THE EARTH 141 



ously seems to arise from the rarefaction of the air by the sun, as tneir 

 duration continues with its appearance, and alters when it goes down. 

 The sun, it is observed, equally diffusing his beams upon land ana 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, unfortunately, 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, tolera- 

 bly regular in their visitations, what shall we say to the winds of our 

 own climate, that are continually shifting, 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 den- 

 sity 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 pcwer- 

 fully on the parts of it that are adjacent, will drive them forward, 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 one hand ; so 

 will any accident, that contributes to lighten the air, produce it on the 

 other : for, a lighter air may be considered as a vacuity, into which 

 the neighbouring air will rush : and hence it happens, that when the 

 barometer marks a peculiar lightness in the air, it is no wonder that 

 it foretels a storm. 



The winds upon large waters are generally more regular than those 

 upon land. The wind at sea generally blows with an even steady 

 gale ; the wind at land puffs by intervals, increasing its strength, and 

 remitting it, without any apparent cause. This, in a great measure, 

 may be owing to the many mountains, towers, or trees, that it meets 

 in its way, all contributing either to turn it from its course, or inter 

 rupt its passage. 



The east wind blows more constantly than any other, and 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 frequently see the clouds move another. This is general- 

 ly the case before thunder ; for it is well known that the thunder-cloud 

 always moves against the wind : the cause of this surprising appear- 

 ance has hitherto remained a secret. From hence we may conclude, 

 that weathercocks only inform us of that current of the air, which is 

 near the surface of the earth ; but are often erroneous with regard tt 

 me upper regions, and, in fact, Derham has often found them erroneous 



* Button, voi. ii. p. 25 



