A Contribution to the Study of the Rainfall Map of South Africa. 375 
cLose neiglibourliood of the sea,* and which come at any season, though 
perhaps the most j^ronounced of them have been in the winter. The sea-gale 
rainfalls are almost invariably associated with a high barometer, while 
the thunderstorms are as characteristically low-barometer phenomena. 
Since the winds of Maritzburg, where Mann's observations were takeu, are 
cliiefly east to south-east, this observer concluded that Natal must be within 
the zone of the south-east trade winds, and get its rain from them. 
Further up the coast, however, in the district of Lourenco Marques, the 
rainfall becomes less — a fact which does not support Mann's idea. Moreover 
the same easterly and south-easterly winds blow also in the winter when the 
interior of Natal is dry. 
A typical instance of heavy winter rain occurred on the Natal coast May 
31-June 1, 1905, when the following rainfalls were registered in 24 
hours — 
Inches. 
Umzinto 17-45 
Verulam 1213 
Durban . . . . . 1070 
Maritzburg 4'00 
Estcourt ...... 2-05 
Utrecht 1-01 
showing a progressive decline of intensity as the storm worked inland. It 
is indeed these sea rains which make up the high mean winter rainfall of the 
whole eastern coast belt, saving that of Lourenco Marques, from Port Alfred 
to the tropics. 
The following list shows how the annual rainfall varies going from west 
to east across the Continent, between latitudes 29° and 30° S. : 
Inches. 
Port NoUoth . . . HI . . . 2-28 
Kraaifontein . . . ,, . . 5*01 
Pella „ ... 3-09 
Kenhardt . . . . IX . . . 5-50 
Prieska .... ,, ... 974 
Grriquatown . . . ,, . . .13-66 
Kimberley .... ,, ... 17-57 
Bloemfontein . . . XI Y . . .21-94 
Thaba 'Nchu ... „ ... 25-13 
Lady brand .... ,, ... o0-60 
Maritzburg . . . . XV . . . 35-38 
Durban .... „ ... 40-54 
This gives an annual average increase of rainfall of about one inch for 
each 22 miles further east. Between Port Nolloth and Kimberley there is 
* E,. J. Mann, "Contributions to the Bleteorolo-^y of Natal," 'Quart. Journ Met. 
^oc.,' October, 1878. 
