I'KKSIDKNTIAI, ADDRESS SECTION A. 



29 



Temperatures. 



At the Union Observatory, Johannesburg, the maximutn and 

 minimum temperatures during each month of an average year 

 are as follows : — 



The above figures were kindly supplied by the Union 

 Astronomer (Mr. R. T. A. Innes). 



The maximum daily temperature recorded was 90° F. on 

 the 23rd December, 1913, and the minimum was 23.1 °F. on the 

 T6th July, 1906. 



The monthly variations over the year are very regular, as 

 will be observed by an examination of Plate No. 5. 



In the Klip River Valley the daily variations are much more 

 pronounced, and 105° F. as a maximum and .S°F. as a minimum 

 have often been recorded at the Zwartkopjes and Ztuirbekom 

 Pumping Stations of the Rand Water Board. 



Influence of Temperature upon Evaporation. 



Some interesting experiments were carried out under my 

 supervision at the Village Pumping Station of the Rand Water 

 Board in January last to ascertain the evaporation of water at 

 different temperatures, and the effect of such increase is shown 

 on Plate 3. 



The test was carried out with water at its natural tempera- 

 ture, which was about 73°F., and also with artificial tempera- 

 tures of about 83° F. and 90°F. The tanks, which were 4 f eet ' 

 square, contained 3 feet 6 in. of water, and were erected at the 

 Village Main Pumping Station, in the centre of Johannesburg. 

 There were thl'ee tanks, one under natural conditions, and the 

 other two were heated artificially by watertight steam coils pass- 

 ing through the water contained in the tanks. As all other 

 frtctors were common to the three tanks the difference in evapora- 

 tion was due to temperature alone. 



