778 The Outline of Science 



winds are called Hie N.lv :iiul S.K. "t Hides." :ind are remarkahly 

 constant winds. \n\\ the air that has risen ill Ilie Kquator moves 

 out towards north or south nlxirc Ilic trade winds, and for the 

 rcMsnn ahove inentioned its direction becomes S.\\ T . or \.\V. 

 These upper winds .-ire kno\\n as Ilie "anti-trades," and they 

 descend slowly in the regions of the Tropics, where there exist 

 other helts of eoinparalive e:ilni called the "horse latitudes." To 

 the north of the Tropic of Cancer there is a main drift of surface 

 wind from the S.\Y., while in the Southern Hemisphere there 

 is a .similar surface current from ahoiil \Y.\.\Y. in the corre- 

 sponding region. In the upper air these directions heeome more 

 nearly westerly, ill the Southern Hemisphere these winds are 

 so \\ell established as to he known as the "roaring forties," hut 

 in the Northern Hemisphere they arc not so definite in direction. 

 This is due to the predominance of sea in the Southern lleini 

 sphere, whereas in the Northern one the land and sea areas are 

 more equally divided. As already mentioned, land and \\ater 

 surfaces hehave very differently under the inlluencc of the sun's 

 heat: land heeomes rapidly heated, and cools with great rapidity; 

 water is slow holh to gel healed and to lose its acquired heat. 

 In summer we find areas of high pressure and low temperature 

 over the oceans just north of the Tropic of Cancer and south of 

 the Tropic of Capricorn, while areas of low pressure and high 

 temperature exist over the great continents. When winter comes 

 the high pressure with intense cold is found on the continents, 

 while the sea is now the region of warmth and low pressure. 

 These seasonal variations are much more strongly marked in the 

 Northern Hemisphere than in the Southern one. 



5 



The Indian "Monsoon" 



One very important clVecl of the seasonal change is to hr 

 seen in the "monsoon" which occur* with wonderful regularity 



