220 Transactions of the South African Philosophical Society. 



nearly half as great again as those of the other months, including 

 June. Exactly the same rule holds for Durban. It is during these 

 months of greatest range of pressure on the coast that dust storms 

 are most frequent over the central table-land. 



The mean monthly maximum and minimum temperatures, and 

 their arithmetic mean ; also the greatest and least observed in any 

 month, and the total range, are given below : — 





Mean 



Extreme 



Mean 



Extreme 



M+ m 



Range. 





Maxima. 



Maxima. 



Minima. 



Minima. 



2 









o 



o 







o 



o 



Jan 



75-6 



97 



64-3 



52 



70-0 



45 



Feb. ... 



75-6 



91 



64-7 



54 



70-2 



37 



Mar. ... 



74-6 



101 



62-6 



51 



68-6 



50 



April ... 



73-1 



106 



59-2 



47 



66-1 



59 



May ... 



71-5 



94 



53-7 



42 



62-6 



52 



June ... 



71-4 



91 



50-3 



39 



60-9 



52 



July ... 



69-5 



93 



49-2 



36 



59-3 



57 



Aug. ... 



69-5 



98 



51-7 



37 



60-6 



61 



Sept. ... 



69-1 



98 



54-5 



43 



61-8 



55 



Oct 



70-1 



98 



56-9 



43 



63-5 



55 



Nov. ... 



71-8 



88 



59-9 



48 



65-9 



40 



Dec. ... 



74-6 



94 



62-7 



47 



68-6 



47 



Year ... 



72-2 



106 



57-5 



36 



64-9 



70 



The curve of mean maximum reaches its highest value about 

 the end of January, lagging a month behind the solstice ; but 

 its lowest value is more than two months later than the sun. 

 The curve of mean minimum reaches its highest value during 

 the first week of February, and its lowest during the first half of 

 July. These epochs are probably largely determined by the 

 differences of temperature between land and sea. There is a 

 remarkable difference between the annual ranges of the curves of 

 mean maximum and mean minimum : the mean maximum tempera- 

 ture of the winter months being only 6° or 7° lower than the mean 

 maximum of the summer ; whereas the mean minimum temperature 

 has a range more than twice as great. This is in sharp contrast to 

 the ranges over the central table-land, for at Kimberley, for 

 example, the range of mean maximum is perhaps 30°, and that of 

 mean minimum 24°. The small variation of the mean maximum 

 temperature at East London throughout the year is largely due to 

 the frequent hot winds of the winter months ; while the night tem- 

 peratures during the winter may be reduced more than they are in 

 the summer by the land breeze. The highest shade temperature on 

 record is 106°, the lowest 36°, giving a total range of 70°. 



The high absolute maximum temperatures during the winter 

 months are one of the most noteworthy features in the climate of 



