Win
■KWind, therefore, will blow out of a place, in which the Airisfuddenlyrarefy'd: And on this Principle, in all pro- bability, it is, that,
I. Mod Caves are found to emit Wind, either wore or le Is. Since the Sun's Power in rarefying the Air, ii no- torious ; it muft neceffarily have a great influence or the Generation of Winds.
The riling and changing of the Wind is determin'd ex- perimentally, by means of Weather-cocks, placed a-top of
•Houfes, (Sc. But thefe only indicate what paffes about
their own Height, or near the Surface of the Earth : Wol- fius alluring us, from Obfervations of feveral Tears, that the higher Winds which drive the Clouds, are different
from the lower ones, which move the Weather-cocks
Mr. Tlerham obferves fomething not unlike this; ThvC. Theol. l.i. c. 2.
The Author laft mention'd obferves, upon comparing feveral Series of Obfervations made of the Winds in diver" Countries, viz. England, Ireland, Switzerland, Italy, France, New England, He. That the Winds in tbofe feve- ral places feldom agree ; but when they do, it is common- ly when they are flrong, and of long continuance in the iame Quarter ; and more, he thinks, in the Northerly and Eaflerly, than in other Points — Alfo, that a flrong Wind in one place, is oftentimes a weak one in another; or mo- derate, according as the places are nearer, or more re- mote. 'Philofoph.Tranfacl. N J 2)7, and 311.
Laws of the Force, and Velocity o/Wind.
Wind being only Air in Motion, and Air being a Fluid, fubjeet to the Laws of other Fluids ; its Force may be
[*»"]
WIN
Sails, becomes heavier and heavier, and preffes on the &,mi till being a Counter-poife to the Force of the Wind on the Sails, it flops the Motion thereof. An Index, then, fitted upon the fame Axis at tight Angles with the Arm, by its ruing or falling, points out the Strengd, of the Wind, on a Plane divided like a Dial-Plate into Degrees. See Ane-
MOMETER,
Vitalities of Winds.
i. A Wind Mowing from the Sea, is always moilt : In Summer, us cold. ; , and in Winter, warm : unlefs the Sea. be froze up— This is well demonflrated thus: There is Vapour continually riling out of all Water, (as appears e- ven hence, that a Quantity of Water being left a little w r h,le . '" a " °P en Veffel > is f °™<l fenfibly diminifh'd) but elpecialy i( it be expos'd to the Sun's Rays ; in which Cale, the Evaporation is beyond all expeflation. See Va- pour.] By this means, the Air incumbent on the Sea
becomes impregnated with a deal of Vapour. But the' Winds blowing from off the Sea, fweep thefe Vapours a- long with them; and confcquently ate always moilt.
Again, Water in Summer, Sic. conceives lefs Heat than terreftrial Bodies expos'd to the fame Rays of the Sun ; but in Winter, Sea-Water is warmer than the Earth co- ver'd with Ftoft and 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 rais'd from Water by
the Sun's Warmth in Winter, is warmer than the Air it
- rifes in ; (as appears from the Vapours condenfinff and be-
brought ,0 a precfe Computation: Thus— the Ratio of coming vf.ble almofl as foon Jthev "« eo^fn™ Airl
the fpecific Gravity of any other Bind, ,0 that of Air, to- Frefh Quantities of Vapour, therefore contnTalv warm
ppther ninth the. Share that. J?l„;j i^-holl'A /,., *£* m— /K -__ .ijS. r . r '. l »ercrore, continually warm-
gether with the Space that Fluid impell'd by the 'Prejfure of the Air, moves in any given 'time, being given ; we ■can determine the Space which the Air itfelf, a&ed on by the fame Force, will move in the fame time : By this Rule,
1. As the fpecific Gravity of Air, is to that of any other Fluid; fo, reciprocally, is the Square of the Space which that Fluid, impell'd by any Force, moves in any given time, to the Square of the Space which the Air, by the fame Impulfe, will move in the fame time.
Suppofing, therefore, the Ratio of the Specific Gravity And therefore the Ai
e Atmofphere over the Sea, will raife its Heat be- yond that of the Air over the Land Again, the Sun's
Rays refleaed from the Earth into the Air, in Summer, ate much more than thofe from the Water into &ir : The Air therefore over the Earth, warm'd by the Refeaion of more Rays than that over Water, is warmer Heuce Sea- Winds make thick, cloudy, hazy Weather. _ 2. Winds blowing from the Continent, are always dry ;
in Summer, warm ; and cold in Winter For there is
much lefs Vapour ariling from the Earth, than from Water.
