60 PEESIDEMIAL ADDRESS SECTION C. 



This is repeated time after time, until the tops of the 

 ]iiountaiii!5 are reached, which, being cold and rarefied, can 

 produce rain from a lesser actual humidity than happens lower. 

 This accounts for the frequent short rains, the mists and the 

 moisture, wliich alternate rapidly with drier intervals on the 

 mountains, but which give rise to all rivers or springs rising- 

 and flowing steadily in these elevated localities. On crossing- 

 the range and descending the other side, or if by chance the 

 descent is made on the same side, climate becomes warmer 

 and pressure greater as altitude is lost, and the atmosphere 

 then is able to carry all the moisture it has broug-ht over the 

 ridge or brought down from the mountain top, unless it 

 hapxiens to encounter a cold current or be driven high enough 

 to again reach saturation, in which case the raindrops or hail- 

 crystals may be formed at a high enough elevation to fall 

 with considerable A'elocity to the ground. 



We already have proved that moisture transpired is 

 moisture saved and banked in the atmosphere. With the 

 foregoing explanation we are now able to see that the more 

 actual moisture there is in the atmosphere, the sooner will 

 saturation be reached at any point, and also the more flow will 

 there be in the overberg rivers and the higher relative 

 humidity in the general atmosphere overberg. That relative 

 humidity may not allow of precipitation as rain, but it 

 produces a less arid atmosphere — one in which plants can 

 live and dew can be formed, a condition whicdi allows of dry- 

 land farming where without that moisture cultivation without 

 irrigation is impossible. We see much of this in the country 

 west of the Maluties. 



This atmospheric condition also makes possible the 

 continuous drizzle rains, which do so much more good, and 

 leave so much more soaked in, than the storm-showers which 

 give a deluge for a few minutes, most of which goes off as 

 flood and is lost for ever. Three inches of rain drizzled during 

 three days gives practically no off-flow from good grass-veld 

 or forest, but three inches of rain falling as a deluge during 

 an hour on eroded Karroo does much immediate flood-harm and 

 no permanent good. 



A Dry-Blanket. 

 Even between the Indian Ocean and the mountains, 

 although there are several steps Avhich intercept clouds and 

 so form sour-veld mist belts, the intervening thorn-veld flats 

 and valleys are so protected by a " dry-blanket " (i.e., an 

 atmosphere in which pressure and temperature are sufficient to 

 carry much moisture without reaching saturation) that less 

 rain falls- tliere than on the mountain slopes, and more or less 

 arid conditions prevail, which causes the flora to be either 

 xerophytic or to wilt, since though vegetation transpires 

 freely the supply of moisture from the soil is small or spasmodic. 

 As in all climatic variations, the extremes kill. It is the 

 occasional extreme drought or ariditv which controls the flora 

 here, in so far as that is not controlled by fire. Burned veld 

 naturallv increases the local aridity, as well as that of all 



