RAINFALL IN TJIE TRANSVAAL. 693 



In very few countries has much attention been devoted to 

 intensity of rainfall during short periods, and the consequent 

 paucity of information precludes comprehensive comparison be- 

 tween the Transvaal and other areas of the world's surface. In 

 the British Isles, however, where data has been assiduously col- 

 lected, only one fall which would lie above the curve for the 

 Eastern Division has been recorded during 46 years.* More 

 especially over the longer periods, where errors of observation 

 are relatively small, the British records fall well below the Trans- 

 vaal. This single comparison at least serves to exhibit more 

 clearlv the great intensities experienced in ]Kirts of this country, 

 where both physical configuration and the character of the rain- 

 fall combine to favour heav\- downpours. Thunderstorms are the 

 principal agents of precipitation, and these storms, usually tra- 

 velling from south-west to north-east, have a motion opposed to 

 the prevailing surface winds. They are thus fed by an absolute 

 movement of the air towards them, not by a relative movement 

 such as would be associated with convectional thunderstorms, 

 travelling in the same direction as the surface ctirrents. 



Incidentally it may be noticed that the December isobars 

 at 4,000 metres, as com]:)uted by Teisserenc de Bort, would neces- 

 sitate a circulation of the atmosphere at the height closely agree- 

 ing with the direction followed by thunderstorms. f Whether the 

 accompanying clouds travel at that height cannot be definitely 

 stated at present, btit it may be remarked that a series of measure- 

 ments made in connection with a storm approaching Pretoria 

 gave 4,465 metres above sea-level as the mean height of their 

 apices. 



With few exceptions, the rainfall data dealt with here are 

 the results of observation with ordinary 5in. gatiges, exposed 

 with their rims 4ft. above ground level. Unfortunately, only a few 

 of the automatic instrttments tised in South Africa ])roduce 

 records adapted to the extraction of short period intensities. 



ON THE DESIRABILITY OF FOUNDING A SOUTH 

 AFRICAN ENTOMOLOGICAL SOCIETY. 



By Antonius Johannes Theodorus Janse, F.E.S. 



(Not printed.) 

 SOME ASPECTS OF MODERN NAVAL DEVELOPMENT. 



Bv Harold Cecil Kenway. 



(Not printed.) 



* British Rainfall, (iqm). 



t Dr. J. R. Sntton states they approach Kimberley from north-west 

 or west (" An Introduction to the study of South African Rainfall." 

 S.A. Phil. Soc, 15. 25). 