- , if we fuppofe Water impell'd by the given Force, nent, carries but little Vapo!
two Feet in a Second of Time; then will/= 2 ; dry.
•es
Hence to move
and fince the fpecific Gravity of Water to the Air, is as 970 to 1 j we /hall have ^ = ^70, and c=i ; confequent- ly* = V / 5>7c- 4 = / 3880 = 52; Feet. The Velocity of the Wind, therefore, to that of Water moved by the famePowet, will be as 623 to 2 ; i.e. if Water move two Feet in a Second, the Wind will fly 623 Feet.
2. Add, that /= •/ (cx':b) and therefore the Space any- Fluid, impell'd by any Impreflion, moves in any time, is determin'd, by finding a fourth Proportional to the two lumbers that exptefs the Ratio of the fpecific Gravity, and the Squate of the Space the Wind moves in, in the'
given time The fquare Root of that foutth Proportional
is the Space requit'd.
M.Mariotte, e.gr. found, by various Experiments, that a ptetty flrong Wind moves 24 Feer in a Second of Time ; wherefore, if the Space which the Water, aded on by the fame Force as the Air, will defcribe in the fame time, be requk'd; then will c= 1, ^ = 24, b = 070 ; and we fhall find/= •/ C57<f : 97o) = jf .
3. The Velocity of Wind being given, to determine the frcjftire requir'd to produce that Velocity ; we have this
Rule :— The Space the Wind moves in one Second of
Time, is to the height a Fluid is to be rais'd in an empty Tube in order to have a Preffure capable of producing that Velocity ; in a Ratio compounded of the fpecific Gra- vity of the Fluid to that of the Air, and of quadruple the Altitude a Body defcends in the firft Second of Time, to the forefaid Space of the Air.
Suppofe, e.gr. the Space the Air moves in a Second, a = 24 Feet, or 288 Inches ; call the Altitude of the third k, and the Ratio of Mercury to Air b : c = 1 3 580 : r, d = 181 Inches ; x will be lefs than that Number by one' Line, or ,5r of an Inch. And hence we fee why a fmall, but
■The Wind, therefore, blowing over the Conti-
ur with it; and is therefore
Further, the Earth in Summer is warmer than Water
expos d to the fame Rays of the Sun Hence, as the,
Air partakes of the Heat of contiguous Bodies; that over the Earth in Summer will be warmer than that over the Water : Therefore the Wind, He.
After the like manner it is (hewn, that the Lmd-Winds
ate cold in Winter Hence we fee why hwi-Winds
make clear, cold Weather. See Weather.
Our Northerly and Southerly Winds, however, which are
commonly efteem'd theCaufes of cold and warm Weather
Mr. <Derham obferves, are really the Effea of the Cold*
■ Warmth of the Atmofphere. Hence it is, that wa
afterwards wheels about towards the Southerly Quarters, when the Sun has well warm'd the Air, and again in the cold Evening turns Northerly or Eaflerly.
For the manner wherein North- Eaflerly Winds contribute to Slights ; fee Blight.
For the Effeil of Winds on the Barometer, and thermo- meter ; fee Barometer and Thermometer.
Wind, in Navigation, is the fame Agitation of the Air confider'd as ferving for the Motion of Veffels on the Water. See Sailing.
The Winds are divided with refpea to the Points of the Hotizon from which they blow, into Cardinal and Colla- teral.
Cardinal Winds, are thofe blowing ftom the four Cardi- nal Points, Eaft, Weft, North, and South. See Car- dinal.
Collateral Winds, are the intermediate Winds between two Cardinal Winds— -The Number of thefe is infinite, as
fudd.n Change in the Barometer, ftould be follow'd'with the Points from which"theybioware'; TuT only a feS of v,olent Winds. See Barometer. them are confidec . d in Pr / ake .-
The Fotce or the Wind is determin d experimentally by "
a peculiar Machine, call'd an Anemometer, Wind Med- furer ; which being moved by means of Sails, like thofe of iWind-Alill, raifes a Weight, that, ftill the higher it is rais'd, receding further from the Centre of Motion^ by Hi- ding along an hollow Arm fitted on to the Axis of the
- - only a few of them have their diftinguilhing Names. See Collateral. The antient Greeks at firft only ufed the four Cardinal
ones ; at length, they took in four more Vitruvius
gives us a Table of twenty, befides the Cardinals, in ufe among the Romans.
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