80 Transactions of the South African Philosophical Society. 



in the summer, and as much as 130° in the winter. Therefore the 

 summer extreme may be fully 17° higher than the summer mean, 

 while the winter extreme is not likely to exceed the winter mean by 

 more than 12°. The greatest difference between the mean and 

 extreme readings is found in October, and is nearly 25°. The mean 

 for the year is nearly 138°. 



TABLE I. 



Monthly Mean Values of Solar Eadiation Temperatures. 





Maxima in Sun. 



Maxima 

 in Shade- 



Difference between 



Max. in Sun and 



Shade. 





Mean 

 Observed. 



Extreme 

 Observed. 



Mean 

 Computed. 



C-O. 



C-O. 



Mean. 



Extreme. 



January .... 

 February .... 



May 



July 



September . . 

 October .... 

 November . . 

 December . . 







151-0 

 152-7 

 143-8 

 135-3 

 125-7 

 118-8 

 118-8 

 127-3 

 136-3 

 141-6 

 148-8 

 153-3 

 137-8 







170-5 

 168-5 

 159-0 

 148-7 

 139-6 

 131-1 

 130-2 

 144-1 

 156-1 

 166-3 

 168-8 

 170-5 

 170-5 







152-9 

 149-8 

 142-8 

 133-2 

 123-6 

 118 ; 8 

 121-9 

 128-8 

 138-5 

 146-9 

 151-6 

 153-3 







+ 1-9 

 -2-9 



- 1-0 



- 2-1 



- 21 

 0-0 



+ 3-1 

 + 1-5 

 + 2-3 

 + 5-3 

 + 2-8 

 0-0 



o 



+ 0-3 

 + 0-7 

 - 0-3 

 + 0-1 

 + 0-1 



o-o 



+ 1-5 

 + 1-3 

 + 1-7 

 + 2-1 

 + 1-4 



o-o 







62-4 

 63-0 

 60-2 

 57-8 

 55-0 

 53-9 

 53-1 

 55-5 

 58-1 

 60-0 

 62-4 

 63-0 

 58-7 







77-2 

 74-7 

 75-1 

 69-1 

 68-9 

 66-8 

 67-6 

 73-1 

 79-1 

 75-3 

 73-5 

 74-5 

 79-1 



The differences between the maxima in sun and shade increase 

 with fair uniformity as the temperature rises, that is from winter to 

 summer. From which it follows that the temperature in the sun 

 increases faster than the temperature in the shade. 



It is interesting to compare the observed monthly mean maxima 

 in the sun, one with the other, by means of some fo /mula. Now, in 

 a previous paper it had been shown that the maxima in the shade at 

 Kimberley may be approximately represented by the formula — 



T = AS 2 cosZ + B 

 where on any day 



T is the maximum temperature required; 



S the sun's apparent semi-diameter in seconds of arc (S 2 being 



therefore the relative magnitude of the sun's apparent area) 

 Z the sun's zenith distance ; 

 A and B being constants equal respectively to 73°-4 and 22°*8.* 



* J. R. Sutton, "Some Pressure and Temperature Results," Trans, S.A. Phil. 

 Soc, vol. xi., pt. 4, p. 252, 



