228 



Journal of Agricultural Research 



Vol. X, No. 5 



However, for making the temperature correction on the flowing-water 

 data the temperature figures of corresponding days were used and not 

 averages. An example will illustrate the method; July 13 will be taken. 



Observed mean temperature for tank 15, 75°; evaporation, 0.15 inch. 

 Observed mean temperature for tank 26, 85°; ev^aporation, 0.24 inch. 

 Observed mean temperature for tank 21, 75°; evaporation, 0.12 inch. 

 Observed mean temperature for tank 23, 81°; evaporation, 0.27 inch. 

 Observed mean temperature for tank 24, 85°; evaporation, 0.32 inch. 

 Observed mean temperature for tank 25, 93°; evaporation, 0.43 inch. 



It happens in this case that no interpolation is necessary, since the 

 exact temperature of tanks 1 5 and 26 are found in the other set. When- 

 ever interpolation was necessary it was done by means of a curve. The 

 increase in evaporation caused by the 10° from 75 to 85, tanks 21 and 

 24, is 45 per cent of that from the tank of lower temperature. By assum- 

 ing that this relation holds for the other tanks the observed figures 

 should be reduced by 45 per cent of 0.15 or 0.07 inch, or the corrected 

 evaporation from tank 26 is 0.17 inch. 



During the latter part of August tanks 67 and 68 were installed. The 

 installation is shown in Plate 36, A. The velocities in this experiment 

 also had to be kept low. Table VII gives the final results, the correc- 

 tion for temperature being made in the manner described above. 



Table VII. — Relation between amounts of evaporation from a tank of flowing water and 

 a tank of still water; tanks of equal exposed area, depth of water, and with similar ex- 

 posure. Exposed water surface i foot by 2Sfeet; water about 3 feet deep 



Aug. 28. 



25- 

 Sept. I. 

 Aug. 29. 

 Sept. 7 . 



13- 

 16. 



14- 



Oct. I . 



Aug. 30. 



Sept. 8. 



2. 



25- 

 Oct. 2 . 



Sept. 6. 



7- 



1916. 



Total a . 



Length of 

 run. 



Hours. 



8X 

 12 



s 



12 



8 



10 



8>^ 



Evapora- 

 tion from 



tank 68, 

 still water. 



Inch. 

 O. 17 



• 13 

 .24 

 . 10 

 . II 

 . 22 

 .07 

 . II 

 . II 

 . 10 



•37 

 .28 

 . 14 



• 13 

 •23 



2. 69 



Evaporation 

 from tank 67, 

 flowing water. 

 Corrected for 



increased 

 temperature. 



23 

 07 



14 

 16 

 10 



32 

 32 

 18 

 14 

 26 



2. 92 



Surface 



velocity of 



flowing water. 



Feet per sec. 



.Ratio, ^°^,;°S=^^=i.o86. 

 still 2.69 



