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The National Geographic Magazine 



River, the precipitation and the evapora- 

 tion are about equal to each other — 40 

 inches per year ; on the Rocky Mountain 

 plateau the precipitation is about 20 

 inches and the evaporation 60 inches, and 

 in the southwestern states the precipita- 

 tion is only 10 inches and the evaporation 

 80 inches. The available water is there- 

 fore derived from the melting snows of 

 the mountains, brought under control by 

 the rivers and the canals to the fertile 

 soils of the arid regions, and this means 

 the construction of storage basins, which 

 are subjected to intense evaporation. 



Mr Gilbert's suggestion resulted in a 

 conference board from the U. S. Geolog- 

 ical Survey, the U. S. Reclamation 

 Service, and the U. S. Weather Bureau 

 visiting the Salton Sea and reporting that 

 the project of studying the laws of evap- 

 oration at the sea should be undertaken, 

 and that the work should be under the 

 immediate control of the U. S. Weather 

 Bureau. 



There have been several important and 

 careful researches made regarding the 

 probable law of evaporation from small 

 pans, with the view of connecting the 

 amount of water delivered by a pan to 

 that given off by a lake or large body of 

 water in the same climatic conditions. 

 It is much to be desired that the law shall 

 so be expressed that from the given me- 

 teorological data of a locality the corre- 

 sponding amount of the loss of water in 

 a basin of any size can be computed. 

 Unfortunately the results of these re- 

 searches are by no means in agreement. 



In view of the fact that an expensive 

 campaign is being planned at the Salton 

 Sea, to extend over several years, it 

 seemed prudent to attempt to gain some 

 better ideas regarding the physical prob- 

 lems involved before beginning the work 

 in the desert. 



THE STATION AT RENO, NEVADA 



After consideration it was decided to 

 set up at Reno, Nevada, a temporary ex- 

 periment station, planned to bring out 

 the causes of the disagreements. In 

 summer the dryness of the climate at 



Reno is about the same as at the Salton 

 Sea, and the amount of evaporation from 

 a small pan is nearly the same in amount, 

 nearly 8 feet per year ; but the discomfort 

 of working in the open is not nearly so 

 great, on account of its elevation, 4,500 

 feet above sea-level. Our experience 

 showed us that Reno possesses an un- 

 usually agreeable summer climate, with 

 cool nights, not very hot days, and plenty 

 of wind from the mountains to keep up a 

 very pleasant circulation of the air, espe- 

 cially in the afternoons. 



We set up five towers, 40 feet high, by 

 August 1, 1907, and continued regular 

 observations till September 15, by which 

 time we had secured all the records 

 needed for our preliminary studies, some 

 35,000 observations, including 100,000 

 readings of our instruments. There were 

 29 evaporating pans placed in position, 

 five 6-foot pans in the water or on the 

 ground near the base of the towers, and 

 twenty-four 2-foot pans on the stagings 

 above the surface. The records were 

 taken every 3 hours during the day, from 

 5 a. m. to 8 p. m., and readings were made 

 at 1 o'clock, just after midnight. These 

 included the temperatures of the water 

 surface, of the air at half an inch above 

 the water, and of the air at two feet above 

 the water of each pan. The vapor ten- 

 sions, dew-points, and the amount of 

 water evaporated were also on the 

 program. The wind velocity at different 

 heights, from the bottom to the top of the 

 towers, was observed, and some new 

 Pische evaporimeters were employed, 

 with the purpose of ultimately substi- 

 tuting them for the large evaporation 

 pans. 



The serious trouble with all this class 

 of meteorological work is that there is no 

 suitable self-registering apparatus for re- 

 cording the wet-bulb thermometers or of 

 getting the vapor contents of the air con- 

 tinuously. The consequence is that we 

 must read the instruments many times 

 daily, in order to obtain any correct 

 knowledge of the variations of all these 

 elements with the heating and cooling of 

 the atmosphere in the course of the day, 



