250 RESULTS OF COMPARATIVE OBSERVATIONS: BAVARIA. 



From woods without litter, about 21,780 cubic feet = 1,301,250 pounds = 

 G80.6 tons. 



From woods with litter, about 8,700 cubic feet = 544,495 pouuds = 

 272 2 tons. 



The preceding figures, which express the mean of all observations, 

 and the influence of the forests in the whole, will vary of course in dif- 

 ferent places, according to extent of forest, its location, kind of timber, 

 and other circiimstances. It will, however, be found in all cases that 

 the influence of the forest on the evaporation of water is greater than 

 on the temperature of the air, and it is aftected chiefly by the greater 

 or less movement of the air. Daily experience shows that currents of 

 air will increase evaporation, and dry winds more than ihose that are 

 moist. It may be considerable even with a very low temperature, iu a 

 dry, strong wind. 



Relation of the evaporation from a wooded and unicooded soil ; or the injiv^ 

 enee of the forest on the evaporation of ivater in the soil. 



Having shown the differences of evaporation from a free water surface, 

 the question follows, as to how far the presence or absence of woodlands 

 may affect the evaporation from the soil. There is no more important 

 question in the climatology of forests. The results^of only the tull years 

 1869 and 1870 are available for the study of this question, and the 

 average mean of these years shows that Irom a Paris square foot of 

 soil half a foot deep, saturated with water by capillary attraction, the 

 following results w^ere obtained : 



* Thp.se observations can only be made from April to October, becanso freezing interrupts the work- 

 ins: of the apparatn.s. 



Tf'o tignr. s in this table are from the means as given on pages 204 and 206 of the_tabular portion of 

 Dr. Ebermayer's work. 



The effect of rains and S7iou's upon the moisture of the soil. 



Of the rain and snow that fall upon the earth, a part runs off on the 

 slopes of the surface ; another part evainorates, and a parr penetrates 

 into the earth and is distributed in all directions by c ipillaiity and hy- 

 drostatic pressure. Some of the latter is retained in the pores of the 



