Rainfall in Forest Regions. 33 



produced more by the retardation of the air currents passing through 

 the trees, than by any direct upward deflection due to the vertical 

 surface exposed to the wind. 



It is pointed out that the Transvaal is under conditions different 

 from those in Silesia, and the effects of afforestation upon the rain- 

 fall there may not be the same as in Silesia, although there is no 

 reason to think that woodland exercises any direct influence other 

 than in the way of modifying temperature and pressure. 



It is urged that the conditions of exposure to the rain winds, 

 the hygrometric conditions during rainfall, the temperatures and 

 pressures during rain winds, etc., are details which must all be 

 recorded in connexion with the subject, before a complete study of 

 the problem can be undertaken, and it is suggested that woodland 

 further may have an effect upon the actual amount of moisture 

 present in the atmosphere. 



In this connexion, part of the rainfall of a country may be due 

 to local circulation of water between the earth and atmosphere, as 

 well as to the general circulation between the land and water sur- 

 faces of the globe. 



