CHAPTER IX 



CLIMATES OF THE WORLD 



1 86. Configuration and Climate. In passing from the 

 theoretical system of atmospheric circulation sketched in 

 last chapter to the actual conditions of the atmosphere in 

 different parts of the world, the disturbing influence of the 

 land must be taken into account. The student should 

 therefore read 214 and Chapter XV. as far as it refers to 

 the configuration of the continents, and study Plate XL, as 

 well as the maps illustrating atmospheric conditions. Sur- 

 face winds are altered in their direction in a very marked 

 way by mountain ranges and the edges of plateaux. At 

 the same time, sloping land differs from level ground by 

 setting up a local vertical circulation, acting exactly as a 

 chimney does in increasing a draught. ' In hot climates 

 mountaineers find a strong wind sweeping up the slope by 

 day helping their ascent, and on the summit the ascending 

 air-current from opposite sides rises straight* up, and is often 

 strong enough to carry off hats and notebooks. At night 

 the effect is reversed, and strong winds blow down the 

 slopes. The same effects are produced in a more intense 

 degree in narrow steep mountain valleys, the furious day 

 and night winds of which make travelling difficult and 

 dangerous in some of the Himalayan passes. Experienced 

 hunters on the Rocky Mountains build their fires just below 

 their tent, knowing that the night-wind will carry the smoke 

 down the valley. In still winter weather the air, chilled as 

 a thin layer on mountain sides, grows dense as its tempera- 



