208 EFFECTS OF FORESTS ON SPRINGS AND RIVERS. 



" Far more important, however, than the thermal eflfects upon the 

 soil and the atmosphere are the influences inherent to the forests of a 

 country which affect the humidity of the soil and air, the quantity of 

 the rainfall, and the abundance of the springs. In relation to these 

 points the investigations of Ebermayer have produced very valuable 

 results. 



" In the fii'st place, it has been discovered that the influence of 

 forest-lands upon the absolute contents of moisture in the atmosphere 

 — the evaporation pressure — cannot be proved, in spite of the fact 

 that the air of the woods is always more humid, relatively, than the 

 air of the open grounds. This is easily explained by the greater cool- 

 ness of the former. The higher a place is situated, the more marked 

 was the relative difference observed in Bavaria between the humidity 

 of the wooded and imwooded country. Ebermayer assumes that the 

 augmentation of aqueous descents, caused by a larger area of wood- 

 land, noticed at many places, is to be attributed merely to the 

 increase of the relative moisture within the forests. 



" In close connection with the relative humidity of the atmosphere 

 of wooded and unwooded lands stands the quantity of water which 

 has been discovered to evaporate at given points, during a given 

 interval of time, at a certain temperature, and at a certain pressui'e 

 of the atmosphere, from an open surface of water. 



" The Bavarian observations have proved that in an average of one 

 year less than 64 per cent, of water evaporates within the forest than 

 outside of it. The fact is more remarkable, because the proportion of 

 evaporation was nearly the same at all seasons of the year, although 

 the temperature of the atmosphere of the forests and the open lands 

 is so different in the winter from what it is in summer. This forces 

 us to the conclusion that the movement of the air, which is very much 

 less within the woods than outside of them, plays a far more 

 important part in relation to evaporation than has hitherto been 



" But for the abundance of water and the forming of springs in any 

 country, the evaporation from rivers, ponds, and lakes is not so impor- 

 tant, by any means, as the evaporation of the water of the soil. 



" The amount of evaporation from one square foot (Parisian 

 measurement) of an open surface show, in Parisian cubic inches, as 

 follows : — 



