296 EVAPORATION AND CONDENSATION. 



There is nothing more admirable in the great 

 drama of Nature than the process of evaporation 

 and condensation, by which all the lakes, rivers, 

 and fountains of the earth are elevated from the 

 ocean ; transported over continents and islands ; 

 attracted by mountains ; precipitated by polar 

 currents ; and distributed in fertilizing showers 

 to cheer the thirsty lands. Vapour is condensed 

 by cold and lofty mountains, for the same reason 

 that it collects in drops on the sides of bottles 

 filled with cold water on a summer's day. 



Notwithstanding the greater amount of evapo- 

 ration and rain in the tropical than higher lati- 

 tudes, the atmosphere is more transparent, and 

 there are more clear days in the equatorial 

 regions ; and more during summer than winter 

 in temperate climates. 



According to the estimate of La Cotte, which 

 may be regarded as an approximation to the 

 truth, the average number of rainy days between 

 Lat. 12 and 60 N. are in the following ratios : 



N. 



From Lat. 12 to 43 78 days 



43 to 46 103 



46 to 50 134 



50 to 60 160 



It is therefore evident that the transparency of 

 the atmosphere, other things being equal, is in 

 proportion to temperature, which diminishes 

 from the equator to the poles. It is also known 



