52 Report S.A.A. Advancement of Science. 



by a persistent force. And if it should further prove that anti- 

 cyclonic systems occupied a predominant place in the types, their 

 progressive movements might be traceable in the charts. (Here 

 followed 14 lantern slides illustrating the tyfes, and showing that 

 those found to he associated with one another supported the view 

 that the anti-cyclones whicli controlled the distribution of pressure 

 had a progressive movement). 



Let us now consider the lessons which these types teach us 

 regarding the distribution of pressure which we find prevails near 

 South Africa. The principles governing the distribution are the same 

 in each case. They may be summed up as follows : — 



1. The high pressure systems, which are known under the name 

 of the permanent anti-cyclones, have a seasonal migration north and 

 south with the sun. 



2. There is a movement off the land on to the ocean in summer ; 

 and on to the land from the ocean in the winter, but the Atlantic 

 system seldom entirely deserts its position. It is owing to this 

 system, and to those like it which prevail over the oceans, that the 

 migration north and south with the sun has come to be recognised. 



3. At certain times during the winter a continuous belt of high 

 pressure is formed round the globe, which is due to the merging 

 together of all the systems. Each of them, nevertheless, has an 

 individuality which it never loses, and the systems will finally separate 

 and dominate the area to which they belong. 



Whether the formation of an anti-cyclone gives rise to that of a 

 cycloncj or vice versa, and what the connection is between the two 

 are still moot points, but it is certain that the two are concomitant, 

 and that where an anti-cyclone prevails a cyclone cannot rage, nor 

 exhibit its objectionable characteristics. It can, ana does, however, 

 show by various indications, especially in the sky and by changes of 

 pressure, that it is in existence ; and in the writer's opinion it is 

 sometimes superposed above, or partially above, the anti-cyclone. In 

 this way we may account for many of the anomalies which are being 

 disclosed by observations with kites in the upper levels of the 

 atmosphere. 



4. Further, these types support the hypothesis that has been 

 advanced, that the changes which are observed in the distribution of 

 pressure are the result of a regular progressive movement of the 

 permanent anti-cyclonic systems from their extreme winter to their 

 extreme summer positions and back again. Secondary and minor 

 anti-cyclonic systems are formed which have irregular movements of 

 their own, quite irrespective of the general progressive movement of 

 the more permanent systems of which they are off-shoots. 



South African Anticyclones. 



South Africa has two well-defined anti-cvclonic systems near it ; 

 one to the west which, like the system over the Atlantic in the 

 northern hemisphere, prevails very generally over the South Atlantic 

 and seldom deserts it entirely, and the other to the east, which will be 



