RESULTS OF COMPARATIVE OBSERVATIONS : BAVARIA. 243 

 Evaporation at different seasons, in culic contents and depths. 



Difference of evaporation in open fields and in woodlands at different seasons. 



The evaporation is, therefore, four times as great in summer as in 

 winter. Nothing could give us a clearer idea of the influence of wood- 

 lauds upon the evaporation of water than the above figures. 



Clearings must, therefore, accelerate evaporation in a high degree, 

 particularly in summer, and most in warm seasons and climates, and 

 from these facts alone we can see the great imi)ortance of the forests in 

 retaining the moisture of the earth and the abundance of springs dur- 

 ing the warm season. A closer examination of the above figures shows 

 further the interesting result that the evaporation of water in tlie forest^ 

 at all seasons, is about C3 per cent, less than in the open fields. This is 

 much more surprising, as we have hitherto shown that the mean temper- 

 ature of the air in the forest, in the annual result, is but little below that 

 of the fields, so that if this evaporation depended solely upon the tem- 

 perature of the air it could have but slight influence, especially in the 

 winter mouths. But as, in fact, we find the relative influence in winter 

 almost as great as in summer, it follows that the amount and rapidity 

 of evaporation depend a great deal more upon the motion of the air 

 than upon the temperature. 



The evaporation of water in the soil depends upon the same factors 

 as tho.se of a free water surface, and takes place generally in accordance 

 with the same laws. If the process goes on faster or slower, it will be 

 found to depend upon the formation of the soil, the degree of looseness, 

 the kind of covering, location, and force and direction of the wind. 

 In these experiments the soil was always saturated with water by 

 capillary attraction, so that only the larger spaces contained air. Jt was 

 not attempted to ascertain the evaporating power of different kinds ot 

 soil under circumstances otherwise similar, but merely to find the in- 

 fluence of the forest and tJhe litter strewn upon its surface upon the 



