira⯑tion of the Ground, which was long ſuppreſs'd, is ſuddenly reſtor'd. It is probable that the Earth then emits ſeveral new Effluvia hurtful to Hu⯑man Bodies; that this appear'd to be the Caſe by the thick and ſtinking Fogs which pr [...]ceeded the Rain that had fall'n before.

XIX. It is likewiſe evident that theſe Effluvia were not of any particular or mineral Nature, becauſe they were of a Subſtance that was common to every Part of the Surface of the Earth; and therefore one may conclude that they were watery Exhalations, or at leaſt [200] ſuch mix'd with other exhalable Sub⯑ſtances that are common to every Spot of Ground.

XX. Laſtly, It is agreeable to Expe⯑rience that watery Effluvia are hurtful to the Glands of the Windpipe and the Lungs, and productive of Catarrhs.

CHAP VIII. Of the Effects of natural Exploſions of the Air upon Human Bodies.

I. EXPLOSIONS of the Air by Lightning and Thunder, pro⯑duce more ſudden and terrible Effects upon Human Bodies, than any other Alterations of the Air whatſoever; therefore in a Hiſtory of the Effects of Air on Human Bodies, they ought not to be omitted; tho' there is little more to be ſaid of them than that their Ef⯑fects reſemble thoſe of Gunpowder, and other artificial Exploſions.

II. There may be imagin'd many na⯑tural Cauſes of thoſe violent Exploſions of the Air: Salts and Sulphurs (of which there are great Quantities in the Air) mix'd and kindled, will produce [201] great Exploſions: Nitre, Sulphur, and Charcoal, compoſe Gunpowder: Of Tar⯑tar, Nitre, and Sulphur, is compos'd the Pulvis Fulminans, which has a greater exploſive Force than Gunpowder: Acid Spirits and Chymical Oils produce Ex⯑ploſions: Filings of Iron, Sulphur, and Water, heat, flame, and at laſt produce Exploſions. Dr. Leiſter imagines Light⯑ning to be produc'd by the Pyrites; for the Vapour rais'd by Lightning ſeems, by ſome Obſervations, to have a magne⯑tical Quality, it having ſometimes chang'd the Polarity of Ships Com⯑paſſes^*. But I think they are naturally accounted for by the ingenious Mr. Hale, in his Appendix to his Treatiſe of Hae⯑moſtaticks, in which he has demonſtra⯑ted that ſulphureous Air and clear Air ferment together; therefore that Light⯑ning is produc'd by the Mixture of the freſh pure Air above the Clouds, with the ſulphureous Vapours that riſe below, which, when the Efferveſcence is over, cools the Air.

III. No Inſtrument of Art or Nature kills a Human Creature ſo ſuddenly as Lightning, they being often arreſted by [202] the Stroke, in the very ſame Poſture and Attitude in which they were ſtruck^*. The Effects and Marks on their Bodies se [...]m to proceed from two Cauſes, Burn⯑ing and Percuſſion; their Clothes being la⯑cerated and torn; their Bodies often pierc'd with Wounds, ſometimes round, reſem⯑bling thoſe from ſmall Shot, ſometimes of larger Diameters; theſe Wounds are with⯑out any Haemorrage, they being ſear'd or burnt at the ſame time: From their reſembling Gun Shot wounds ſo much, ſome have imagin'd that they were made by Hail produc'd that Inſtant; But whoever conſiders the Hiſtory of ſuch Accidents will find, that the Wounds are made by ſome penetrating Flame.

IV. In many Thunder-Storms there have been obſerv'd Balls of Fire perfect⯑ly round, which produce, as they move along, all the Effects of Percuſſion of a ſolid Body, which is very ſtrange; thoſe Meteors or Balls of Fire falling from the Clouds, have plow'd up and pierc'd the Ground very deep like a Bomb^†. Thoſe Balls of Fire have been likewiſe [203] obſerv'd upon meeting with any Obſta⯑cle, to divide themſelves into leſſer Striae; and it ſeems to me that thoſe cauteriz'd Wounds are produc'd by fiery piercing Darts or Balls. The Effects of Burn⯑ing appear often upon the Skin, which parch'd, ſhrivell'd, black, and burnt, the Flame taken in with the Breath has often ſhrivell'd the Lungs.

