110 FOREST INFLUENCES. 



amount under trees is greater than that outside, there is a fair pre- 

 sumption that the rainfall over the trees is persistently heavier, and 

 where this is found for several months, and in the warm season when 

 the precipitation is rain and can not be very long sustained in the 

 foliage, the presumption becomes very much stronger. There were a 

 good many cases in the two hundred years of observation at the Ger- 

 man stations when the monthly catch under woods was greater than in 

 the open fields. 1 will take a few of the most interesting, for the Avarm 

 season : 



Carlsbcrg, May, 1881 (1.24), and September (1.11); also September, 1885 (1.20), 

 June, 1887 (1.20), and May, 1888 (l.U); Scliou, May to September, 1886 (1.05, 1.00; 

 1.04, 1.40, 1.40). 



These are both stations among evergreens, and the summer reduction 

 of the catch under trees for this season, for the German stations, is .20 

 per cent. If this is added to the above they become — 



For Carlsberg 1.50, 1.37, 1.46, 1.46, 1.40 



For Schoo 1.31, 1.26, 1.30, 1.66, 1.66 



and it appears that the monthly fall in the w(«)ds may be from a fourth 

 to two thirds more than in adjacent fields. If instead of the .20 per 

 cent of the German service, the .45 per cent found by Fautrat, by actual 

 measurement, as the difference in rainfall above and below evergreens, 

 be added, these values become .19 per cent greater, and the rainfall 

 observations at the forest stations generally become larger than those 

 in open fields. 



But Fautrat's .31 per cent for deciduous trees and .45 per cent for ever- 

 greens are the results of brief series of observations at only two sta- 

 tions and can not be extended to the results of observations at other 

 stations without uncertainty. 



They aflbrd, however, some grounds for the ijresumption that rainfall 

 is heavier over woods, and it is not hard to find reasons why it shonld 

 be. But it is most satisfactory to wait until the fact has been proven 

 beyond a doubt, and in the lack of sufficient observations on this point 

 lies the chief and most important gap in forest meteorological work. 

 For the completion of the theory of the action of forests on climate 

 exact observations are needed above trees at many stations and for 

 long series of years, and the most'imiiortant data to be obtained are 

 those relating to precipitation. The rainfall* caught under trees is of 

 minor importance — far subordinate to the amount caught above trees. 



