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Show 121 experiments. The thermometer ranged during these days from 75° at sunrise to 114° at 3 p. m., 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 August 10, after heavy showers ovt< r a great extent of the surrounding country, showed a considerable decrease iii the amount of evaporation, being 0.18 inch for the 24 hours. The temperature of the air ranged from 71° at sunrise tx> 99° at 3 p. m., aud 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. uiM and lasting with but little interruption until sunset; hence the amount of evaporation was maoh increased, as will be seen by the following table: Date. August 29 and 30 AugurtSO August 9) and 31 August 31 Hoars. 7 p. m. to 7 a. m Temperature of air. Mean relative humidity. 95.1- 74.4 j 0.359 74.4* 92.0 j 0.399 92.0- 72.1 1 0.351 72.1- 92.6 1 0.352 a ce & 0.15 0.69 0.11 0.62 Remark 8. Temperature of water, 80°, calm. Temperature ot water, 82°; strong wind; sand- storm after noon. Calm. Strong wind. From these few experiments it is impossible to form ftDy 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 If we estimate the daily evaporation during June, July, August, and September at one- half of that observed August 29- 31, or equal to 0.392 inch, and that the total amoant 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. AtCumana 130 AtDead& a 96 At Marseilles 73.2 At Palermo 58.4 At Manchester 41.0 At London 28.8 At Rotterdam 23 At Brealao. 14.8 . If we take the mean of the observed daily evaporation at Camp Mohave = .784 mch, 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. AtFort 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 tne pan was measured. Owing to the exposed position of the vessel, and the absence ot any large body of water in the immediate vicinity, the results obtained are probacy in excess of what would have obtained under circumstances similar to those at Lamp Mohave. At Indian Wells 8tation, Cal., observations were made April 12 to 14. Here the vessel was placed in the shade of a tree. In lH6d Dr. Lauderdale, post surgeon at Fort Yuma, made some observations, using j njn- gauge a t the post, r v Ta? a8t' * kr>**' 8 ° l u e experiments were made by Lieutenant Williamson, at Ocoya v^ reek, Tulare Valley, lasting four days. The water- vessel ( an ordinary milk- pan) ^^* placed on a stand 2 feet above ground, and a covor of brush built above it. All ™ these results are tabulated below : |