234 WINDS; CLIMATE; 



thaws are brought by the south-west wind, that 

 they begin to take effect first in the high-lying 

 districts. 



From the greater speed of the wind in the higher 

 regions there results a diminution of the density, 

 and, therefore, of the downward pressure of the 

 air, for the same reason that in swift rivers and 

 brooks the surface of the water sinks slightly from 

 the banks to the line of quickest flow. One 

 immediate and constant result, therefore, of strong 

 currents in the upper regions of the air, by reason of 

 the constant endeavour to maintain the balance of 

 forces, is the sucking or lifting up of the lower 

 layers of the atmosphere. 



It is in consequence of this that we so often see 

 light particles of dust and water, whirled up from 

 the earth during high winds and storms. 



The winds are the most effective agents in 

 equalizing the temperature of the surface of the 

 earth. Wherever they come in contact with the 

 earth they take the temperature which they find 

 there, and carry it with them to other regions. 

 Thus the polar currents, the air that flows from 

 higher to lower latitudes, bring coolness to the 

 torrid zone, while the returning trade- winds, when 

 they come down to the earth again in higher lati- 

 tudes, set down there a part of the warmth which 

 they have brought from the hotter belt of the earth. 



