Anticyclones and S.A. Weather. 55 



North- West is by far the most frequent wind that blows next to the 

 South, except in December, when the South-East shares the frequency 

 with the North-West ; (2) that the South wind is most prevalent in 

 the months December-February. 



The hypothesis put forward not only reconciles these different 

 conclusions, but at the same time affords a simple explanation for the 

 recent abnormal drought in South Africa. It also accounts for the 

 position of the core of the anti-cyclonic system so far east in July 

 as the chart of the Meteorological Council, issued in 1900, makes it 

 out to be. 



The theory, as applied to the high pressure systems which 

 influence South African weather may be stated as follows. There is 

 a progressive movement of the South Atlantic anti-cyclone on to the 

 land in winter, and off it on to the water in summer, while the 

 Australian system during the same seasons is moving west and 

 returning east. During winter the two systems merge into one 

 another, and together control the whole of the weather. But neither 

 the tracks they follow, nor the extreme positions they occupy, remain 

 the same year by year. In accordance with some law, of which we 

 have only a glimmering at present, the tracks deviate from an average 

 or mean track, and the extreme winter and summer positions differ 

 from an average or mean position, but they do so without any violent 

 interruptions. The departures from the mean appear to be of a 

 continuous character until a maximum is reached, when there is a 

 gradual return to the mean again, to be followed by a similar 

 departure from the mean in the other direction. We can best liken 

 this to the progressive change in declination, which we see in the 

 moon's orbit year by year round the earth, which reaches a maximum 

 on each side of the equator, but always returns to a mean declination. 

 Owing to this departure of the tracks of the anti-cyclonic systems in 

 coming to and leaving the land, there will be a difference year by year 

 in the seasonal winds experienced by the localities traversed. Some 

 districts which have experienced the calms belonging to the centres 

 of the systems will get the ' winds which belong to the areas north 

 and south of the centre. If the systems are late in going and 

 returning, the winds will show seasonal changes, and if the extreme 

 winter and summer positions are shifted the regions there which are 

 covered by, or which border on, the core, will get an abnormally long 

 season of dry weather. The dry season, which is characteristic of the 

 advent of the anti-cyclone, will be late when the system is late in 

 coming, or early when it is early. Supposing this theory to be correct, 

 the Atlantic system will not pass as near to Cape Town in one series 

 of years as it does in another, and it will be later some years than 

 others. For both these reasons cyclones will be able to approach the 

 Cape with all their characteristic winds and weather ; and the winds 

 which prevailed in the spring and autumn months, as the anti-cyclone 

 was passing, would vary slightly from year to year. When the 

 system was following its extreme track, such variations in the winds 

 would be strongly marked. During the winter months June- August 

 the North-westerly winds belonging to the South-westerly quadrant of 



