306 EFFECTS OF E0EEST8 ON RAINFALL. 



So far as my own observations have gone it is in accordance with 

 what has now been advanced. My observations have been made 

 incidentally and not of purpose, and they are general rather than 

 precise. They have been made, one class of them in Scotland, the 

 other in Africa, or countries which are in very different climatal condi- 

 tions, and for this it maybe considered by some that some allowance 

 should be made; but such as they are they are these : While.the genial 

 shower or the drizzling mist appears to be a characteristic of wood- 

 land rain, deluges of rain like thunder plumps are the forma which I 

 have found most characteristic of rain in the arid regions of South 

 Africa ; frequent showers and constant damp in spring and autumn 

 and winter alike are characteristic of woodlands in Britain with which 

 I am familiar, a cloudless sky, and a persistent drought broken only 

 by an occasional deluge, brief in its duration and local in its range, 

 are the characteristics of the other. In the one we have the rainfall 

 distributed over eight or ten months of the year, with occasional 

 showers in the course of the intervening summer ; in the other a 

 drought continued for months, or it may be for years, and a rainfall 

 of two days or three, or of some hours, or it may be of half an hour at 

 most. In the one we may have the rainfall distributed over the whole 

 of the area of a hundred or a thousand square miles, falling not over 

 the whole simultaneously or continuously, but so distributed in time 

 as well as in space that no part suffers lack ; in the other we may 

 have a deluge of rain over twenty square miles at one time within an 

 area of a thousand, and a deluge over other twenty square miles 

 at another time, weeks or months, or it may be years thereafter. 



The geographical distribution of rain may be attributable to geo- 

 graphical position and contour of the country. Such deluges of rain 

 as have now been referred to may be attributable in some cases- to 

 eddies in one or other of the aerial currents flowing continuously be- 

 tween the equator and the poles ; in other cases to the passage of 

 a minor cyclone or whirlwind above the place ; but the frequent 

 drizzling genial showers prevailing in a wooded country may be con- 

 sidered a form given to the rainfall in some measure by an influence 

 of the woods ; and the absence of these in arid woodless regions, in 

 which the mean annual rainfall is the same and the conditions similar, 

 may be considered in a corresponding manner attributable to the 

 absence of forests. 



