SOUTH AFRICAN MKTI-:()R()L()GV. 279 



AUTUMX AND SpKIN(,. 



The following gives the number of days in each month when 

 Lows or no Lows occur, based on calculations covering the six 

 years 1913 to 1918, inclusive : — 



Low. No Low. Low. No Low. 



January 26 5 August .... 5 26 



February .... 22 6 September . . 10 20 



March 19 12 October .... 12 19 



April 13 17 November . . 18 12 



May 9 22 December . . 21 10 



June 7 23 



July 6 25 



Year (mean) . . 14 16 



Summer (m) .. 19 11 Autumn and 



Winter (m) . . 7 24 Spring (m) 12 18 



It will be seen that Lows are mere prevalent in summer than 

 in winter, and this should be a guide in defining the duration 

 of All High periods. Thus, take July: here the number of days 

 when Lows were present is 6, and as Lows generally last one 

 or two days, there will be 4 periods of Low, which, divided into 

 24, gives the mean number of days in each of the 4 periods 

 w*hen no Lows occur, in this case 6 days ; and s<^ with other 

 months. 



Advent of New Low Pressures. 



It is also important to know where a new Low will appear 

 after a spell of All High pressure. The following has been 

 worked out from six years' observations : — 



