284 
Transactions of the Royal Society of South Africa. 
of an inC'li. Unfortunately there are no lijgrometric observations taken at 
this gauge. 
It will ]3e seen that, although the conditions attending these gauges are 
dissimilar in several important respects, where the hygrometric conditions 
are observed in the vicinity of the gauges the evaporation will naturally 
bear relationship to the observed relative humidity at each. 
The author has compiled the information for Johannesburg, Newton, 
Kimberley, Bulawayo, for five years ending December 31, 1917. 
He has unfortunately been unable to secure the records of Dr. Sutton, 
Kimberley, for this period, and they are therefore not available for compara- 
tive j^urposes in this paper. The records of Newton, Kimberley, can only be 
looked upon in the light of interesting figures, as owing to there being no 
psychrometric data available, comparison cannot be drawn between relative 
humidity and evaporation, which latter is higher ; and it can be concluded 
that, owi ig to the exposed position of the gauge, the relative humidity will 
be exceedingly low. 
Upon proceeding to plot as a graph the recorded evaporation compared 
with the recorded relative humidity, the author found that when the 
evaporation increased, the relative humidity decreased. 
Bearing in mind the fact that evaporation does not vary as the relative 
humidity, he found that a consistent relation obtained in the graph, between 
the difference of relative humidity and saturation and the recorded evapora- 
tion. That is to say E. varied as 100-H. This factor the author has herein- 
after referred to as the " deficiency factor." Attention is noAv invited to 
the records of Bulawayo and Johannesburg, as shown on the attached 
series of tabulated statements, from which it will be seen that the mean 
annual temperature of each place varies considerably with the annual 
temperature, as follows : 
BULAWAYO. 
JOHANNESBUEa. 
YEAE. 
LAT. 20° 09' 15" S. 
LAT. 26° 11' S. 
MEAN TEMP. 
Max. + Mill. 
Difference 
FEOM Mean of 
5 Yeaks, 
MEAN TEMP. 
Max, + Min, 
2 
Difference 
FROM Mean of 
5 Years, 
1913 
67-P 
+ *54 above 
60-27° 
+ -498 above 
1914 
67-r 
+ -54 „ 
60-74° 
+ -968 „ 
1915 
65-9° 
- 1-20 below 
59-53° 
- -242 below 
1916 
66-5° 
- 0-06 ,, 
60-24° 
+ -468 above 
1917 
66-2 
- 0-36 „ 
58-08 
- 1-692 below 
MEAN OF 
FIVE YEARvS 
66-5() 
4- 1-08 
- 1-62 
59-772 
+ 1-934 
- 1-934 