V. A ſecond Effect has been the mo⯑ving Bodies from the Place by the Blaſt, like that of being blown up by Gun⯑powder, of which there are many In⯑ſtances.

VI. A third Effect is a great Stroke from the Air, returning with great Vio⯑lence to reſtore the Balance after the Vacuity made; as upon the blowing up of a Powder-Mill, the Windows of adjacent Houſes are all bent and blown outwards, by the elaſtick Force of the Air within the Houſes exerting itſelf, by being deliver'd from the Counter⯑poiſe of the Air without: The Velo⯑city of the Air ruſhing into an ex⯑hauſted Receiver, is at the Rate of a Mile 4⅛ Seconds of Time, a Velocity of a Mile in ¼ of a Minute, is ca⯑pable of producing prodigious Effects. I have talk'd with Perſons who have [204] been near a Blaſt of Lightning, and have been knock'd down very near dead; they told me they felt a great Blow, as it had been from a hard Body: Many ſuch People, who have not been within the Action of the Flame, have recover'd from this Per⯑cuſſion. Bodies thunder-ſtruck have of⯑ten Contuſions upon them. There are ſome thunder-ſtruck People who have recover'd after a Fever attended with a Delirium; therefore ſuch as have been wounded are very hard to cure, as all Burns are. The Serpentine and crooked Dartings of Lightning are not occaſion'd by the Train of ſulphure⯑ous Vapours, for almoſt the ſame Ap⯑pearance happens upon ſtriking a glaſs exhauſted Receiver with the Palm of the Hand.

CHAP. IX. Practical Aphoriſms relating to the Air, drawn from the Doctrine of this Eſſay, And from other Writers of Epidemical Diſeaſes; of which ſome are certain, others confirm'd by ſome Obſervations, and are ſet down as Subjects of further Enquiry.

I. AIR is the Principle of Life, without which no Animal can ſubſiſt a Moment.

II. Good Air, as it is the chief In⯑ſtrument of Health, may juſtly be rec⯑kon'd amongſt the greateſt natural Bleſ⯑ſings. We find by the Influence of good Air whole Nations are able to ſupport the Want of many Comforts of Life with Chearfulneſs and Mirth; and the contrary is likewiſe true.

III. Mankind, by Reaſon and their la⯑comotive Faculty, have in ſome mea⯑ſure the Power of defending themſelves from the Injuries of the Air; but few have the Choice of the Air in which they live.

IV. Cuſtom enables human Creatures to ſupport the Effects of Air, and ren⯑ders the Alterations produc'd in their [206] Solids and Fluids familiar and leſs hurt⯑ful. By No VII. Chap. V. Animals by Cuſtom can better ſupport the Air-pump: Therefore.

V. Every Human Creature whoſe manner of Life demands, and whoſe Conſtitution can bear it, ought to inure themſelves to the outward Air, in ſeveral ſorts of Weather.

VI. In the Choice of Habitations for Mankind, the Wholſomneſs of the Air is a principal Conſideration.

VII. Air is as much a Particular in the Purchaſe of a Seat, as the Soil.

VIII. The Endemial Diſeaſes of tem⯑perate People are the Product of the Air; and the beſt Mark of the Wholſomneſs of the Air is the cuſtomary Longaevity of the Inhabitants, or the Rate of their Bills of Mortality.

IX. The local Qualities of the Air, de⯑pend upon the Exhalations of the Soil, and thoſe of its Neighbourhood, which may be brought thither by Winds.

X. A Soil, gravelly, chalky, ſandy, has but a ſmall Quantity of Perſpiration, for it imbibes Moiſture, and therefore is free from noxious Exhalations.

XI. From a rich, fat, marſhy Soil, a great Quantity and Variety of Vapours are rais'd by the Action of the Sun, [207] and the Heat communicated to the Sur⯑face of the Earth; which muſt at cer⯑tain Times and Seaſons variouſly affect the Inhabitants by its Contents, conſiſt⯑ing of Water, Oils, Salts, and ſeveral other Ingredients, of which the Analyſis of the Dew is the beſt Index; accord⯑ingly, rich Soils on the Banks of Riv⯑ers in hot Countries, are extremely un⯑healthy.

