132 



The Realm of Nature 



CHAP. 



ture falls, and flows gently down into the valleys, filling them 

 to a certain level with intensely cold air. The peasants in 

 many valleys of the Alps perch their wooden cottages on 

 knolls or rocks, not so much for the picturesqueness of the 

 site, but in order to stand above the surface of the flood of 

 icy air which streams through the valley in winter. Rain- 

 fall is still more intimately connected with configuration. 

 Meteorologists, in speaking of the climate of a place, mean 

 the average state of the atmosphere with regard to warmth, 

 wind, rain, and all other variable conditions. 



187. Atmospheric Temperature in different latitudes. 

 The excess of land in the northern hemisphere, compared 



with the southern, alters the distribution of the solar energy 

 shed equally on both, and prevents the simple astronomical 

 climate zones ( 125) from corresponding on the two sides 

 of the equator. Fig. 27 shows by means of curves the 

 mean temperature of the year, as calculated by Professor 

 Ferrel for each 10 of latitude from 80 N. to 60 S. 

 Latitude is marked along the top and temperature up 

 the side of the diagram, the three curves of which cor- 



