w 



N 



W 



N 



\vhich_the air itfelf, aftcd on by the fame force^ will . they blow one! way half the year, and upon the opnci. 

 tT^r,i./> ;n tU^ r.^rr,^ firr-.^ u.r rU\. ..,1^ I fj|-^ points thc othcf half. 



Tnis that is here faid relates to the fea Winds, at feme 



diftance from the land; for upon the land, and near 



tbeiliores, the land and fea breezes are almoii ever/ 



... ^'^ere fenfible ; and the great variety that happens 



the air, by the fame impulfe, will move in tlie fame! m their periods, force, and direction, happens from 



the fituation of mountains, valleys, and \\oods, and 

 from the various texture of the foil, more or Icfs capa- 

 ble of retaining or reflecting heat, or of exhaling or 



move in the fame time by this rule. 

 I. As the fpecific gravity of air is to that of any 

 other fluid, fo reciprocaUy is the fquare of thc fpace 

 which that fluidj impelled by any force, moves in 

 any given time^ to the fquare of the fpace, which 



time. 



Suppofing therefore, the ratio of the fpecific gravity 

 of that other fluid to that of air, to be z=i?: c -, the 

 fpace defcribed by the fluid to be called /; and that 

 Ivhich the air will defcribe by thc fame impulfe x : the 

 rule gives us x=z^ {b s : c.) 



Hence, if we fuppofe water, impelled by the given 

 force, to move two feet in a fecond of time ; then 

 ■will/zr2 *, and fince the fpecific gravity of water to 

 air is as 970 to i, we fliall have X— 970, and c=zi ; 

 confecjuently x=^ 970. 4— y^ ^SSo=.6^2 feet : the 

 velocity of the Wind, therefore to that of water, 

 moved by the fame power, will be as 623 to 2 ; i. e. 



» 



623 feet. 

 2. Add, 



Wind 



/ 



{cx'-'.b',) and therefore the 



Ipace any fluid, impelled by any imprefllon, moves 

 in any time, is determined by finding a fourth pro- 



fpecific 



numbers 



Wind moves in the given time. The fquare root of 

 that fourth proportional is the fpace required. 

 M. Mariotte, e. g, found, by various experiments, 

 that a pretty ftrong Wind moves 24 feet in a fec^d 

 of time ; wherefore, if the fpace which the watef, a(ft- 

 ed on by the fame force as the air, will defcribe m the 

 fame time, be required, then will ^r:i, ;^=:24, bzzo^Oy 



f- 



Wind 



a 4 



■X 



%') 



the preffure required to produce that velocity, we 

 have this rule. / , • 



The fpace the Wind moves in one fecond of time, is 

 to the height a fluid is to be raifecj in an empty tube, 

 in or^er to have a preffure capable of producing that 

 velocity, in a"ratio compoynded of the fpecific eravi- 

 tjr of the fluid to that of air -, and of quadrupk the al- 

 titude a body defe"'^^ '^^^ tl^Trft fecond <rf time, to 

 the aforefaid fpace of air. 



v-'-r-' 



4^; ,V^ri' 



Suppofe, e. gr. the fpace the air moves in a fecond 

 ^=24 feet, or 288 inches; call the altitude of the 

 third x^ and the ratio of the mercury to the air b : 

 f =13580 : I, ^r:i8x inches ; x will be lefs than the 

 number by one line, or Vt of an inch. And hence 

 we fee why a fmall, but fudden change in the baro- 



Winds 



an anemometer, or Wind 



V 



The force, of the '^yind is d 



by a peculiar machine callec 

 meafurci; > "which being mc 



thl9^?9^ f >yi0dmill, raife a weight, that ftill the 

 higher it is raifed, receding farther from the center of 

 motion, by Aiding along a hollow arm fitted on to 

 the axis of the fails, Ipfcomes heavier and heavier, and 

 pr?.#s op th? arm, till, being a counterpoife to the 

 force of th? Wiad qn. the fails, it ftops the motion of 



them* Anind^xtheo, fitted. upon the fame axis, at 

 right angles with th^. a^-nj, bv its Vifing or falling, 

 --'-^soutthqUrengthof. the Wind, on a plane'di- 



like a did plate int;o degrees. 



