28 



presidential address — section a. 

 Evaporation Records. 



The records at the Union Observatory at Johannesburg show 

 that the average yearly evaporation from a water surface over a 

 period of 15 years (1904-1918) is 67.97 inches, with a maximum 

 of 92.31 inches and a minimum of 51.64 inches respectively. The 

 average monthly evaporation over the period of 14 years is 

 shown below : — 



MoDth. 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



Inches. 

 6.05 



5-34 

 4.94 

 4.80 



438 

 3.85 

 4-34 

 563 

 7-14 

 7-55 

 723 

 6.74 



mmimum 



maximum 



The annual evaporation from a water surface at Johannes- 

 burg and Kimberley is as follows: — 



It will be observed that the evaporation at Kimberley for 

 the 8 years is 88.91 inches, as compared with 63.49 inches for 

 the same years at Johannesburg- 



