RELATION OF EVAPORATION TO FORESTS. 



99 



Dr. Ebermayer's series of observations incladedinore elaborate ones 

 ou evaiioratioii tlum those of the German service. In addition to the 

 evaporation from a water surface he also measnred tliat from bare soil 

 ontside the forest and within, and that from soil in the forest which 

 was covered by forest litter. The latter observations were made only 

 in the months from April to October. His instrnments were first a 

 simple one, somewhat like that of the German service already described, 

 and then the evaporometer of Lainont. The evaporation from earth, 

 either naked or covered with litter, was measured by an apparatus 

 which worked on the x)rinciple of the student lamp and Icept the earth 

 always saturated. The vessel containing the earth is of zinc. The 

 instruments are protected from the sun, rain, and snow, but the air is 

 given free access to them. The following table gives the percentages 

 which are derived from his results, with some corresponding ones from 

 the German stations to permit comparison. The evapf)ration from a 

 water surface is the mean for six stations for three years ; the other evapo- 

 ration percentages are for two, Avith the exception of two months. The 

 precipitation is for one year. Thepercentages are always made from the 

 averages for corresponding years. The data from the German observa- 

 tions are for ten years. 



Evaporation in xooods in per cent of evaporation in the open. 



This table brings to light several interesting facts. The ratio of 

 evaporation without and within woods is about the same in the two 

 services, giving confidence to the generality of these figures. It ap- 

 pears, however, that the eva])oration from a bare soil is about the same 

 as that from a water surface. This is very large and is probably due 

 to the fact that tlie soil is always kept saturated. The ratio between 

 evaporation from bare soil within woods and without is about the same 

 as that for the water surface. 



The most striking feature of the table is the eftect of the presence of 

 forest litter on the evaporation from tlie soil within Ibrests. The char- 

 acter and depth of tliis litter would make nuich dilVerence, and it was 

 probably kept as nearly as possible like that lying naturally in undis- 

 turbed woods. In this series of observations, even with saturated soil 



