g6 SCIENCE IN AFRICA 



The study of secular variation of rainfall is carried much further 

 by Schumann and Thompson (1934) who have analysed all useful 

 data in the Union, dividing the territory into thirty-two rainfall 

 districts. By the use of smoothed curves they have revealed more 

 or less pronounced secular variations during the period of about 

 fifty-five years for which records exist. Their conclusions are of 

 great importance in relation to the alleged desiccation of Southern 

 Africa and are considered in detail below. 



In the western part of the Cape, there is a section with winter 

 rains, one with summer rains, and one with rain at all seasons. 

 The rainfall (Plummer 1932) is extraordinarily variable not only 

 from year to year, but also from place to place, both the wettest 

 and driest spots in the Union occurring in this province. In the 

 Cape Peninsula great variations in the average rainfall within 

 short distances are brought about by contrasts between tlie warm 

 water of False Bay and the cold water of the open Atlantic in 

 relation to the prevailing winds and relief of the land. Even within 

 the limits of Capetown District variability is pronounced, though 

 the average rainfall of the city as a whole is about the same as that 

 of London and is just as reliable from year to year. The more 

 northerly parts of the Union, especially the Transvaal (Plummer 

 1926) and the Orange Free State, are intensely hot in summer and 

 subject to a somewhat unfavourable seasonal regime of rainfall, a 

 large part of it falling in thunderstorms which are probably the 

 worst in the world. Hail is a great scourge, stones varying in size 

 from walnuts to cricket balls being quite common, with deadly 

 effect on livestock. 



All parts of the Union which lie at any altitude experience from 

 time to time heavy falls of snow. In Basutoland, where there are 

 extensive tracts of country over 6,000 feet, snow may fall even in 

 summer. During the heat of summer low pressure over the interior 

 of South Africa causes a reinforcement of the moisture-laden south- 

 east trade wind from the Indian Ocean, and where this moist 

 wind strikes the high Drakensberg scarp heavy rain results. 



In South-West Africa there is an official Meteorological Office at 

 Windhoek created by the German administration. Little work is 

 now undertaken beyond the collection and summarizing of mete- 

 orological data. In this respect a good start was made by the 



