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Show 121 experiments. The thermometer ranged during these days from 75° at sunrise to 114° at 3 p. ra., while the temperature of the river- water varied from 79° to 81°. 5 per day. The average relative hnmidity was, at sunrise, 0.459, and 3 p. m. 0.173. One experiment, made Angust 10, after heavy showers owr a great extent of the snrrounding country, showed a considerable decrease iu the ainouut of evaporation, being 0.18 inch for the 24 hours. The temperature of the air ranged from 71° at sunrixe to 99° at 3 p. m., and the relative humidity from 0.645 to 0.310. The temperature of the river- water was the same as in the previous experiments. During the latter part of August, the experiments were continued at Camp Mohave. A strong hot wind blew during the day, commencing about 9 a. m., and lasting with bat little interruption until sunset; heuce the amount of evaporation was much increased, as will be seen by the following table : Date. August 29 and 3 0 . . .. Angust30 August 30 and 31 August 31 Hours. 7 p. m. to7a. m o 1 perat air. a0> H 95.1- 74.4 74. 4* 92. 0 92. 0- 72. 1 72.1- 92.6 > 2= 3 a P 3g * 0.359 0.399 0.351 0.352 a § rf 2- g « a* . 2 0.15 0.69 0.11 0.62 Remark 8. Temperature of water, 80°, calm. Temperature of water, 82°; strong wind; sand- storm after noon. Calm. Strong wind. From these few experiments it is impossible to form any correct estimate of th yearly amount of evaporation in the vicinity of Camp Mohave, since this amount is subject to so many variations, depending on the temperature of the air and water, relative humidity, and force of the wind. It is evident, however, that the monthly evaporation will be much greater during the four hot months, June, July, August, and September, which have an average temperature of 94°. 8, than that during the cooler months. The mean temperature of May is 79°. 47, while the mean temperature of the remaining months is only 65°. 1 F., as shown by the meteorological observations taken at this place. If we estimate the daily evaporation during Jane, July, August, and September at one- half of that observed August 29- 31, or equal to 0.392 inch, and that the total amount of evaporation during the remaining months is equal to that in the four hot months, we get a total yearly evaporation of- 95.77 inches, which compares well with the observed evaporations in other localities. Thus the yearly evaporation is- Inches. At Cumana 130 At Dead Sea* 96 At Marseilles 73.2 At Palermo 58.4 At Manchester 41.0 At London 28.8 At Rotterdam 23 At Breslan 14.8 If we take the mean of the observed daily evaporation at Camp Mohave = .784 inch, we find that the daily evaporation from 556 square miles of lake- surface will equal the discharge of water in the river for 24 hours at the same place. At Fort Yuma experiments were made from March 19 to April 2. The water- pan placed on the roof of the commanding- officer's quarters was exposed to the direct action of the sun, and the temperature of the water taken when the depth of water in the pan was measured. Owing to the exposed position of the vessel, and the absence of any large body of water in the immediate vicinity, the results obtained are probably in excess of what would have obtained under circumstances similar to those at Camp Mohave. At Indian Wells Station, Cal., observations were made April 12 to 14. Here the vessel was placed in the shade of a tree. In 1868 Dr. Lauderdale, post surgeon at Fort Yuma, made some observations, using the rain- gauge at the post. In August, 1853, some experiments were made by Lieutenant Williamson, at Ocoya Creek, Tulare Valley, lasting four days. The water- vessel ( an ordinary milk- pan) was placed on a stand 2 feet above ground, and a cover of brush built above it. All of these results are tabulated below : |
