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Show wil W i Air, to be = 0:3 the Space defcrib’d by the Fluid to be called /; and that which the Air will defcribe by the fame Impulfe x: The Rule gives us w= (D5: c). Hence, if we fuppofe Water impell’d by the given Force, to move two Feet in a Se- cond of Time; then will f=:2 ; and fince the {pecifick Gravity of Water to Air, is as 970 tor, we fhall have b==970, and c==1; confequently x= 970. 4=Y 3880 632 Feet; the Velocity of the Wind, therefore, to that of Water, moved by the fame Power, will be as 623 to 2; ie. if Water move 2 Feet in a Second, the Wind wi!l fly 623 Feet, 2. Add, that f= (c x*: b) and therefoxe the Space any Fluid, impell’d by any {mpreffion, moves in any Time, is determin’d by finding a fourth Proportional to the two Numbers that exprefs the Ratio of the {peci- fick Gravity, and the Square of the Space the Wind moves in the given Time._-_— The Square Root of that fourth Proportional is the wi Winds are either conftant or variable. conftant Winds are up and down always at 4 certain Time of the Year, andin certain Parts acertain Place, which they cannot eafily get over, by reafon of Mountains or contrary Winds which oppofe them: For example, gathered; which being kept in by the Shoars i North and Eaft, carries a large Collection of Of the Qualities of Winds. of the World; but the variable vary fo much, that they cannot be reduced to any Rule, The conftant and periodical Winds are only in the wideft Seas; as in the Aflantick and Ethiopick Seas, between the Tropicks, there is generally an Eafterly Vindall the Yearlon g. without any confiderable Variation, unlefs de- clining fome few Points towards the North or South ; but all along the Coats of Guiney, for five hundred Leagues, the Southerly and South-weft Winds are perpetual. In the Indian Ocean the Winds are partly general, as in the Ethiopick Ocean, and partly periodical ; that is, they blow one Wayhalf the Year, and upon the Oppofite Points the other half. This that is here faid relates to the Sea Winds, at {ome Diftance from the Land 3. for upon the Land, andnear the Shores, the Land and Sea-Breezes are almoft every where fenSpace requir’d. fible; and the great Variety that happens in M. Mariotte, e. gr. found, by various Ex- their Periods, Force, and Direétion, happens periments, that a pretty ftrong Wind moves fromthe Situat ion of Mountains, Vallies, and 24 Feet ina Second of Time; wherefore, if Woods, and fromthe various Texture of the the Space which the Water, aGed on by the Soil, more or lefs capable of retaining orrefame Force as the Air, will defcribe in the flecting Heat, or of exhaling or condenfing fame Time, be requir’d: Then will c—=1. Vapours. *=24, b=970, and we fhall find f= Of variable Winds, fome are common to (576: 970 = 34), all Countries, others are more peculiar to fome 3. The V y of Wind being given, to de- particular Parts. termine the E refjure required to produce that Of the latter Sort, the moft famous are Velocity; we have this Rule. Hurricanes, which chiefly infeft the Caribbee The Space the Wind moves in one Second Ifands 5 but are not anniverfary, nor equally of Time, is to the Height a Fluid is to be frequent. raifed in an empty Tube, in order to have a Preffure capable of producing that Velocity ; ina Ratio compounded of the fpecifick Gra- vity of the Fluid to that of Air, and of qua- druple the Altitude a Body defcends in the firft Second of Time, to the aforefaid Space ofAir. Suppofe, ¢. gr. the Space the Air moves in a Second a= 24 Feet, or 288 Inches ; call the Altitude of the third *, and the Ratio of Mercury to the Air 2: == 1BG8O0: Ly d=18r Inches; « will be lefg than the Num. ber by one Line, or z+ of an Inch. And hence we fee why a fmall, but fudden Change % So in the Barometer, fhould ke follow’d with violent Winds. The Force of the Windis determin’d experimentally, by a peculiar Machine call’d an Anemometer, or Wind-Meq urer, moved by means of Sails, which being like thofe of a Wind-mill, raifes a Weight, that {till the higher it is raifed, receding further from the Center of Motion, by fliding along an hollow Arm fitted on to the Axis of the Sails, becomes heavier and heavier, and preffes on the Arm, “till being a Counterpoife to the Force of the Wind on the Sails, it {tops the Motion of them. An Index then fitted upon the fame Axis, at right Angles with the Arm, by its Rifing or F alling Points out the Strength of the Wind, on a Plane divided like a Dial-P late, into Degrees, wi The The Fury is fo great, that they throw down all before them, tear up Trees, overturn Houfes, tofs Ships prodigioufly, and blow about Things of vaft Weight. even, They are not continued Winds, but blow in Gutts, which fuddenly come and go; neither do they extend very wide, but are fometimes confin’d to a narrow Compafs, and at other times take a larger Scope. As for their Duration, it is but a few Days, and fometimes only for a few Hours.. They are more common in America than any were elfe; but yet Europe and Aji are not altogether without them, as appears from Hiftories and Travels, The Caufes of Tempefts and Hurricanes are hardly to be accounted for in all Particulars. However, it mayin the firft Place be noted, that the Ratio of all Liquids is much the fame, and therefore an extraordinary Motion may be excited in the Air, by the fame Way as in Water. Now, if Water fall froma high Place, or if there be a Confluence of feveral Streams together, this gives a violent Motion, and caufes many