XII. Mere watery Exhalations perhaps are not ſo unwholſom: Soils which a⯑bound with theſe, are ſuch as retain Wa⯑ter, as Clay and level Grounds, where the Water ſtagnates; and ſpungy Grounds on the Tops of Hills, which attract Va⯑pours.

XIII. The Qualities of the Springs are the Mark of thoſe of the Air, for both the Air and Water imbibe the ſaline and mineral Exhalations of the Ground; therefore where the Water is ſweet and good, it is probable the Air is ſo likewiſe.

XIV. Dampneſs of Wainſcot, rotting of Furniture, tarniſhing of Metals, ruſt⯑ing of Iron, Effloreſcence of Salts upon any Bodies, Diſcolourations of Silks and Linen, are Marks of Salts of an unuſual Nature or Quality in the Air. See Chap. IV. No VIII.

[208] XV. The Steams of dry Ground, with⯑out any of thoſe noxious Qualities, are naturally wholſom and refreſhing upon opening with a Spade or Plow.

XVI. In chooſing Situations, Regard ought to be had to the local Steams of the neighbouring Soil; a gravelly Situa⯑tion may be render'd ſickly by the Air of a neighbouring Marſh, brought thither by Winds.

XVII. Epidemical Diſeaſes, which proceed from noxious local Steams, af⯑fect Cities leſs than the Country; for in Cities there is leſs Perſpiration from the Ground, and the Air is in ſome meaſure artificial: On the contrary, in dry Froſts, when the Perſpiration of the Ground is ſtopt, inflammatory epi⯑demical Diſeaſes affect the Citizens moſt, being more lazy and luxurious. See Chap. VI.

XVIII. The Air of Cities is not ſo friendly to the Lungs as that of the Country, for it is replete with ſulphu⯑reous Steams of Fuel, and the perſpira⯑ble Matter of Animals; therefore the Conſumptive and Aſthmatic are better in the Country.

XIX. The Air of Cities is unfriend⯑ly to Infants and Children. Every Ani⯑mal is adapted to the Uſe of freſh, [209] natural, and free Air; the Tolerance of artificial Air (as that of Cities) is the Ef⯑fect of Habit, which young Animals have not yet acquir'd. The great Mor⯑tality of Children under two Years, in London, is not intirely owing to the ſmall Care of the Brood of the Neceſſi⯑tous, and of Baſtards.

XX. The firſt Care in building of Cities, is to make them airy and well perflated; infectious Diſtempers muſt ne⯑ceſſarily be propagated amongſt Mankind living cloſe together.

XXI. Private Houſes ought to be per⯑flated once a Day, by opening Doors and Windows, to blow off the Animal Steams.

XXII. Houſes, for the ſake of Warmth fenc'd from Wind, and where the Car⯑penters Work is ſo nice as to exclude all outward Air, are not the moſt whol⯑ſom.

XXIII. People who paſs moſt of their Time in Air tainted with Steams of A⯑nimals, Fire, and Candles, are often af⯑fected with nervous Diſtempers. Living conſtantly in Air that kills Vegetables, cannot be wholſom for Animals.

XXIV. Burial-Places ought to be with⯑out the Precincts of great Cities.

[210] XXV. The Country Air in Spring and Summer has a conſiderable Influence up⯑on Mankind by the Steams of Vegeta⯑bles, which variouſly ſtimulate, and per⯑haps exhilerate the Spirits; and upon the ſame Account the Air of a planted and inclos'd Country is different from that of an open, and in ſome Caſes leſs re⯑freſhing.

XXVI. In great Latitudes, where the Difference of Heat and Cold are great, the Diet and Cloathing of the Inhabi⯑tants ought to vary with the Seaſon.

XXVII. The Qualities of Winter Air, as the Weight, Denſity, Coldneſs, Dry⯑neſs of Air in froſty Weather, are ſuch as induce a Stricture of the Fibres, and the Diſtempers are analogous: Therefore the Diet ought to be re⯑laxing, ſuch are the Uſe of tepid, wa⯑tery Liquors, and Bathing.

