46 Transactions of tJie SoiitJi African Philosophical Society. 



Of course the period is far too short from which to derive certain 

 conclusions. And while some of the observed differences in the 

 quantities were conceivably due to differences of temperature, it is 

 not at all unlikely that a part w^ere due to differences in capillarity^ 

 and a great part also to the wind. For it is clear enough that the 

 surface of No. I. must have been more wind swept than II., and still 

 more than III. 



My own experiments upon the evaporation of w^ater have not 

 lacked variety, albeit not always complete or necessarily convincing. 

 In none of them have I been able to detect the excessive perturbing 

 influence that has been claimed for the temperature of the water. 

 On the contrary, it seems to occupy a comparatively unimportant 

 place in the list of acknowledged agencies. 



Attention may be called here to some rather large numbers given 

 by the Kimberley Waterw^orks Company from a " wrought-iron tank 

 4-feet cube sunk in the ground to within about an inch of the top, 

 and kept nearly full of water." " 



Monthly Mean. 



1891 86*68 inches. January 11*1 inches. 



1892 104-39 ,, February 8-8 ,, 



1893 101-32 ,, March 7'7 ,, 



1894 91-26 ,, April 6-2 ,, 



1895 101-84 ,, May 5-6 „ 



June 4-3 ,, 



Mean.. 97-10 July 4-8 „ 



August 6-4 ,, 



September 8-3 ,, 



October 10-8 ,, 



November 11*0 ,, 



December 12-1 



The greatest evaporation numbers for any Kenilworth (Kimberley) 

 gauge — which, as it happens, are considerably less than those for the 

 Waterworks tank — are derived from the indications of a copper pan 

 8 inches in diameter and about 5 inches deep, kept nearly full of 

 water. The outside of this gauge was protected from the sun's rays 

 by a covering of water, saw^dust, and ^vood. As originally received 

 from the makers it had an inside coating of bath-enamel ; but this 

 got saturated and came off very soon. It always showed signs of 

 liaving once been painted, however, and this may have reduced the 

 capillarity effect. In July, 1897, the covering of the gauge was 

 improved, but this necessitated raising the gauge some 20 inches 

 higher than before. The change seems to have somewhat increased 

 tlie evaporation, while it also seems to have decreased the range of 



* 11. H. Twigg', in the Qiiarterh/ Jounial of the PiOij. ^Ict. Soc, vol. xxii. 

 p. 166. 



