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Show Wi Wi wi But as the cool and denfe Air, by reafon of the greater Gravity, prefles upon the hot ane rarehed, ’tis demonftrative that this latter muft afcend ina continued Stream, as faft as able Monfoons ; andin the Southern, there fhould difperfe itfelf to preferve the Equilibrium 5 | is, by a contrary Current the upper Air mitt move from thofe Parts where the greateft Heat The Reverend Mr. Robinfon gives this Account of the Origin of Wind; That in the greateft Probability it proceeds from vatt Swarms of nitrous Particles, which rife from the Bottom of the Sea; which having been it rarefies ; andthat being afcended, it muft is; fo, by a kind of Circulation, the NorthEaft Trade Wind below will be attended with a t That this is more than a bare Conjecture, the almoft inftantaneous Change of the Wind to the oppofite Point, whichis frequently foundin paffing the Limits be a conftant Seuth-Eaf. This Account of Wind is taken from the Learned Dr. Halley’s Difcourfe on this Subject. Philofoph. Tranfattions, N° 183. ; / put into Motion, either by the central Fire, or by that Heat and Fermentation, which do aboundin this huge Body of the Earth; and therefore this firft Commotion, whichis ex- of the Irade Winds, feems to affure us 3 but cited by the faid Fermentation is called a that which above all confirms this Hypothefis, is the Phenomenon of the Monjoons, by this means moft eafily folved, and without it hardly explicable. , 7 Suppofing therefore fuch a Circulation 4s above, *tis to be confidered, that to the Northward of the Indian Ocean, there is every where Land within the ufual Limits of the by Porpoifes and other Sea Fifh, that delight to fport and play upon the Waves of the Sea, and do by their playing give to the Mariners the firft Notice of an approaching Storm. When thefe nitrous Swarms are rifen towards the Surface of the Sea, they caufe, in a Latitude of Thirty ; viz. Arabia, Perfia, Tn~ Bottom Wind, which is prefently difcovered dark Night, fuch a fhining Light upon the Waves, as if the Sea were on Fire, and being dia, &c. which for the fame Reafon as the delivered from the brackifh Water, andreMediterranean Parts of Africa, are fubject to ceived into the open Air, thofe fiery and unfufferable Heats when the Sun is to the fhining Meteors which fix upon the Maits and North, paffing nearly vertical; but yet are Sides of the Ships, are only nitrous Partemperate enough, when the Sun is remov’d ticles condenfed by the circumambient Cold, towards the other Tropick, becaufe of a Ridge and like that which the Chymifts call Pho/of Mountains at fome Diitance within the phorus, or artificial Glow-worm, fhine and f Land, faid to be frequently in Winter covered caft a Light, but have no Heat. This gives the fecond Notice to Mariners with Snow, over which the Air, as it pafles, that the Stormis rifing, for the Sea begins to muft needs be much chilled. ’ Hence it comes to pafs, that the Air com- be rough upon the firft breaking out of the ing, according to the general Rule, out of Wind, and the Waves fwell and rife, tho’ the | the North-Eajt in the Indian Sea, is fometimes Air at the fame Time is calm and clear. This boiling Fermentation of the Sea caufes hotter, fometimes colder than that which by this Circulation is return’d out of the Soutb- the Vapours to arife, which, by the IntenfeWeft, and, by confequence, fometimes the un- nefs ofthe circumambient Cold, are condenfed der Current or Wind, is from the North-Eaft, into thick Clouds and fall down in Storms of Wind and Rain; firft upon the Sea from fometimes from the South-Weft. North by the Fall of Snow or Hail; and in a cold frofty Morning, to fee the Wind North, the North-eaft Winds And the Intenfenefs of the atmofpherical Cold, having attracted the Vapours into the to the North by Weft, and fometimes to other Andit is undoubtedly from the fame Princi- s when the Sun draws near the T79; Q ; But in this latter, occurs a Difficulty not well to be accounted for, which is, why this Change of the Monfoons fhould be any more in this Ocean, than in the fame Latitudes in the Ethiopick, where there is nothing more certain than a South-Eajt Wind all the Year. It is likewife very hard to conceive, why the Limits of the Trade Winds fhould be fixed about the thirtieth Degree of Latitude all round Southerly Wind, on a fudden, changed to the Southward of the Equator, in Part things growing cooler Northward, and the Heat increafing to the So enter and blowall the Wi er, till April again. the Globe; and that they fhould fo fel- om tranfrefs or fall fhort of thofe Bounds ; as alfo that in the Indian Sea, only the whence they rofe, and then the attractive Power of the Mountain Cold, by a fecret Magnetifin between Vapour and Cold, attracts the waterifh Vapours, and intermix, with nitrous Particles, afcend to the high Tops of Mountains and Hills, where they hang hovering in thick Fogs and watery Mifts, until the atmofpherical Heat rarefies the nitrous Part of the Fog, which is always uppermoft, and colder Regions of the Air, where theyare condenfed into Clouds, the Wind breaks, diffi- pates anddrives them beforeit, till theyfall Points; the Clouds at the fame Time flying fome North by Weft and fome South-wett ; that about one o’Clockit rained apace, the then down in Rain, and water the Surface of the Clouds fometimes flying North-eaft, Earth. Andthis feems to be the Reafon why they have fettled North by Weft, and that at that have but little Wind, andlefs Rain in Agyp!, and