5G PEKSIDKNTIAL ADJJKKSS SKCTIOX C. 



rapid floods to the ocean, and only a small portion of it soaked 

 in to form a reserve for the next ten j^ears to draw upon. 

 Also it is to be expected that after the few rainfall cycle 

 3'ears just mentioned, another long^ period will occur before the 

 portions of South Africa fed by the south-east winds will be 

 well supplied again, the cycles g-ettino- g-radually better 

 distributed thereafter. 



That the South African records are insufficient as a basis 

 on which to frame or to condemn cycles suspected to be at 

 work locally is admitted, especially as tlie summer rainfall 

 records are all upset hj being divided into calendar years 

 instead of into seasonal years, but that is no proof that cosmic 

 cycle causes known elsewhere are not active here also ; all 

 that is required is that we study and recognise what is going 

 on around us. 



I trust, liowever, that I liave made clear how it happens 

 that periods of heavy rainfall alternate in cycles, with periods 

 of intense drought and desiccation ; that these cycles are of 

 more or less irregular duration between seven and seventeen 

 years, with average of eleven years : that other cycles of shorter 

 duration are concurrent, but of different average j)eriods and 

 acting differently and in different localities ; that when these 

 different cycles happen to overlap, the effect is increased in 

 each direction; and that all these cycles are quite beyond man's 

 power of control. 



It is held by some that, if such be tlie case, it is beyond 

 the power of man to influence in any way the rainfall which 

 nature, through sunspot and other cycles, baric migrations, 

 day and night breezes, and other means, arranges for South 

 Africa; in other words, that wliat is predestined will happen, 

 and that what is lifted by evaporation from tlie ocean, whether 

 that quantity be large or small, is what we have to be satisfied 

 with and what we have to take as it comes. That, however, 

 overlooks the fact that the same moisture is often precipitated 

 more than once; that all moisture, either evaporated from the 

 earth's surface or transpired by plants, is then available in 

 the atmosphere to fall again as rain or dew; and that the 

 amount either evapoiated or transpired is largely regulated by 

 the vegetation covering the earth. Where there is a dense 

 grass-sward, or a forest liumus-bed covered by a forest canoDV, 

 nearly the whole rainfall is retained until it either sinks into 

 the subsoil, is slowly evaporated, or else is used by the vegeta- 

 tion and again transpired. Where there is little or no 

 vegetation the surface is usually baked hard, rapid infiltration 

 of rain-water into the soil is impossible, and the result is that 

 almost all the rain that falls there rushes down some river to 

 the sea, caiTying soil along with it and producing erosion 

 which in time becomes serious, and not only carries away the 

 flood-water, but also drains away whatever moisture may find 

 its way into the soil and subsoil. It is in tliis connection that 

 man's influence is greatest. 



By grass burning he produces a condition of no vegeta- 

 tion, so for months there is no shade, and for a year at least 

 there is no humus, and, consequently, when rain does fall 



