122 THE OCEAN 



014 inch. The air filling the central portions 

 of the anticyclones is relatively immobile, and 

 probably contains fewer dust particles than 

 elsewhere ; it will therefore be less cooled 

 by nocturnal radiation and less heated by 

 solar radiation, and the change of the aqueous 

 vapour from the gaseous to the liquid state 

 and vice versa will also be less than elsewhere. 



The effect of the earth's rotation on a body 

 moving on its surface is to cause it to deviate 

 towards the right in the northern hemisphere 

 and towards the left in the southern hemi- 

 sphere. The winds are therefore deflected, the 

 trade- winds in the northern hemisphere blow- 

 ing equatorwards from the north-east, and in 

 the southern hemisphere from the south-east, 

 while the winds blowing polewards from the 

 anticyclonic areas of temperate regions become 

 westerly winds in both the northern and 

 southern hemispheres. 



The alternate heating and cooling of the 

 continental masses in summer and winter 

 result in the formation of regions of low pres- 

 sure in summer and of high pressure in winter 

 over the interior of great continents. In the 

 northern summer over the interior of Asia the 

 pressure is low (cyclonic) and winds blow in 

 from the surrounding oceans ; the south-east 

 trade-wind of the Indian Ocean is thus 

 deflected and becomes a south-west wind 



