238 . A. G. Howard.— The [May 4, 



■side, while the upper current being intensified would rush over the dense 

 bank of high pressure, and down through the temperate zone to the 

 pole, displacing the polar current, but by that very act giving strength 

 !to this polar high pressure area and causing a return oscillation. 



Now let us note the effect of the inclination of the earth's axis, 

 whereby the sun appears to travel during six months over a belt of 

 47 degrees of latitude, that is, from 231° n. to 23J° S. Owing to 

 "this apparent motion of the sun, as the disturbed portion is always, 

 in the first instance, where the sun is vertical, the belts of high and 

 low pressure are constantly oscillating north and south, one complete 

 oscillation taking twelve months to perform. Thus, Cape Colony, 

 when the sun is at its southern limit, has the south tropical belt of 

 high pressure to the south of it ; but when the sun is at its northern 

 limit, this belt is far to the north of us, and we are on the northern 

 €dge of the temperate-zone area of low pressure. Were it not for 

 the unequal distribution of land and sea, the arrangement of atmos- 

 pheric pressure would be regular, and as sketched above, but as it 

 is, it is far from being so, although on the whole, it is as I have 

 described it, which is near enough for the purpose of investigations 

 where Cape Colony alone is concerned. 



By taking the mean barometer readings for different months, and 

 extending over a number of years, isobaric charts have been compiled, 

 and these shew very clearly the distribution of high and low pressure. 

 By referring to one of these for January, it will be seen that a large 

 bank of high pressure lies to the south-west of us, and another to 

 the south-east, being joined together by a col or neck of compara- 

 tively lower pressure. The centre line of this area is the limit of the 

 ordinary influence of the equatorial indraw, but when great distur- 

 bances take place, the indraw extends further south, and the upper 

 -current becomes intensified, bringing violent south-easters over the 

 Colony, and storms in the area of low pressure to the south of us, 

 which after a definite period, return from the south on to the Colony, 

 with north-west winds and rain. 



To the north of the Colony, and stretching well to the interior of 

 Africa, is a wild Karoo, hot 'and dry, called the Kalahari Desert, 

 with extensions to the West Coast and down to Namaqualand. This 

 hot plain plays an important part in our Colonial meteorology. The 

 constant heat generates a const nt upward flow of air, and a 

 consequent surrounding circulation. Thus over the Orange Free 

 State and at Kimberley the wind flowing round this area is north or 



