THE EARTH 



103 



vail, (and they are very common,) the in- 

 habitants enjoy a share of health and hap- 

 piness, unknown to those that live much far- 

 ther up the country, or such as live in similar j 

 latitudes without this advantage. The cause | 

 of these obviously seems to arise from the . 

 rarefaction of the air by the sun, as their ! 

 duration continues with its appearance, and I 

 alters when it goes down. The sun, it is ob- 

 served, equally diffusing his beams upon land 

 and sea, the land, being a more solid body 

 than the water, receives a greater quantity 

 of heat, and reflects it more strongly. Being 

 thus, therefore, heated to a greater degree 

 than the waters, it, of consequence, drives 

 the air from land out to sea: but, its influence 

 being removed, the air returns to fill up the 

 former vacuity. Such is the usual method 

 of accounting for this phenomenon; but, un- 

 r ortunately, these sea and land-breezes are 

 visitants that come at all hours. On the 

 coasts of Malabar," the land-breezes begin 

 at midnight, and continue till noon; then the 

 sea-breezes take their turn, and continue till 

 midnight. While, again, at Congo, the land- 

 breezes begin at five, and continue till nine 

 the next day. 



But, if the cause of these be so inscrutable, 

 that are, as we see, tolerably regular in their 

 visitations, what shall we say to the winds 

 of our own climate, that are continually shift- 

 ing, and incapable of rest? Some general 

 causes may be assigned, which nothing but 

 particular experience can apply. And, in 

 the first place, it may be observed, that 

 clouds and heat, and, in short,whatever either 

 increases the density or the elasticity of the 

 air, in any one place, will produce a wind 

 there : for the increased activity of the air 

 thus pressing more powerfully on the parts 

 of it that are adjacent, will drive them for- 

 ward ; and thus go on, in a current, till the 

 whole comes to an equality. 



In this manner, as a denser air produces a 

 wind, on the one hand ; so will any accident, 

 that contributes to lighten the air, produce it 

 on the other : for, a lighter air may be con- 

 sidered as a vacuity into which the neigh- 

 bouring air will rush : and hence it happens, 

 that when the barometer marks a peculiar 



Buffon, vol. ii. p. 252. 



lightness in the air, it is no wonder that it 

 foretells a storm. 



The winds, upon large waters, are gene- 

 rally more regular than those upon land. 

 The wind at sea generally blows with an even 

 steady gale; the wind, at land, puff's by inter- 

 vals, increasing its strength, and remitting it, 

 without any apparent cause. This, in a great 

 measure, may be owing to the many moun 

 tains, towers, or trees, that it meets in its 

 way, all contributing either to turn it from 

 its course, or interrupt its passage. 



The east wind blows more constantly than 

 any other, arid for an obvious reason : all 

 other winds are, in some measure, deviations 

 from it, and partly may owe their origin 

 thereto. It is generally, likewise, the most 

 powerful, and for the same reason. 



There are often double currents of the air. 

 While the wind blows one way, we frequent- 

 ly see the clouds move another. This is ge- 

 nerally the case before thunder; for it is well 

 known that the thunder cloud always moves 

 against the wind: the cause of this surprising 

 appearance has hitherto remained a secret. 

 From hence we may conclude, that weather- 

 cocks only inform us of that current of the 

 air, which is near the surface of the earth ; 

 but are often erroneous with regard to the 

 upper regions ; and, in fact, Derham has 

 often found them erroneous. 



Winds are generally more powerful on 

 elevated situations than on the plain, because 

 their progress is interrupted by fewer ob- 

 stacles. In proportion as we ascend the 

 heights of a mountain, the violence of the 

 weather seems to increase, until we have got 

 above the region of storms, where all is 

 usually calm and serene. Sometimes, how- 

 ever, the storms rise even to the tops of the 

 highest mountains; as we learn from those 

 who have been on the Andes, and as we are 

 convinced by the deep snows that crown 

 even the highest. 



Winds blowing from the sea are generally 

 moister, and more attended with rains, than 

 those which blow over extensive tracts of 

 land: for the sea gives off more vapours to 

 the air, and these are rolled forward upon 

 land, by the winds blowing from thence. b Foi 



b Derham's Physico-Theol. 