thofe level Countries where they have no Mountains. Mr. Derhamfays, Wind is a Currrent ofthe Air, and that which excites or alters its Cur- rents may juftly be faid to be the Caule of Via Vind. No, thern Part fhould be {i oye to the change~ An and Clouds, from the Northward towar ds the South, To this a certain Author replies ; Several learned and ingenious Men have advanced feveral Speculations, in order to account for the Produétions of the Wind, or Current of the Air, and have, in fome mea- fure, accounted for fome particular Breezes or conftant Winds; yet we are ftill at a Lofs to determine from whence the Agitations of (according to the Opinion of fome ingenious the Air in general do arife, or to aflign the Men) the daily Progrefs of the Sun roundthat Caufes of the violen t Motions and alterable Part of the Globe, and by his Heat rarefying Courfes of it. one Part of the Air, while the cooler and heaSome Suppofe the Heat of the Sun to be vier Air behind preffes after. an Agent therein, by rarefying certain Parts And fo the Land and Sea Breezes, and fo of the Atmofphere . in our Climate the Northerly and Southerly To this another ingenious Author fuppofes Winds (which are commonly efteem’d the as follows: That the Heat of the Sun rareCaufe of warm and cold Weather) are really fying the Atmofphere, cannot be imagined to the Effects of the Cold or Warmth of the produce a Storm, or occafion the fudden Ges Atmofphere. neration of a great Wind: Nor upon this Of this, Mr. Derbam fays, he has had fo Suppofition can the fame Winds be expected. many Confirmations, that he does not doubt in the Night, when the Sun is abfent, as in of it; and he produces for an Inftance of it, the Day-time, when he is prefent ; or that that it is not uncommon to fee a warm there fhould be any Winds in thofe larger La- appears white andtranflucent, into brisk Gales otfWind, aay) April, when the Sun begins to warm thofe Countries to the North, the South-Weft Monbegin, and blow during the Heat till when the Sun being retired, and all ple, that the Clouds, &&e¢. It is obferved of Caves, that they do always emit Winds, more or lefs; and as great Caves, fo great Lakes alfo fend forth Winds ; but the moft univerfal and conftant Alterations ae Atmofphere are produced by Heat and ‘old. This is manifeft in the general Trade-winds, which between the Tropicks blow all the Year from Eaft to Weft: If the Caufe of this be and to wheel about toward the Southerly Quarters, when the Sun has well warm’d the Air; andthen again, in the cold Evening to turn Northerly or Eafterly. And hence alfo it is, that the Winds and Clouds are oftentimes contrary to one another in Thunder Showers (efpecially if Hail falls), the fultry Weather below directing the Wind one way,.and the Cold above the Clouds another way. And that he has obfery’d feveral Times, that when the Morning has been warm, and what Wind was ftirring was Weft-fouth-wett, that the Clouds were thick andblack(as they generally are when Snow follows) ; and that a little before Noon, the Wind veered about That this has no other Caufe, is clear from the Times wherein thofe Winds fet, viz. in of the Jud fucceed the Wit An Aquipoife of the Atmofphere produces Secondly, That the Strugsle betwe en the a Calm; but if that Aquipoife be taken off, Warmthof our Region and the Cold of the more or lefs, a Stream of Air or Wind is ac- cloudy Region, ftopp’d the airy Currents of cordingly thereby produced, either ftronger or both Regio ns, weaker, fwifter or flower, Thirdly, That the Falling of the Snow And there are divers Things thas may caufe through our warme r Air, did at firft melt infuch Alterations in the A.quipoife or Ballance to Rain, but after the fuperior Cold had of the Atmofphere, viz. Eruptions of Va- conguer’d the inferior Warmth, it became pours from the Sea and Land, Rarefaétions Sleet. and Condenfations in one Place more than Fourthly, That as the Cold prevai l’d by in another, ‘the Falling of Rain, Preffure of Degrees, it wheel’d about both the Winds North, and at laft both Wind and Clouds Time the Sleet fell very plentifully, andit titudes of the Earth, where, in the Winters there is fcarce a fenfible Difference of the Sun’s Heat in the Day more than in the Night, whereas there are more Winds foundto be in thofe Parts than in hotter Climates, and are greateft in the Winter. Befides, there are many more Objections that over-turn this Probability of the Rife of Wind. He adds, That in order to trace out the Caufes of the Wind by Effeéts and Phe mena, we may obferve, that Wind is gene- rally attended with a cloudy Sky, and that there are more Winds in the Winter, when there is more Rain and obfcure Weather, than in the Summer; and likewife in our Northerly Climates than in leffer Latitudes, that more ufually are attended with a fair and ferene Atmofphere, which makes it probable, that the aqueous Vapours that are fuftained in the Air, from whence proceed Clouds and Rains, may be the Foundation of Winds, It is paft all Difpute, that there is always a vaft Quantity of Vapours contain’d in the Atmofphere, as is manifeft from the great Quantity of Water that is conftantly dif- charg’d from thence in Rain, Snow, Se. And grew very cold. Fromall which he obferves ; Firft, That though the Region below was by the Surface of the Seas and Riversin the warm, the Region ofthe Clouds was cold, as World, and diffus’d in the Atmofphere the black Snowy Clouds fhew’d. Dr. Halley has given us a curious Eftimate of the vaft Quantity of Water wafted in Vapours 990 |