56 Report S.A.A. Advancement of Science, 



the anti-cyclone will of necessity prevail if the system is over the land 

 and to the eastward of the Cape. As its centre passes west of the 

 Cape that station will get the winds of the South-easterly quadrant, 

 viz., South and South-west; and these winds will tend to prevail as 

 long as the centre of the system is out in mid-Atlantic. 



The theory of the progressive movements of anti-cyclones was the 

 result of examining thousands of synoptic charts, and in this change 

 in the prevalent winds of recent years, which Mr. Stewart has 

 detected, I see a strong confirmation of its truth. 



It is unnecessary to produce any figures to show the great 

 differences of climate which exist between the various parts of South 

 Africa. They are too well known to you. That the Cape has its 

 rainfall in winter, and Natal in summer, is due to the different ways 

 in which these divisions are affected by the two permanent anti- 

 cyclonic systems. The Cape is ruled by the going and coming of the 

 Atlantic system, while Natal owes its dry season to the merging 

 of the Atlantic and Australian systems, and its wet season to their 

 departure. The rainfall of the rest of South Africa is decided by the 

 same controlling forces, according as the path of the Atlantic system 

 lies nearer to, or further from, the districts concerned. The Transvaal 

 and Orange River Colony mostly go with Natal, while the western 

 side of South Africa has practically no rainfall at all in those regions 

 where the Atlantic system dwells longest in its course, but resembles 

 the Cape as we get further to the south, away from the actual track. 

 There are also districts like the comparatively small Knysna Coast 

 District, each with its special rainfall the whole year round, which 

 are said to receive their rain in this way because the winter and 

 summer rains overlap. If we examine one of the most important of 

 these " constant rain " areas we find that the central line through it 

 runs fairly east and west along Lat. 33° 50, with Ladismith and East 

 London at the two extremities. Again, there is no difficulty in 

 tracing this to the lie of the two controlling systems in summer and 

 winter, which allows low pressure to come in between them at this 

 point at one season, and is too far north to keep such systems out at 

 the other. 



It is all-important to trace the extent of the progressive 

 movements month by month of the two permanent anti-cyclones, and, 

 as far as our scanty records will allow, the path along which they 

 travel. The few barometer and rainfall records, supplemented by 

 such observations of the winds as are obtainable, are all that we have 

 at present to guide us. 



Let us consider the Atlantic system first. On the West Coast, 

 Walfish Bay, Lat. 23° S., is the place with the smallest rainfall, 

 amounting to only 0.31 in. a year on the average for 10 years. 

 (Appendix V.) Port Nolloth, in Lat. 29°, has an average of 2.45ins., 

 all of which falls from April to August, and comes " almost wholly 

 from N. or N.W."* 



* Report of Cape Meteorological Commission. 