XXVIII. The copious Uſe of ſpiri⯑tuous Liquors is more hurtful in the Winter, and Evacuation better tolerated, not only by the greater Stricture of Fi⯑bres, but by reaſon of a more copious Aliment.

XXIX. Cold, in moſt People, increaſ⯑eth the Appetite: It is remarkable in the Hiſtory of ſuch as periſh'd by Cold [211] in Northern Countries, that they kept their Appetite to the laſt.

XXX. Exerciſe in the Winter is more eaſily tolerated; neceſſary for promoting Perſpiration, as the moſt durable and beſt Defence againſt outward Cold, and like⯑wiſe for the Digeſtion of a more groſs and copious Aliment.

XXXI. In Winter the Aliment, as well as the Weather, contribute to produce the Scurvy; to correct which, the Uſe of Vegetables, as far as they can be ſupply'd, is neceſſary in the Winter, and a Diet almoſt vegetable in the Spring; and the more ſo, becauſe then bilious Diſ⯑tempers begin to rage.

XXXII. Defences againſt intolerable Extremities of Heat, as Reſt, Shade, Venilation, Grottos, or Souterrains, are as neceſſary Preſervatives of Health, as thoſe againſt extreme Cold.

XXXIII. Air approaching to Animal Heat, or 90 Degrees, is dangerous, and the Effects of it more ſudden than of Cold: Heat exceeding 90 Degrees coa⯑gulates the White of an Egg: Hot Wea⯑ther, of long Duration, muſt produce great Alterations in Human Bodies.

XXXIV. The Heat of our Summer is ſeldom exceſſive or durable, and con⯑ſequently [212] not unhealthy: During the Summer in our Climate, many chroni⯑cal Diſtempers, and the acute ones of the Spring are ſilent.

XXXV. The Diſeaſes of our Sum⯑mers are moſt commonly the Effects of ſudden Alternations of Heat and Cold.

XXXVI. The moſt ſudden and dan⯑gerous Effects of Heat are from Inſola⯑ [...] or [...] of the Sun-beams.

XXXVII. The Heat of Air ought to be [...] manag'd, as not to produce too great [...], which thicken the Fluids and relax the Solids.

XXXVIII. Too great and ſudden Refrigeration by Ventilation, may be dan⯑gerous

XXXIX. Feveriſh Heat may be aba⯑ted by cool Air. The Management of the Air in the Patient's Room is a neceſ⯑ſary and important Piece of the Regi⯑men in acute Diſtempers. The too great Heat and Dryneſs, and other bad Qua⯑lities of the Air, have been often ſucceſs⯑fully tempered by the Steams of ſome Vegetables in a Patient's Room; eſpeci⯑ally of ſome of the ſoporiferous Kind, as Henbane, Cowſlips, Poppies, &c.

[213] XL. Great Colds ſucceeding great Heats, are productive of Diſeaſes; even cold Nights, after hot Days. Many of the acute Diſeaſes of Europeans in hot Countries, are occaſion'd by their expo⯑ſing themſelves incautiouſly to the ſerene or nightly Dew.

XLI. From the Effects of different Qualities of the Air, it is eaſy to deter⯑mine what Air is fit or unfit for what Conſtitutions. A moiſt Air relaxeth, therefore unfit for ſuch as have weak Fibres or are phlegmatick and bloated: A dry cold Air, with the Barometer high, contracts the Fibres, therefore apt to throw ſuch as have a ſtrict Conſtitution into inflammatory Diſtempers: A dry hot Air is unfit for the Lean, Scraggy, and Atrabilarious, and fit for ſuch as are of a contrary Conſtitution.

XLII. The beſt Indications for the Choice of Air are taken from the Conſti⯑tution of the Patient, and the popular Diſeaſes of the Inhabitants. The Air of France fit for Hypochondriacal and Sto⯑machicks: The Air of Holland, where Coughs are not frequent has been found better for ſome ſorts of Pulmonicks than that of warmer Countries: The Air of Countries which by Heat often diſpoſeth [214] to Spittings of Blood, promotes too great Sweating, and conſumes the muſcular Fleſh, can never be good for ſome ſorts of Conſumptions.

