The Phenomena of the Atmosphere. 85 



or wherever there is a large fire. A current of 

 air is also to be perceived rushing through the 

 key-hole, or any chink or crevice, into a heated 

 room. This may serve to give a general idea of 

 the causes of winds. 



This principle we consequently find realised 

 on a great scale, in what are called the trade 

 winds, which blow constantly from east to west 

 near the equator. When the sun shines intensely 

 upon any part of the earth, it is plain that, by the 

 immense accession of heat, the air must be greatly 

 rarefied. The cold air will therefore rush from 

 the adjacent parts to that where there is little 

 resistance, and consequently cause a stream or 

 current of air, in other words, a wind, towards 

 that quarter. The sun rises in the east, and sets 

 in the west, consequently the air will be heated 

 gradually from east to west, and the wind will 

 blow in that direction. Near the equator, there- 

 fore, where the surface of the earth is heated in 

 succession from east to west, there will be a 

 constant wind from the east, but on the north 

 side of the line it will incline a little to the north, 

 and on the south side a little to the south, for an 

 obvious reason, because it is colder towards each 

 pole, and therefore the mass of cool air will be 

 principally drawn from these quarters. 



The same cause will explain, in a popular way, 

 the land and sea breezes in the tropical climates. 

 In islands, and small tracts of land which run into 

 the sea in those regions, it will generally be found 



