Periodical Literature 149 



perature, exerts a marked influence on the rainfall ; into most 

 data upon the basis of which our problem will be answered, altitude 

 will enter to a greater or less degree. 



Recent studies in Silesia by Schubert indicate the precipitation 

 in millimeters varying with forest cover and altitude as 

 529+o.78/>+o.57a, that is, precipitation varies above a constant 

 amount by 0.78 mm. for each per cent, of the surface of the 

 country under forest cover and 0.57 vim. for each meter in alti- 

 tude. 



However, beyond about 50 per cent of the total area forest 

 cover seems to exert little additional influence upon the rainfall, 

 so that for the conditions in Silesia with about 660 mm. rainfall 

 and 29 per cent, forest cover, complete deforestation would 

 reduce this amount by but 5 per cent., and 20 to 80 per cent 

 additional forest cover would raise it by but i per cent. 



The assumption is made that one-half the increased amount 

 registered by a rain gauge within the forest as compared with 

 one in the open is due to the difference in exposure to winds. 

 Another series of data from a particular area, averaged for four 

 years, indicated a variation between 600 and 650 mm ; agreeing 

 closely with the formula. Crediting one-half of this to wind we 

 have a forest cover exerting an influence equal to that of an ele- 

 vation of 40 meters. 



Wald und Niederschlag in Schlesien. Zeitschrift fiir Forst. iind Jagd- 

 wesen. June, 1905. Pp. 375-380. 



Take the topmost whorl of a young spruce, 



Simple cutting off the stem 2 inches below and 



Hygrometer. above the whorl, remove all the branches 



except one good straight one and bark both 

 stem and branch. Nail this tight to a wall through the stem, so 

 that the branch lies flat against the wall, and its height can be 

 marked. Its position will vary with the humidity, being higher 

 in wet, lower in dry weather. The arcs which it describes can 

 after some experience be graduated and the humidity expressed 

 in per cent. This behavior of the branch is supposed to be also 

 of benefit to the living plant in directing the run off of rain 

 toward the stem and in dry hot weather reducing transpiration, 

 by change of position toward the sun. 



Note in Centralblatt fiir das gesammte Forstwesen, Feb. 1906, p. 95. 