Winds are either conttant or variah 



VI 



1 * t 



The 



^ - 



^?",^ are up an4, do>yn^ always at a certain time 

 the year, and m qertain,pa;;ts,Q^the world; butt 

 variable vary fo much, th^? diey qannpt be reduc 

 to any rule. . 



The conftant and periodical Winds are onlv in t 



*!^^^".^¥ "tropics, there is generally an eafterly Wind 

 all the year long, without any confi^erable variation, 

 unlefs declining fomefe.w points, toward, the north, or 



hundred leagues, t|ic fomhejly an4.fouth-weft Winds 

 are perpetuaL 





^.^ ■■*-' ■^-■^ ' 



^'V 





■ 



,- -^ ^>.- 



the Indian ocean the Winds are'partly general 



a 



'^- 



•t 



condenfing vapours. 



Of variable Winds, fome ar^ common to all countries 

 others are more peculiar to fome certain parts. 

 Of the latter forr, the moft famous are hurricanes 

 which chiefly infell the Caribbee illands, but are not 

 anniyerfary, nor equally frequent. 

 Their fwry is fo great, that they throw down all be- 

 fore them, tear up trees, overturn houftrs, tofs fliips 

 prodigioufly, and blow about tilings of a vaft wdaht 

 They are not even coritinOed Wmds, but bJow in 

 gufts, which fuddenly come and go ; ^eithtr dothey 

 extend very wide,- but are fometimcs confined to a 

 narrow compafs, and at other times take a larger fcopc 

 As for their duration, k is but a few days^ and fome-^ 

 times only for a few hours. They are mofe commari 

 m America: than any where elfe, but yet Europe and 

 Afia are nos altogether without them, as appears from 

 hiftories and travels. 



The caufes of tempefts and hurri'tanc*^ are hardly to' 

 be accounted for in all particulars. However it may, 

 in the firfl: place be noted, that the ratio of ail 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 from a high place, or if there be 

 a confluence of feverarftreams together, this gives a 

 vioknt motion^^ and caufes a many whirlings and ed- 

 dies in 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 muit be furious tempefts of Wind 

 railed m it. And fuqh a thing may happen, if any 



W 



extiraordinary 

 3yind, upon 

 get over, by ^ 



w;hicb oppofe them : for example; fuppofe 'a Wind^ 

 upon fpme point between north and eafl:, carries a 

 large colleftipn of vapours out of Africa into the Ca* 



^M^^S-'^^^^r this Wind lights upon the continent 

 9/. America;^ aowa if^ i^">oflible, that not only the 

 mountains and woods of Panama may refift the cur- 

 ^^nt.of this Wind, ?nd croud the vapours together 

 there ; but a contrary Wi^d, upon a point between 

 fouth and wefl:, may blow ^t the fame time upon the 

 weftern ftore of Am?ric^, which, (hall, force the va- 

 pours back again. When fuch ^ rencounter happens, 

 there mufl: be a wild uproar in, the air about the Ca- 

 ribbee iflands, ajid in aHthaura^/betw^en South. and 

 North America, and the vappurs iftthis. cii:cuiar rpo- 



^if>n.nmft need? be furious on ^l^ fides, juft. as it is in ' 

 the water. , . *.- ^:. . 



confluence of 



iM 



t 



where 



caufe violent eddies, \yhirl thipgs^bout thA^A^e cait 

 in them, fy/allpwing them up fpr \ iittjg time, and 



then throwing them, back again. 



- ■ 



This fhews us the reafpn. 



■t> 



. *-j 



ofh 



bodi 



h 



cular motion, is with great fury tofled backwards and 

 forwards, between the ground and the clouds : for as 

 the waters, of the rollinp- fea do not run to the fhores 

 in an even ftream, but in fuch waves as dafli by fits 

 and turns-, fo the coqrfe of a vioknt Wind is ia broken 

 and difl:ina blafts. 



though their 



Such tenapefts^do not extend very far^ 



bound? are^ijnccrtain, becaufe the neighbouring air 



civiner wav to them, thev Ipend themfelves in the 



progreis of their motion..; ■ ^:.- 



■ V < 



-Th 



Thusx 



H 



<-, - 



't| 



'l f 



