15(J «AIX1ALL OF BrLAA\AYO. 



detrimental to agriculture in Matabeleland. Tlie ettect of 

 these droughts Avill appear very distinctly if we g-roup the 

 rains of December and January in periods of ten days. 

 Summing' up in this way the rain that fell from the 2nd of 

 December to the 31st of January from 1897 to 1920, I get 

 the following- totals (the dates are inclusive) : — 



December. 



2—11 ... ... ... 39 inches. 



12—21 30 ,, 



22—31 49 ,, 



January. 



1—10 .... ... ... 31 inches. 



11—20 ... ... ... 4G ,, 



21—30 ... ... ... 45 ,, 



In the second period of December the rainfall is 23 and 

 39 per cent., and in the first period of -lanuary 3(j and 

 33 per cent. loAver than in the periods immediately preceding 

 or following'. These partial minima are due to breaks in 

 the rains that often occurred in December or January. 



In correlating' the exjjansion of the barometric monthly 

 means into a sine series, with these droughts, I have come 

 across the curious fact that the second harmonic seems to 

 bear a very close relation with tlie variation of the rainfall, 

 roughly, between the middle of November and the middle of 

 February. 



In the following table I give the date of the maximum 

 or minimum of the term A.^ sin (T'2 + 2.r) and the rainfall 

 around that date. The table is given for twentv-two seasons, 

 from July, 1897, to July, 1920. The season 1901-02 is 

 omitted, as there was a break in the liarometric observations. 

 In seventeen seasons the maximum falls in a period of drought 

 or of serious shortage in the rains, and the minimiim in a 

 period of excessive rains. In four seasons there is a period 

 of drought immediately preceding or following the maximum. 

 In one season, 1918-19, the maxinuim falls in the middle of 

 a period of good rains, preceded and followed bv a notable 

 shortage of the rains. In each c^ase I have given to the 

 nearest half-inch the average rainfall for twenty-three years 

 during the period under consideration. 



