100 SCIENCE IN AFRICA 



for Uganda and Kenya, Rodwell Jones (1933) for Kenya, Hurst 

 and Phillips (1933) for all the regions lying within the Nile Basin, 

 Sir Henry Lyons (191 7) and Paap (1934) for the former territory 

 of German East Africa (Tanganyika and Ruanda-Urundi). There 

 are still large areas, such as the northern arid regions of Kenya, 

 where information is scanty. The meteorology of these countries 

 is exceptionally interesting on account of the local complexities 

 introduced by such impressive natural features as the rift valleys, 

 the equatorial snow peaks, and the great lakes. The investiga- 

 tions of Dr. Brooks and others on the rainfall of British East 

 Africa show that this is governed to a much greater extent by 

 vertical relief than might perhaps have been expected near the 

 equator where the rains are mostly of the doldrum type without 

 much wdnd. In England we are accustomed to associate 'oro- 

 graphic' rainfall with the effects of mountain slopes in forcing 

 upwards damp cyclonic winds, condensation resulting from cooling 

 by adiabatic expansion as the air rises into levels of reduced pres- 

 sure. This effect undoubtedly occurs also in East Africa, as is 

 shown by the considerable precipitation which occurs on the rising 

 ground exposed to the south-east monsoon. But mountains also 

 increase rainfall by hindering the free passage of rain-bearing cur- 

 rents of air, so that rains last longer than in open plains, and also 

 by favouring local thunderstorms. The latter factor is apparently 

 of great importance in the tropics. 



Nyasaland has its own service under the Department of Agricul- 

 ture. Two rainfall maps of the w^hole territory, for November to 

 April (wet season) and May to November (dry season), have been 

 compiled by Hornby (1935) and the climate of Central Nyasaland 

 has been described by Hornby (1933). 



The whole East African region, where meteorology is intimately 

 bound up with hydrology, is of the greatest scientific interest, 

 particularly in relation to the oscillations of climate, as indicated 

 by recent geological history and the change in levels of the great 

 lakes. These subjects are treated later in this chapter. 



In the Belgian Congo^ a meteorological service under the Institut 

 Royal Colonial Beige was established in 191 1 and reorganized after 

 the war on a somewhat different plan. There are now three first 



^ Information from notes by M. Gasthuys. 



