riEPORT P.Y Af'APKMY OF SCFKNOE OF VIENNA. 201 



the exposure of the mstruments, they being in some places exposed 

 to the sunshine and the rain, in others protected from these, by 

 difference in the sizes of the atmometers, and by difference in the 

 materials of which these are made, — it is not impossible, from these 

 causes, that an atmometer of small size, made of metal, and set in 

 the sunshine, may give an annual evaporation which exceeds by far 

 say two or three times, the amount of the rainfall. 



" In consequence of the difl&culty of determining by direct observa- 

 tion on evaporation the evaporation from the gi'ound, and thereby 

 determining the quantity of the rainfall available for feeding springs 

 and streams, some have sought to determine this directly in part 

 by comparison between the quantity of water delivered by a river 

 in the course of the year, and the rainfall on the whole valley drained 

 by it; or, otherwise, between the quantity of water percolating through 

 a given section and the rainfall over a given range, 



" If now there be also in a wood a considerable portion of the 

 rainfall kept by the twigs and leaves from immediately reaching the 

 ground, the difference between that rainfall and the evaporation 

 (amounting, according to Ebermayer, to 72 per cent., Zeit&chrift fxir 

 Met. viii. 274) will also be retained longer in the forest and get time 

 to permeate and feed the springs. 



" The remainder of what has not been dispersed by evaporation 

 either penetrates the ground or flows away over the surface. 



" In the former case it seems principally to feed the springs; in the 

 latter case it is carried directly to the water-courses, and after a brief 

 time produces a more or less considerable flooding of these. 



" It is generally acknowledged that the forest, through the vegeta- 

 tion of lichens, mosses, &c., peculiar to it, is pre-eminently fitted to 

 absorb the rain, to store up the same, and only gradually — little by 

 little — to yield it again. 



" In view of this, the aforementioned investigations in regard to the 

 quantity of water which sinks into the ground to certain depths is 

 very instructive, as they give on the one hand the relative effect of 

 different kinds of soil on the absorption of the different plants with 

 which they are covered, and on the other the proportion of the 

 moisture absorbed by the soil in the course of the year. It appears, 

 according to the latest of these, that the absorption of the forest is 

 especially manifested in the warm season of the year.* 



" In regard to that portion of the rainfall which does not penetrate 



* According to Ebermayer, in the summer the following per centages of the rain- 

 fall was fovind at the depth of one metre ;— 



X 