XLIII. The Scurvy of Seafaring Peo⯑ple is not merely the Effect of Salt Provi⯑ſions, but likewiſe of Moiſture.

XLIV. Great Alterations are produc'd in Human Bodies by great Enormities of the Seaſons, and by ſudden Altera⯑tions of the Weather from one Extreme to another, by Change of Situation into Air of contrary Qualities, as an Inhabi⯑tant of a cold Climate going into a hot one; by ſuch Changes the Solids and Flu⯑ids are agitated, and the Motions being uncuſtomary, ſtimulate more.

XLV. Air exceeding the natural Heat of the Body, cannot be long endured with Safety, eſpecially if the Humours are in an inflammatory State. I have known two Inſtances of malignant Fevers produc'd by the hot Air of a Bagnio.

XLVI. The Diet of the Inhabitants ought to vary with the Seaſon and Cli⯑mate; perhaps in a cold moiſt Air a great⯑er Indulgence in ſpirituous Liquors is al⯑lowable.

XLVII. In Seaſons, Climates, and Countries extremely hot, Cordials of [215] ſome ſort are neceſſary, ſuch as Wine and Spices.

XLVIII. The Diſeaſes proceeding from a cold and moiſt Air indicate Diapho⯑reticks.

XLIX. The Complexion of the Inha⯑bitants being clear and vivid, is a Sign of a wholſom Air; and contrariwiſe.

L. The Lungs of young People in the Prime of their Age are hot and tender, and being in immediate Con⯑tact with the outward Air, may be va⯑riouſly affected with its Contents and Qualities: Therefore the Choice of Air is of great Importance to Pulmonicks in thoſe of a more advanc'd Age. The Lungs are leſs hot, and more coreaceous or tough.

LI. The Mark of tender Fibres, even of the Lungs, is a vivid ſanguine Com⯑plexion: Tranſparency of the Skin is a Sign of Slenderneſs and Delicacy of its Fibres.

LII. Young Pulmonicks are ſubject to Conſumptions, and the old to Aſthmas.

LIII. Air charg'd with ſulphureous Steams, ſuch as that of Cities, is noxi⯑ous to Aſthmaticks; not only by the Dan⯑ger of Suffocation, but by the chronical Diſtempers induc'd by an imperfect Re⯑ſpiration; [216] for when the Reſpiration is im⯑perfect the Sanguification is ſo likewiſe.

LIV. Experience is the beſt Guide in the Choice of Air, or the Freedom of the Inhabitants from the Diſeaſe of the Pa⯑tient.

LV. A good Digeſtion depends upon Perſpiration and a good Sanguification, and that upon a good Reſpiration; there⯑fore the Choice of Air is of great Impor⯑tance to Stomachicks; a cold moiſt Air renders both the Perſpiration and Reſpi⯑ration imperfect.

LVI. The Earth may be conſider'd as a compound Body, under Digeſtion by Heat, by the different Degrees of which Heat there may be rais'd Effluvia of ſe⯑veral ſorts, ſucceeding one another; and epidemical Diſeaſes may be the Product of theſe Effluvia: Accordingly we find the Spring and Autumn to be Seaſons of epi⯑demical Diſeaſes: The Alterations of Heat are the greateſt before and after the Equinox, for then the Declination of the Sun changeth the faſteſt.

LVII. Epidemical Diſeaſes, with all the Specialities of their Character, de⯑pend upon the Conſtitution of the Air previous and preſent: A healthy Perſon, without any Error in the Non-natural, is [217] often ſeiz'd ſoon after his Arrival with the epidemical Diſeaſe of that Place.

LVIII. The Methods ſucceſsful in the Cure of epidemical Diſeaſes of one Seaſon, are often hurtful in thoſe of another; this Diverſity proceeds from the Tempe⯑rature of the Air, which is neceſſary not only to be obſerv'd, but to be recorded.

LIX. Great Heat and Cold ſucceeding one another, occaſion Pleuriſies and Quin⯑zies.

LX. Vernal and autumnal Diſeaſes, like Vegetables, come ſooner or later, as the Weather favours them. Hippocrates, in the Diſeaſes of the Autumn, takes notice of the nocturnal Acceſſions; in that Seaſon the Nights grow cooler and longer after hot Days.

