UPPER INDIA. D 



of cooler denser air, to displace the lighter heated air, creates 

 a large indraught, or, in other words, constitutes a wind. 



The alternations of sea and land breezes which daily occur 

 on the seashore, more particularly in tropical climates, and 

 which moderate the heat of the climate, are an apt illustration 

 of the influence of the sun in causing wind. As the land be- 

 comes heated with the rays of the sun, the air hanging over 

 it becomes heated, and a rush of cooler air from the sea the 

 sea-breeze takes place, which displaces the air heated by 

 contact with the land, which rises. At night, on the contrary, 

 as the land cools by radiation, the air in contact with it 

 becomes cooler and heavier, and, by its greater specific 

 gravity, sinks down to, and spreads over the sea, the water 

 of which is not cooled by radiation to the same extent as the 

 land, and displaces the warmer air resting on its surface. 

 This is the land-breeze. The sea-breeze should, according to 

 this theory, be stronger on the shore of a bare stony country, 

 and the land-breeze stronger on the shore of a country well 

 covered with vegetation. Whether such has, by observation, 

 been found to be the case, I do not know. 



The air of a country is not heated to any extent by the 

 passage of the rays of solar heat through it, but by their 

 coming in contact with the surface of the land, or objects on it. 

 The air obtains its heat from contact with heated objects, the 

 chief of which is the surface of the land ; and is never so hot in 

 the hottest days as the object from which it obtains its heat. 



As the earth revolves on its axis, the eastern parts of a 

 country are first presented to the influence of, and are heated 

 by the rays of the sun. The air in contact with the soil will 

 become heated and lighter, and cooler, denser air will, from 

 its greater specific gravity, rush in and displace it, and cause 

 it to ascend. As the land further to the west has been some- 

 what cooled down by radiation and the absence of solar heat 



