An Introduction to the Study of South African Rainfall. 17 



Table 26 enables us much better than Table 25 to subdivide South 

 Africa into suitable rainfall areas. Broadly these are — 



1. Area of winter rains. 



2. Area of summer rains. 



3. Area of spring and autumn rains. 



The characteristic formulae of these give : — 



1 . V T = 280°, more or less ; u x > u 2 or u v 

 Sections I., II., III., belong to this class.) 



2. V, = 60°-100° ; u x > u 2 or u y 



(Sections XV., XIV., XIII., XII., XL, X., IX. E., VIII. E., VII. 



belong to this class.) 



3. V, = 180° or 360° ; u 2 > u 3 or u x . 



(Sections IV. E., IV. W., V. W., VI. W., belong to this class.) 



But there is not really any abrupt transition from one class to the 

 other; and the formula representing any section bears a certain 

 affinity to those representing the areas round about, it. Near the 

 west coast the formulae change the most rapidly. 



Let us first consider the variation of the epoch in Y x as the geo- 

 graphical position charges : — 



Starting from Natal and travelling along the parallel of 30° S., we 



find that the angular magnitude of the epoch becomes smaller, i.e., 



the phase times come later, from east to west. The variations 



are — 



Approximate 

 Area ' Vl * Epoch of Maximum. 



Section XV 101°-5 Jan. 4 



XIII 85 n -8 Jan. 19 



XIV 77°-l Jan. 29 



IX. E 67°-4 Feb. 7 



IX. W 54°-5 Feb. 20 



III 282°-0 July 5 



Travelling west along a parallel somewhat to the north of 32° S., 

 the variations are — 



XII 95°8 Jan. 10 



XI 79°-2 Jan. 26 



VIII. E 67°6 Feb. 7 



VIII. W 44°1 Mar. 3 



III 282°-0 July 5 



2 