LXI. Cholera Morbus is commonly con⯑fin'd to Auguſt, when the Bile is moſt ex⯑alted by great Heats, a ſtrong Perſpiration of the Day, and perhaps Abatement of it at Night; likewiſe by the too copious Uſe of cold Fruits.

LXII. The dangerous Symptoms of dif⯑ferent ſorts of acute Diſtempers of the ſame Seaſon, depend upon the Conſtitu⯑tion of the Air, and by reaſon of that univerſal Cauſe, the Methods ſucceſsful in one, ſeem to be indicated in the other.

[218] LXIII. The epidemical Diſeaſe, that is, the Maſter-Diſeaſe of the Seaſon, im⯑parts its Genius to the other Diſeaſes; as malignant Small-pox, and a malignant Fever without the Small-pox. The Fe⯑ver preceeding, accompanying, and ſuc⯑ceeding the Plague was the ſame. Dr. Sy⯑denham, from whom theſe ſix laſt Apho⯑riſms are deduc'd, confirms this Obſer⯑vation by ſeveral Inſtances: Therefore, according to the Opinion of the ſame ſa⯑gacious Perſon,

LXIV. It may be uſeful to Phyſick to give general Signatures and Names to Diſ⯑eaſes from the Seaſon.

LXV. There may be taken proper and uſeful Indications, both Preſervative and Curative, from the Qualities of the Air: What produceth Relaxation and Fluxili⯑ty ſeems to be indicated in Cold; Dia⯑phoreticks in moiſt; cooling, acid, ſtyp⯑tick Remedies, in hot and dry Air.

LXVI. No artificial Defences, as by keeping within Doors, are effectual a⯑gainſt a general Contagion of the Air; this was evident in the late epidemical Catarrh Fever: Yet ſuch Defences may abate ſomething of the Effect.

[219] LXIX. Moiſture that opens the Sur⯑face of the Earth, ſucceeding great Droughts which ſhut it, produceth a ſickly Conſtitution of the Seaſon; ſuch are Thaws after long Froſts, Rains after great Droughts.

LXX. Infants, by their pliant and ten⯑der Fibres, are more ſenſible of the Im⯑preſſions of Air than Adults; but as they muſt afterwards endure them, they ought to be made hardy by all ſafe Means; ſuch as have been inur'd to the Injuries of the outward Air, and accuſtom'd to a great Simplicity of Diet, are no more ſenſible of the Injuries of outward Air, than the Cattle. I know ſome ſtrong Inſtances of this.

What follows is deduc'd from the Epidemical Hiſtory of Germany.

LXXI. A watery Winter, ſucceeded by great Heats, often produceth malignant and mortal Fevers among Mankind, and Mortality amongſt Cattle.

LXXII. Epidemical and mortal Diſ⯑eaſes often ſucceed Earthquakes.

LXXIII. The Weather, and the epi⯑demical Diſeaſes of the ſame Climate, re⯑ſemble one another; the epidemical Hiſ⯑tory of Germany fits Britain.

[220] LXXIV. Like Weather produceth like Diſeaſes in every Seaſon; a warm Winter, Diſeaſes of the Spring; a cold and wet Summer, Catarrhs.

LXXV. Such as have had acute Diſ⯑tempers of one kind, are often affected with new and uniform Symptoms by the Enormities of the ſucceeding Seaſon.

LXXVI. Southerly Winds of long Du⯑ration often produce Petechial or Spotted Fevers.

LXXVII. From Rains after great Froſts in the Winter, glandulous Tumors and ſuffocative Catarrhs; from the ſame Conſtitution in the Spring, Quinzies and Spotted-Fevers; what was remarkable in ſuch a Seaſon, peſtilential Buboes former⯑ly cur'd, began to run.

LXXVIII. Diſeaſes of a very odd and peculiar Nature have ſometimes ſucceed⯑ed an inconſtant Seaſon, as Melancholy, Madneſs, Furor uterinus, which ſeem'd infectious; this at Mansfield, 1698.

LXXIX. From an April extremely cold and wet, all the Diſeaſes of the Winter, Madneſs, Epilepſies, Catarrhs of all kinds.

LXXX. In the Epidemical Hiſtory of Germany, many of the Obſervations of Hippocrates are confirm'd.

[221] LXXXI. From an unuſual Inconſtan⯑cy of the Weather, and perpetual Changes of the Wind from Eaſt to Weſt, epide⯑mical Dyſenteries.

