52 Transactions of the South African Philosophical Society. 



years. As a matter of fact it happens that a very large proportion 

 of our very windy days are also damper than usual : seven of th& 

 twelve of the days considered of maximum wind-velocity being also- 

 showery ; and the humidity of one being as much as 37 per cent, above 

 the mean of the month ; the average excess very nearly 5 per cent. 



It must not 1)6 forgotten that the above results are derived from 

 the extreme cases. If we consider every day in the year 1900, for 

 the tank only, ^^'Q may arrange the results in the following way : — 



1. First, assigned mean temperatures of the day ; next, how many 

 days there were of these ; lastly, the average evaporation on these 

 days : — 



Temperature. 



No. of Days. 



Average Evaporation. 







Inches. 



Under 50° 



52 



•057 



50-55 



25 



•082 



55-(30 



42 



•098 



60-65 



56 



•108 



65-70 



51 



•156 



70-75 



78 



•202 



75-80 



5() 



•268 



80-85 



5 



•264 



2. The same process for assigned percentages of saturation : — 



Humidity. 



No. of Days. 



Average Evaporation. 







Inches. 



Under 30 % 



8 



•296 



30-40 



75 



•236 



40-50 



79 



•185 



50-60 



88 



•122 



60-70 



54 



•101 



70-80 



42 



•077 



80-100 



19 



•057 



3. The same process for assigned velocity of the wind : — 



Wind. 



No. of Days. 



Average Evaporation. 



Less than 100 m. per d. 



100-150 

 More than 150 



126) 

 IK) 

 123 



Inches. 

 •103 

 •160 

 •191 



