METEOROLOGY 121 



in the case of the European cHmate. It seems probable that uni- 

 formly high temperature is a factor adverse to health and occa- 

 sional changes to a cooler climate, either at a hill station or in 

 temperate latitudes, are desirable for Europeans working in the 

 hotter parts of Africa. The adverse effects of high temperature 

 are greatly intensified when it is associated with high relative 

 humidity, as the latter greatly reduces the cooling power of moving 

 air. In desert climates the surprising paradox is found that during 

 the hot dry season there is often actually more moisture in the 

 atmosphere than is normal for Great Britain, but the drying effect 

 of the air is very much greater on account of higher temperature. 

 This has been pointed out by C. E. P. Brooks (1932) and by 

 L. J. Sutton (1923). On the other hand the moisture content of 

 desert air can fall much lower than in temperate climates, and on 

 occasions may be reduced to almost nothing on account of the 

 complete lack of evaporating surface over vast areas. Under these 

 circumstances the desiccating power of desert winds becomes 

 terrible. 



Biologically, light and direct radiation as elements of climate 

 may be fully as important as temperature, moisture, and wind, 

 but this is not always realized, and knowledge of radiation, 

 especially in the tropics, is very scanty. Lately Sir Napier Shaw 

 has drawn attention to this defect in meteorological descriptions. 

 It is significant that medical science has not yet decided what kind 

 of radiation is responsible for the sunstroke from which Europeans 

 so frequently suffer in tropical Africa; some attribute this to ultra- 

 violet radiation, others to infra-red. The first published account 

 of light intensity in the tropics in terms of photochemical units 

 appears to be that of Phillips, Scott, and Moggridge (1931). 

 Working in Tanganyika for a year with an Eder-Hecht photo- 

 meter, they found the light intensity (m.easured in Bunsen-Roscoe 

 units) to be very high, even in the absence of direct sunlight, and 

 this appears to indicate that the unpleasant effects of tropical sun- 

 light on cloudy days result from radiations of short wavelength. 

 In South Africa some preliminary work has been done on the 

 ultra-violet content of sunlight by Osborn and Raftery (1932), and 

 more recently Fraulein Riemerschmid of Jena University has made 

 more detailed investigations of solar radiations in East and South 



