CORRESPONDENCE 303 



he has not overlooked the possibility of such exceptional precipitation being 

 a result of strong local convergence of air currents. In the case described 

 on p. 105 the duration of the rainfall was about 15 minutes, and it seems 

 not unreasonable to suppose that during this period the upper winds may 

 have caused the air from a considerable region to ascend over the place in 

 question and produce there a total fall far in excess of the amount of water 

 suspended overhead at a particular moment. For an interesting example 

 of this kind of phenomenon I will venture to refer Mr. Redway to my " Report 

 on the thunderstorm which caused disastrous floods at Louth on May 29, 

 1920 " (Air Ministry, Professional Note No. 17, H.M. Stationery Ofifice, 

 London). I would not suggest that cloudbursts in America can necessarily 

 be explained on these lines, but until there is clear evidence to show that the 

 normal causes of rainfall are inadequate, it seems to me unnecessary to call 

 in the agency of waterspouts, unless of course there is some direct evidence 

 that they play a part — such as would be furnished by the invariable appear- 

 ance of waterspouts previous to the occurrence of a cloudburst, in places, 

 moreover, to windward of the subsequent cloudburst. 



The chapter on Precipitation appears to me incomplete in that there 

 is no description of the mode of formation of extensive rain areas of the kind 

 that occur in front of cyclonic depressions in temperate latitudes, notwith- 

 standing the excellent papers on this subject that have been written by 

 V. & J. Bjerknes in recent years (a very good example of Norwegian research 

 in this subject is furnished by J. Bjerknes and H. Solberg's " Meteorological 

 Conditions ioT theFormditionoi'Rain," Geofysiske Piiblikationer, vol. ii, No. 3. 

 An abstract of this work appeared in Science Progress for July 1922. 



E. V. N. 

 July 16, 1922. 



THE BANTU RACES 



From Dr. H. F. Sheldon 



To the Editor of Science Progress 



Dear Sir, — In No. 64 of Science Progress for April 1922 it is stated, 

 on the top line of page 571, by Mr. A. G. Thacker, that the Bantu races 

 reached South Africa after the white man. 



J. A. Mitchell has shown that there is evidence that typhus has existed 

 among the natives of South Africa for many years — they are quite familiar 

 with it under the name of Ifiva Mnyama, or Black-tongued Fever — and about 

 a thousand cases a month are now known. 



Considering the prevalence of typhus before the last century, it would be 

 very unlikely that Whites did not introduce the disease to South Africa. 



The Bantu is inclined to blame the white man for intruding into his 

 peaceful home and for infecting him with typhus. 



The statement of Mr. Thacker would indicate that the Bantu asked for 

 trouble in displacing the Bushman. Are there any parallel records of the 

 position of the Whites and Bantu from the earliest times ? 



In addressing the " Bunga," or native parliament, on the subject of typhus 

 I quoted Mr. Thacker's statement that the Bantu was a later comer to S.A. 

 than the white man, but encountered considerable scepticism. 



The point is, what is the exact meaning of " S.A." as used by Mr. Thacker ? 



Yours, etc., 



H. F. Sheldon. 

 Umtata, South Africa, 

 May z-^rd, 1922. 



