WIND. 



Upon this principle the numbers in the third cohimn are cal- 

 culated. The propofition upon which this column has been 

 formed feems to be, that the impulfe of a current of air, 

 flrikin^ perpendicularly upon a given furface, with a cer- 

 tain velocity, is equal to the weight of a column of air 

 which has that furface for its bafe, and for its height the 

 fpace through which a body muft. fall, in order to acquire 

 that velocity of the air. 



It is obferved, with regard to this table, that the evidence 

 for thofe numbers, where the velocity of the wind exceeds 

 fifty miles an hour, does not feem of equal authority with 

 that of thofe of fifty miles, or under. Phil. Tranf. vol. li. 

 p. 165. 



Dr. Hales found (Statical Eff. vol. ii. p. 326.) that 

 the air ruflied out of a pair of fmith's bellows, at the rate of 

 63.73 f*^^^ '" ^ fecond of time, when comprefled with a 

 force equal to the weight of one inch perpendicular depth 

 of mercury, lying on the whole upper furface of the bel- 

 lows. The velocity of the air, as it pafled out of the trunk 

 of his ventilators, was found to be at the rate of three thou- 

 fand feet in a minute ; which is at the rate of thirty-four 

 miles in an hour. Dr. Hales fays, that the velocity with 

 which impelled air paffes out at any orifice may be deter- 

 mined by hanging a light valve over the nofe of a bellows, 

 by phant leathern hinges, which will be much agitated and 

 lifted up from a perpendicular to a more than horizontal 

 pofition by the force of the rufhing air. There is another 

 more accurate way, he fays, of eftimating the velocity of 

 air, -viz. by holding the orifice of an inverted glafs fiphon 

 full of water, oppofite to the ftream of air, by which the 

 water will be deprefled in one leg, and raifed in the other, 

 in proportion to the force with which the water is impelled 

 by the air. Defcript. of Ventilators, 1743, p. 12, &c. 



The velocity and force of the wind are determined ex- 

 perimentally by a peculiar machine, called an anemometer 

 or ijjind-meaftirer. Of thefe there have been many, varioufly 

 conftrufted. See Anemometer, Anemoscope, and Wind- 

 Gage. 



Wind, Qualities and EffeRi of. I. " A wind blowing 

 from the fea is always moift ; in fumrher, it is cold ; and 

 in winter, warm, unlefs the fea be frozen up." This is 

 demonftrated thus : there is a vapour continually rifing 

 out of all water, (as appears even hence, that a quantity of 

 water, being left a little while in an open vefTel, is found 

 fenfibly diminiflied,) but efpecially if it be expofed to the 

 fun's rays ; in which cafe, the evaporation is beyond all 

 expeftation. By this means, the air incumbent on the fea 

 becomes impregnated with a quantity of vapour. But the 

 winds, blowing from off the fea, fweep thefe vapours along 

 with them ; and confequently they are always moiit. 



Again, water in fummer, &c. conceives lefs heat than 

 terreftrial bodies, expofed to the fame rays of the fun, do ; 

 but in winter, fea-water is warmer than the earth covered 

 with frofl and fnow, &c. Wherefore, as the air contiguous 

 to any body is found to partake of its heat and cold, the 

 air contiguous to fea-water will be warmer in winter, and 

 colder in fummer, than that contiguous to the earth. Or 

 thus : vapours raifed from water by the fun's warmth in 

 winter, are warmer than the air they rife in, (as appears 

 from the vapours condenfing, and becoming vifible, almoft 

 as foon as they are got out into air. ) Frefh quantities of 

 vapour, therefore, continually warming the atmofphere over 

 the fea, will raife its heat beyond that of air over the land. 

 Again, the fun's rays reflefted from the earth into the air, 

 in fummer, are much more than thofe from the water into 

 air : the air, therefore, over the earth, warmed by the re- 



fledtion of more rays than that over water, is warmer. 

 Hence, /ea-ivinds make thick, cloudy, hazy weather. 



2. " Winds, blowing from the continent, are always 

 dry ; in fummer, 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 fenfible, than thofe 

 from water. The wind, therefore, blowing over the conti- 

 nent, carries but httle vapour with it, and is therefore dry. 



Farther, the earth in fummer is warmer than water ex- 

 pofed to the fame rays of the fun. Hence, as the air 

 partakes of the heat of contiguous bodies, that over the 

 earth in fummer will be warmer than that over the water : 

 therefore, the winds, &c. 



After the like manner it is (hewn, that the land-winds are 

 cold in winter. Hence, we fee why land-winds make clear 

 cold weather. 



Our northerly and foutherly winds, however, which are 

 commonly efteemed the caufes of cold and warm weather. 

 Dr. Derham obferves, are really rather the effeft of the 

 cold or warmth of the atmofphere. Hence it is, that we 

 frequently fee a warm foutherly wind, on a fudden, changed 

 to the north, by the fall of fnow or hail ; and that in a 

 cold frofty morning, we fee the wind north, which after- 

 wards wheels about toward the foutherly quarter, when 

 the fun has well warmed the air ; and again, m the cold 

 evening, turns northerly, or eafterly. See Darwin's Obfer- 

 vationsyi/^ra. 



For the manner in which north-eafterly winds contribute 

 to blights, fee Blight. For the effeft of winds on the 

 barometer and thermometer, fee Barometer, &c. 



The utility of winds has been univerfally acknowledged. 

 The ancient Perfians, Phoenicians, Greeks, and Romans, 

 facrificed and erefted temples to the winds ; as we learn 

 from Voffms, Theolog. Gentil. lib. iii. part i. cap. i. 

 Befides their ufe in moving bellows, mills, and other ma- 

 chines, applied in various ways to the fervice of mankind, 

 and the benefits refulting from them to navigation and 

 trade, they ferve to purify and refrefh the air, to convey 

 the heat or cold of one region to another, to produce a 

 regular circulation of vapours from the ocean to countries 

 remote from it, and to fupply, by wafting them in their 

 progrefs againfl hills, &c. fprings and rivers. 



Wind has been, by many authors, made the bafis of many 

 different difeafes : among others, Dr. Reyn has given it as 

 his opinion, in a Treatife on the Gout (De Arthritid.), that 

 flatufes, or wind inclofed between the periodeum and the 

 bone, are the true caufe of that difeafe ; and accordingly, 

 that all the methods of cure ought to tend to the expelling 

 of that wind. 



He is alfo of opinion, that head-aches, palpitations of the 

 heart, tooth-ache, plturify, convulfions, colics, and many 

 other difeafes, are originally owing to the fame caufe, and 

 only differ in regard to the place affeAed, and to the various 

 motions and determinations of the wind. The moveablenefs 

 of the pain in gouty perfons from one part to another, he 

 looks on as a proof of this, and thinks that the curing of 

 the gout by burning moxa, or the cotton of the mugwort 

 leaves, upon it, is owing to its giving way to the wind in 

 the part to evaporate itfelf. 



That thefe winds are cold, appears from the fliivering fits 

 which generally precede a paroxyfm of the gout ; and that 

 the fhiverings in the beginning of fevers, and before all 

 fits of agues, are owing to the fame caufe, is fuppofed by 



tkis 



