WEATHER BUREAU. 179 



observations. A few facts taken from the records of observations at 

 the " Salton Sea " will serve to show the magnitude of the problem un- 

 der consideration. At tower No. 1, about 1.500 feet inland from 

 the water, pan No. 1, on the ground, gave a total evaporation for the 

 year of about 165 inches, and pan No. 5, 40 feet above the ground, 

 193 inches. At tower No. 2, 500 feet from the shore, pan No. 1 

 swings about 2 feet above the surface of the water, it having been 

 found impossible to float the pans successfully without going to great 

 expense. This pan evaporated about 108 inches during the year, and 

 pan No. 5, 45 feet above the water, evaporated 137 inches. At tower 

 No. 4, 1^ miles from the shore, pan No. 1, swinging about 2 feet 

 above the water, evaporated lOG inches, and pan No. 5, 45 feet above 

 the water, evaporated 140 inches. There was therefore a difference 

 of about 30 inches of evaporation near the water surface of the 

 sea and that taking place 40 feet higher. 



The records from the United States Geological Survey indicate 

 that the " Salton Sea " has been falling at the rate of about 55 inches 

 annually for the past three years. \Vhile it is not known exactly 

 how much water is flowing into the lake through the New and Alamo 

 rivers and from the precipitation on the neighboring country, it may 

 be estimated that it is not over 15 inches, so that the total annual 

 evaporation from the surface of the sea is probably about 70 inches. 



Our experiments have shown that pans of different sizes evaporate 

 at very different rates — a 2-foot pan being represented by the coeffi- 

 cient 6.042, a 4-foot pan by the coefficient 0.036, and a 6-foot pan by the 

 coefficient 0.031. The pans on towers Nos. 2 and 4 were each 4-foot 

 pans. It is not now loiown what the corresponding coefficient of 

 evaporation is for the surface of the sea, but it is probably something 

 like 0.027. If an allowance of 25 per cent is made for the probable 

 coefficient between the 4- foot pan and the large surface of the sea, it 

 would reduce the apparent evaporation to 90 inches. This will be 

 further reduced by computations depending upon the temperature of 

 the water of the sea probably to about 75 inches, which approximates 

 the actual amount observed as above stated. These facts indicate 

 how unsafe it has been to proceed from the observations on a pan 

 placed upon the shore of a body of water to the corresponding water 

 surface, and the necessity of the programme inaugurated by the 

 Weather Bureau has been amplv justified. It is hoped that the final 

 report will be successful in clearing up this last part of the problem 

 regarding the coefficient of evaporation on the large water surface. 

 The formula first used at Reno, Xev., by Professor Bigelow has been 

 verified and proved efficient, working equall}" well in the dry regions 

 of the West and the humid districts of the Eastern States. The wind 

 coefficient is 0.070 instead of 0.0175 as first obtained at Reno. At 

 that time it was not known that the size of the pan was so important 

 in the phenomena of evaporation, and on that account it was not 

 deemed necessary in the preliminary campaign to secure the wind 

 coefficient with such precision. The cooperation with the Reclamation 

 Service and the United States Geological Survey has been very im- 

 portant, and we have now secured corresponding observations at about 

 25 stations in the United States. These data, when published, will 

 give a very good idea of the amount of evaporation. l>ut it is evident 

 that the entire subject is one tliat will always need careful sujjervision. 

 The wind effect is so powerful that in all cases an anemometer must 