LXXXII. From Extremity of Heat in the Dog-days, a rainy Seaſon, a malig⯑nant Spotted Fever.

LXXXIII. From Froſt and Snow in April and May, an extremely mortal Small-pox and Dyſentery in Autumn.

LXXXIV. From rainy Seaſons, Head-aches, Toothaches, Rheumatiſms, Aſth⯑mas.

LXXXV. From great Enormities of the Seaſons a great Run of epidemical Diſtempers.

LXXXVI. From frequent, great, and ſudden Changes of the Weather, acute Diſtempers with dangerous Symptoms.

LXXXVII. In orderly Seaſons the common popular Diſeaſes neither rife nor mortal.

LXXXVIII. From hoar Froſts in the Morning, ſucceeded by hot Days in the Summer, an unuſual Run of dangerous intermitting Fevers and Jaundices. Ac⯑cording to that of Hippocrates, from Heat and Cold in the ſame Day, expect Au⯑tumnal Diſeaſes.

[222] LXXXIX. The ſickly Conſtitution at⯑tending Thaws is mended by Winds blow⯑ing off the Vapours.

XC. From extreme and laſting Cold, a great Run of Apoplexies and other con⯑generous Diſeaſes, Catarrhs, Vertigoes.

XCI. From great Heat and Drought, burning continued Fevers, attended with Haemorrages, bilious Vomitings, and De⯑jections.

XCII. In Mildews which corrupt Ve⯑getables, the Morning and Evening Air dangerous. Northerly and Eaſterly Winds, which ſtop the Perſpiration of Vegetables (abating their Fragrancy) have probably the ſame Effect upon Mankind.

XCIII. Epidemical Diſeaſes depend not only on the preſent, but the previous Con⯑ſtitution both of the Air and Patient: A hot Seaſon often produceth the Scurvy and other cutaneous Irruptions; after pre⯑vious Cold there have been Scurvies, which were exaſperated by Heat, as that in the Memoirs of the Academy de Sci⯑ences.

XCIV. Weather which produceth no uneaſy Senſation in Human Bodies, is wholſom as long as it laſts; but the Indo⯑lence produc'd by ſuch Weather may make them more ſenſible of the Agita⯑tions, [223] both of their Fluids and Solids by the Change.

XCV. The epidemical Diſeaſes of Ani⯑mals much expos'd to the Air, and whoſe Diet is ſimple, depend upon the Conſti⯑tution of the Seaſon. The Difference of the Quality of the Fruits of the Ground operate likewiſe, but not ſo much as the Air.

XCVI. Journals of the Weather, Reign⯑ing Diſeaſes, and Remedies ſucceſsful, would be of great Uſe to Mankind, and more eſpecially to Phyſicians: From ſuch Journals perhaps it might be poſſible to predict both the Weather and the epide⯑mical Diſeaſes.

XCVII. In judging of the Conſtitution of the Air, many things beſides the Wea⯑ther ought to be obſerv'd: The Diſeaſes of Vegetables and Brutes; in ſome Coun⯑tries, the Silence of Graſhoppers; Want of Mellification in Bees; Deſertion of Birds; Quantities of Inſects; ſulphureous Vapours; Mortality of Diſeaſes common⯑ly not dangerous; ſuch things have been obſerv'd to be ſignificant.

XCVIII. In Cities infected with the Plague, the moſt effectual Care of the Police is an early and quick Separation of the infected Houſes, Streets, Quarters [224] of the City from the uninfected, with proper Aſſiſtance of the Sick, and a Re⯑moval of the other Inhabitants into ſome airy and well perflated Incampment, in Tents or Barracks.

XCIX. By good Government many of the Infected may be ſav'd, and many Sound preſerved from the Infection. In the Hiſtory of the Plague of Marſeilles, one may ſee the bad Effects of Confuſion and Neglect in the Beginning, and the good Effects of Order towards the End.

C. The Peruvian Bark has promiſing Qualities as an Antidote in a peſtilential Conſtitution.