2IO Jour7ial of Agricultural Research voi.x, no.s 



on quite an extensive evaporation investigation. Available funds lim- 

 ited the work of 191 6 to this evaporation study, divided into two impor- 

 tant parts — that from water surfaces and that from the surfaces of river- 

 bed materials. 



PART I.— EVAPORATION FROM WATER SURFACES 



An early study of evaporation was that of Perrault, who worked with 

 water and soils in 1670 (20). Dalton in 1802 (6) first put his investiga- 

 tions into definite form, and Dalton's law has been used by more recent 

 experimenters as a basis for the expressions which they have proposed 

 for calculating evaporation rates. A bibliography of some length pre- 

 pared in 1908 (19) would tend to show that evaporation research is not 

 in a pioneer state. Noteworthy among the investigations are these: 

 Thirteen years' work at Lee Bridge, London, England (12); 11 years' rec- 

 ords at Boston, Mass. (9); records at Rochester, N. Y., from 1891 to 

 the present (21); records at Fort Collins, Colo. , from 1 887 to the present 

 (5,25); several investigations of the Army engineers (15); measure- 

 ments made at Salton Sea (2); at Owens Valley (18); Coyote (7); and 

 Kingsburg, Cal. (4); and miscellaneous studies by the United States 

 Weather Bureau, the United States Reclamation Service, the United 

 States Geological Survey, and the Division of Irrigation Investigations 

 of this Oifice. However, a recent paper (8) describing the problem of 

 arriving at the amount of evaporation from a reservoir brought out such 

 discussion as to indicate that there is much uncertainty concerning the 

 interpretation of the available data. Regarding the rates of evaporation 

 from water surfaces of varying sizes, one investigator (3, p. 11 34) says 

 regarding the coefficients proposed : 



These should be fxirther verified if possible. 



Other important points were not definitely determined, and funda- 

 mental engineering data upon which to base irrigation research were not 

 available. Accordingly arrangements were made to make studies along 

 the following lines : 



(a) Variation in the amount of evaporation from pans of varying sizes. 



(6) Variation in the amount of evaporation from pans of varying 

 depths. 



(c) A comparison of the amount of evaporation from flowing and still 

 water. 



(d) A comparison of the results obtained from different types of so- 

 called standard evaporation pans. 



(e) A comparison of the evaporation amounts from round pans and 

 square pans of small size. 



(/) An extension of the results of experimental pans to larger water 

 surfaces. 



