Transactions of the Royal Society of South Africa. 
Althougli the factors on the annexed tables give the mean daily evapora- 
tion in inches, and although the author concludes as per the preceding 
paragraph that the evaporation is dependent upon the hours of sunlight, the 
fact must not be lost sight of that a certain amount of evaporation takes 
place during the night, owing to terrestrial radiation. 
Dr. Sutton has shown that at Kenilworth approximately one-third of the 
total daily evaporation takes place during the hours of the night. 
One point must not be lost sight of, and that is that these results have 
been based on observations taken at 8.30 a.m. daily, and that the recorded 
evaporation is that of the whole twenty-four hours of each day. It is quite 
reasonable to suppose that the relative humidity varies during each hour of 
the day, so that in the event of records being taken by subsequent observers 
the E. per deficiency factor may be found to be lower than in these conclu- 
sions. The results can therefore only be regarded as relative. 
The author has annexed a table based upon Dr. Sutton's figures showing 
the mean annual evaporation for each hour of the twenty-four at Kimfcerley, 
and as an additional proof that evaporation follows closely upon the ' deficiency 
factor ' of humidity the lines of this factor per hour are shown. 
In presenting this paper to the Society the author has refrained from 
evolving a formula, being content to show the recorded evaporation at gauges 
that he has seen and considers to be the best available ones existing. 
He trusts that he has made it clear. 
It is to be hoped that meteorologists and engineers will follow up by further 
research on the lines above indicated, with the view to the establishment of 
a formula which will not be only suitable to Africa, but to the whole world. 
EVAPORATION • THE OBSERVATORY • BULAWAYO- 
LAT 20°09-1.6 LONG. a8°36-3.E AUT.4460rT 
SUMMARY OF OBSERVATIONS FOR PERIOD OF FIVE YEARS. 
YEAR 
EVAPOR/3J10M 
TOTAL INCHES 
PERAHrtUM. 
WIND 
ME/vtH 
M lUES PER 
Diem. 
MEAN AmMUAL 
TEMPERATURE 
M E/^h Annual 
relative: 
HurvilDlTY. 
MEAN AHMUAL 
DEFIOELMCV 
OF 
RELATIVE 
HUM 1 DITY 
lOO - H . 
MEAN ANNUAL 
BVA PORATIOM 
IN IPicHES 
PCT 1% DEFlClErtCY 
OF RtUATlVe. 
HUMIDITV. 
MEAN DAIL-S" 
E.VAPORAT\OM 
IN INCHES PtR 
l%DEffCIEriCY 
OF REUATWC 
MUM 1 OVTY 
1913. 
83-30. 
171-6. 
671. 
59 
41 
2031707 
0055663. 
1914. 
76-47 
192-0. 
67-1 
6^. 
36. 
2124167 
•0058197 
1315. 
6832 
176-4. 
65-9. 
69. 
:3i. 
2- 139355 
•0058612. 
1916. 
7662. 
179-1. 
665. 
63. 
37 
ZO7OS08. 
■0056579. 
1917. 
71-94. 
180-5 
66-2. 
65. 
35. 
2-055429. 
0056313 
MEAN OF 
36. 
2-081389. 
nVC YEARS 
74-93. 
179-92. 
66-56. 
64. 
-0057024. 
Table 1. 
