Minutes of Proceedings. xvii 



driest during the first week of August. October is remarkable for 

 the great number of days upon which the fall has been between 

 J inch and 1 inch ; and there is only one day on record upon which 

 the fall exceeded 1 inch. On the other hand, if it rains in Sep- 

 tember it pours, so that 58 per cent, of the total September fall in 

 26 years has come in seven days. Again, there is only one October 

 known in which the month's rain exceeded 2 inches, and only one 

 known without any rain at all. 



The hourly variation of rainfall gives a curve which is nearly the 

 inverse of the barometric oscillation, and is closely connected with 

 the dew-point curve. Upon the whole, rather more rain falls by 

 night than by day ; but since the number of hours of rain is much 

 greater by night than by day, it follows that the rate of fall is 

 heavier by day. 



The harmonic constants of rainfall, pressure, and vapour-tension 

 are also related to each other. Like the semi-diurnal wave of 

 pressure, the semi-diurnal wave of rainfall frequency varies very 

 little in point of time through the year. The constants for thunder- 

 storms bear a strong family likeness to those of rain. In the paper 

 they are compared with the constants for Basle and Vienna. 



Comparing the rainfall with the Kimberley wind- system, it 

 appears that in any month when the rain is abundant the usual 

 prevailing wind of that month prevails yet more, or, in other words, 

 the rain decreases as the vane shifts from its normal position. 



The temperature of the falling rain is referred to, and the approxi- 

 mate altitude of the clouds at different times in the day and month 

 computed from the known dew-point. It appears that the clouds 

 float at a lower level in the more cloudy months, and that in any 

 month the average altitude of the first plane of condensation wiil be 

 greater as the cloudiness of the sky is less. 



The position of Kimberley in the general scheme of South African 

 rainfall is considered by comparing together the rainfall of 160 

 stations in the country having records of 15 to 20 years or so. 

 Monthly and annual averages are determined for these, both for the 

 separate stations and also for the various areas into which the 

 Meteorological Commission has divided South Africa. Approximate 

 harmonic constants are computed for each area, in terms of the 

 monthly averages, and also for a selected number of the separate 

 stations. The wettest place known in South Africa is probably 

 Maclear's Beacon, on Table Mountain, with an annual average 

 approaching, perhaps, 87 inches. Other wet places are Ceres, 

 Lower Katberg, Hogsback, Evelyn Valley, and parts of Natal, with 

 average falls of 40-60 inches a year. Port Nolloth is one of the 



