Diurnal Meteorological Conditions at Kimberley. 145 



3. From first maxirQum to second minimum : — 



Clear skies -086 -088 



Cloudy skies -093 



4. From second minimum to second maximum : — 



Clear skies -049 -048 



Cloudy skies '061 



The column headed "• Eeduced " above, means that the diurnal 

 curve of pressure has been reduced to re-enter. Evidently a clear 

 sky reduces, and a cloudy sky increases, the range of pressure in 

 every case excepting the second. Eemembering that a clear day 

 increases the range of temperature, this fact seems to confirm the 

 origin of the primary maximum in the temperature, and the inde- 

 pendence upon the same of the other phases. 



The mean morning minimum only falls '003 inch below the mean 

 pressure, and the evening maximum only rises '009 inch above it. 

 It is difficult to state the corresponding amounts when the sky is 

 clear or cloudy because of the secular increase and decrease already 

 referred to. If we eliminate the appearance of this secular change 

 by the addition and subtraction, as necessary, of a number varying 

 with the time, we find that the morning minimum under both clear 

 and cloudy skies, falls, as in the mean case, '003 inch below the 

 average of the day ; the second maximum, however, is '004 inch 

 above the average when the sky is clear, and -012 inch above when 

 it is cloudy. 



Table 21 is worth a little attention. It gives the average pressure 

 for each of the twelve-hour periods beginning at the time in the first 

 column. The mean annual Kimberley pressure over the night hours 

 averages 26*1382 inches, and over the day hours 26*1398 inches — 

 pretty much the same thing ; or, to be more precise, one pole of the 

 great circle bounding the two hemispheres over which the average 

 pressure is the same, is slightly in advance of the subsolar point. 

 It is therefore unquestionable that the view held by some meteorolo- 

 gists ''' that there is a bodily transfer of air from the light hemisphere 

 to the dark, cannot be sustained by the evidence of the barometer 

 alone. 



If we suppose Kimberley conditions to be general — incorrectly, of 

 course, but for the sake of simplifying the argument — the hemi- 

 sphere whose pole is not far from VI. will have the maximum 

 pressure, and that at XVIII. the minimum. Also the meridian 



* E.g., Sir John Herschel, Meteorology, 2nd ed., pp. 72, 73, and 161. 



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