juiyao. igi? Evtiporation from Water and River-Bed Materials 223 



quite steady and the results have been incorporated into the final value of the coeffi- 

 cient, 

 where €2=0.023 (1.23)" for 4-hour intervals. 



n =0 for large open water areas, 



n =1 for 6-foot pans, 



n =2 for 4-foot pans, 



n =3 for 2-foot pans, 



n =4 for ordinary dry air. 

 The value of the coefficient for n=i is fairly well determined, and is interpolated for 

 n=4. These should be further verified if possible. 



It will be noted from this extract and by a reference to the original 

 work (3) that the pans used are of the type that is almost entirely ex- 

 posed. The sides of the pans on rafts may have been partly water- 

 covered. The results are not exactly comparable with those obtained 

 at the Denver laboratory; nor would it appear that they could be as 

 safely extended to large water bodies. A comparison on the basis that 

 the results from the 6-foot tanks of each investigation are the same is 

 given in Table III. 



Table III. — Ratio of evaporation at the Denver laboratory and at Salton Sea 



The extension of the results obtained at the Denver laboratory to 

 larger water surfaces is discussed later. 



RELATION be;twe;e;n evaporation from circular tanks and square 



TANKS SET in THE GROUND OF EQUAL EXPOSED WATER SURFACE 



Tank 4 is circular, with a diameter of 3.39 feet and an area of 9.0 

 square feet; tank 3 is 3 feet square; tank 2 is circular, with a diameter 

 of 2 feet and an area of 3.14 square feet; tank 15 is 1.77 feet square. 

 All are 3 feet deep and are set in the ground. Table IV shows the 

 evaporation figures for these tanks. Based upon the totals, the evapora- 

 tion from the larger square tank is 102.7 P^r cent of that from the circular 

 one of the same area; that from the other square one is 103.5 per cent of 

 that from the circular one of the same exposed area. Based upon mean 

 weekly averages, these figures are 104.7 ^^d 104.9. 



