Diurnal Meteorological Conditions at Kimberley. 135 



If, for example, we wished to compare the average shade temperature 

 of clear and of cloudy days in any month, we could not justly draw 

 conclusions from a mere average of tabulated results, should it happen 

 that the beginning of the month was clear and the end cloudy ; for 

 the simple reason that our previous discussions have established the 

 intimate relation existing between the maximum temperatures of the 

 air and the varying altitudes of the sun day by day. In Table 1 will 

 be found the average zenith-distance of the sun on the clear days, 

 compared with the average of all days, month by month. The values 

 are reduced from the sun's declination published by the Nautical 

 Almanac (p. II). And since there is a good deal of difference at 

 present between these declinations on a given date in different years, 

 all four years have been used rather than trust to a mere approxima- 

 tion derived from one year only. The result is so far satisfactory, 

 that the greatest departure from the mean zenith-distance of the 

 month is just over one degree of arc, in April, corresponding to a 

 time-interval for the season of about three days. The Table also 

 contains the number of clear days found for each month, showing a 

 variation in the number of clear days from 25 per cent, of the whole, 

 in summer, to 60 per cent, in winter. 



Table 2 gives the cloudiness of the sky, month by month, from 

 ■observations taken at intervals during the day. It will be seen that 

 the mean cloudiness of the months, given in the last column but 

 one, does not always agree with the average of respective hours. 

 The deviation arises out of the circumstance already noted that only 

 three observations ^jcr diem were taken in 1898 and 1899. The 

 bottom line gives clear indication of at least a double diurnal oscilla- 

 tion, one maximum being in the vicinity of XIV., with a minimum on 

 either side at about XI., and perhaps later than XXIII., respectively. 

 We shall see later on that an analysis of the more important meteoro- 

 logical elements indicates a very curious determination of the diurnal 

 cloud-period. The last column contains the average monthly per- 

 centage of cloud on the days we denote clear. The results, of 

 course, neglect some of the night hours. Hourly observations of 

 cloud all over the world, and particularly in South Africa, are badly 

 wanted for the purpose of determining the diurnal period. 



It is scarcely necessary, perhaps, to introduce the element of sun- 

 shine here, although at some future time I hope to bring it under the 

 notice of the Society. Some results of observations taken with a 

 Jordan Eecorder, however, for the eight years 1894-1901 will be 

 found in the Meteor ologische Zeitschrift for May, 1902. 



Table 3 shows the mean temperature of the air, hour by hour, in 

 each month and for the year. Since no individual monthly series of 



