88 



Report S.A.A. Advancement of Science. 



The long arrow shows the general movement of the cyclone, the short 

 arrows, the direction of the wind. Such a cyclone brings low 

 pressure, rain and NW gales to the Cape Peninsula, and passes to 

 the south of Africa. If the cyclone is very large, it may extend from 

 Port Nolloth to the Hex River and Port Elizabeth, bringing rain to 

 the whole SW corner of Cape Colony. Passing now to the East 

 Coast rains, we assume that these are due to cyclones in the Indian 

 Ocean whose paths move in latitude with the Sun. In winter time 

 these cyclones are too far north to interest us, but in summer time 

 their path is just to the south of Africa. They come from the NE 

 and turn to the SE as shown on the diagram. 



These cyclones attain two periods of maximum intensity, the first 

 about October or November on the Sun's southward progress, and 

 again in February and March on its northward return. It is to these 

 cyclones that the Transvaal owes its soaking east rains ; unfortunately 

 these rains die away very quickly as the distance from the coast 

 increases, and very few ever reach to our western border. The 

 southern sides of these cyclones bear the heaviest rains. A glance at 

 these two diagrams will show that the extreme south coast is slightly 

 under the influence of both cyclonic systems, and has therefore light 

 rains at all seasons of the year. 



Neither of these systems accounts for our inland rains. These 

 are due to thunderstorms, and are accompanied by the usual barometric 

 anomalies. 



But as already pointed out by Mr. C. M. Stewart, of the Cape 

 Commission, in the last volume of Re-ports of the British Association, 

 South Africa owes most of its characteristic weather to the V shaped 

 depressions which appear between the anticyclones. The diagram 

 shows an ideal V shape. 



