Anticyclones and S.A. Weather. 53 



referred to as the Australian system. Not having as yet any Marconi- 

 grams to report their movements at sea, we must turn for assistance to 

 such charts of pressure as we possess, and to those of currents and 

 hurricanes. In Buchan's excellent set of synoptic charts of 

 atmospheric pressure, the mean positions of these systems appear for 

 each month of the year. The charts were compiled from the best 

 records which were available for the 15 years 1870-84. The 

 movements of anti-cyclonic systems which have been traced in daily 

 synoptic charts of the northern hemisphere, help us to fill in the 

 movements of the southern systems from one month to another, as 

 follows : — The Australian system reaches its extreme easterly position 

 off the west coast of that continent about February. From about 

 November to February low pressure has prevailed, for the most part, 

 both over Australia and South Africa. From March to May the 

 Australian system travels westwards over the Indian Ocean, 

 approximately within the parallels of 30° S. to 40° S., always 

 migrating north, as a whole, wi:h the sun. During the same months 

 the South Atlantic system, which had previously been in a central 

 position in mid-Atlantic, has moved eastwards and has extended across 

 South Africa, trying to merge with the Australian system either in 

 April or May. A complete belt of high pressure, similar to what 

 exists during mid-winter in the northern hemisphere, is being firmly 

 established across South Africa. In July the commencement of the 

 return of the two systems to their summer positions begins to be traced 

 on the charts. It is noticeable that just as we saw in the types high 

 pressure systems identifying themselves in winter with certain regions 

 of America and Europasia, so we find in the southern hemisphere 

 certain similar high-pressure systems identifying themselves with 

 regions of South Africa and Australia. 



In addition to Buchan's charts, we have a series published by the 

 authority of the Meteorological Council of Great Britain, which 

 brings our knowledge of the movements of these anti-cyclojiic systems 

 to the year 1900. When the two are compared we find that in their 

 main features the progressive movements are the same in both, but 

 there is one difference which is of great importance in its bearing upon 

 the second point in our hypothesis regarding the departure of the 

 anti-cyclones from a mean path. In the chart for Julv the maximum 

 pressure is found in recent years to be lying much further east than 

 previously, and to be to the south-east of Mauritius. The Atlantic 

 system is merged with it right across South Africa, without anv centre 

 of pressure or core in mid-Atlantic, as was the case in July up to the 

 year 1894, at any rate. This supports the view which has been 

 advanced, viz., that these systems not only depart from a mean track 

 in going from and returning to their extreme winter and summer 

 positions, but that they sometimes are early, and sometimes late, in 

 leaving them. 



I mentioned in explaining the types that in the northern 

 hemisphere winds blow round an anti-cyclone centre in the same way 

 as the hands move round the face of a clock, while in the southern 

 they blow the reverse wav, or anti-clockwise. Charts of ocean 