Whirlings and Eddiesin it. This is apparent in the Torrents falling down the Rocks, and the Confluence of Rivers. If therefore fomething analogous may happen in the Air, there needs mutt befurious Tempefts of Wind rais’d in it, And fuch a thing may happen, if any extraordinary Quan- tity of Vapours be drawn by the Wind, vp a certain Suppofe a Wind upon fome Point between of America, mutt neceffarily be driven about the Caribbee Ulands. Vapours out of Africa into the Caribbee Ifles, this Wind lights upon the Continent of America; now it is poffible that not only the Mountains and Woods of Panama mayrefift the Current of this ind, and crowd the Vapours together there; but a contrary Wind upon a Point between South and Weit, may blow at the fame time upon the weftern Shoar of America, which fhall force the Vapours back again. When fucha Rencounter happens, there muft be a wild Uproarin the Air about the Caribbee Vlands, and in afl that Traé& between South and North America; and the Vapours in this circular Motion muft needs be furious on all Sides, juft as it is in the Water. For we fee in the Confluence of two Rivers, if their Currents are rapid at the Place where they fall in, they canfe violent Eddies, whirl things about that are caft in them, {wallowing themup fora little Time, andthen throwing them up again. This fhews us the Reafon, why heavy Bodies are often toffed in the Air by the whirling of Hurricanes, and then dafh’d to the Ground again: For the Airbeing a circular Motion, is with great Fury toffed backwards and forwards, between the Ground and the Clouds. For as the Waters of the rolling Sea do not run to the Shoars in an even Stream, but in fuch Waves as dafh by Fits and Turns; fo the Courfe of a violent Wind is in broken and diftin Blafts. Such Tempefts do not extend very far (though their Boundsare uncertain) becaufe the neighbouring Air giving way to them, they {pend themielves in the Progrefs of their Motion. Thus when a great Stone is caft into the Water, we fee a great Agitation round about the Place where it fell; but the more the Waves retire from the Center of Motion, the flower and the lefs fenfible they grow: Andas fuch Motions do not laft long in Water, no more do they in the Air, for the fame Reafon. Though there may be unufual Storms of Wind any where, the Air and Vapours are drawti together thereabouts by contrary Winds; yet they are more frequent about the Caribbce Iflands, efpecially in Fune and Auguf?, when the Sunis vertical there ; for their Air being rarefied by the Sun’s Heat, the ufual Winds bring thither a vaft Qauntity of Air and Vapours, which being crowded together in the Gulf of America, caufe a great Eftuation about the neighbouring Iflands. 4 Wind that blows from the Sea is ¢ moift, 7% Summerit is cold, i unle{s the Sea be froze up: 'This is well de {trated thus; there is Vapour continuallyr out of all Water, (as appears even hence, that a Quantity of Water being left alite while in an open Veffel, is found fenfibly diminifhed) but efpecially if it be expos’d to the Sun’s Rays; in which Cafe the Evaporation is beyond all Expe@tation. By this Means the Air incumbent on the Sea becomes impregnated with a deal of Vapour; but the Wir blowing from off the Sea, iweep thefe Vapours along with them ; and confequentlyare always moift. Again, Water in Summer, &c, conceives lefs Heat than Terreftrial Bodies, expofed to the fame Rays of the Sun; but in Winter, Sea Water is warmer than the Earth, cover’d with Froft; Snow, €c. “Wherefore, as the Air, contiguous to any Body, is found to partake of its Heat and Cold, the Air, contiguous to Sea Water, will be warmer in Winter, and colder in Summer, than that contiguous to the Earth: Or thus, Vapours raifed from Water by the Sun’s Warmth in Winter, are warmer than the Airtheyrife in, as appears from the Vapours condenfing and becoming vifible almoft affoon as they are got out into the Air: Frefh Quantities of Vapours therefore continually warming the Atmofphere over the Sea, will raife its Heat beyond that over the Land. Again, the Sun’s Rays reflected from the Earth into the Air, in Summer, are much more than thofe from the Waterinto the Air: The Air therefore over the Earth, warmed bythe Reflection of more Rays than that over Water, is warmer, —- Hence Sea Winds make cloudy, hazy Weather. 2. Winds which blow from the Continent are always dry, in Summer warm, and cold in Winter : —-—-- For there is much lefs Vapour arifing from the Earth, than from Water ; and therefore the Air over the Continent will be impregnated with much fewer Vapours: Add, that the Vapours or Exhalations raifed by a great Degree of Heat out of the Earth, are much finer and lefs {enfible than thofe from Water :———-'The Wind therefore blowing over the Continent, carries but little Vapour with it; and is therefore dry. Further, the Earth, in Summer, is warmer than Waterexpofed to the fame Rays of the Sun: —— Hence, asthe Air partakes of the Whenthe Sun is onthis Side the Equator, Heat of contiguous Bodies, that over the Earth the Air is more rarefied thereabouts, andit in Summer, will be warmer than that over the may fo happen, that the South-South-Eaft Water ; therefore the Wind, &e. After the like Manner ir is fhewn, that the Wind which conftantly blows beyond the Line, mayfometimes tranfgrefs its Limits, and bring Land Winds are cold in Winter: -——Hence the Vapours of the Etbiopick Sea to the fame we fee why Land Wiuds make clear, cold Place where thofe of the 4t/antick are already Weather. 9 P Our |