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Show REPORT OF THE CHIEF OF ENGINEERS. 341 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 8l°.5 per day. The average relative humidity was, at sunrise, 0.459, and 3 p. m. 0.173. One experiment, made August 10, after heavy showers over a great extent of the surrounding country, showed a considerable decrease in the amount of evaporation, being 0.18 inch for the 24 hours. The temperature of the air ranged from 71° at sunrise to 99° at 3 p. m., and the relative humidity from O.fi45 to 0.310. The temperature of the river-water was the same as iu the previous experiments. During the latter part of August, the experiments were continued at Camp Mohave. A strong hot wiud blew during the day, commencing about 9 a. m., and lasting with but little interruption until sunset; hence the amount of evaporation was much increased/as will be seen by the following table : Date. Hoars. Remarks. August S3 and 30___ August 30........... August 30 and 31___ August 31........... Temperature of water, 80°, calm. Temperature of water, 82°; strong wind; Hand-storm after noon. Calm. Strong wind. From these few experiments it is impossible to form any correct estimate of th yearly amount of evaporation iu the, vicinity of Camp Mohave, since this amount is subject to so many variations, depending on tbctemperatitreof 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 Septemiier, which have an average temperature of 9A3Ji, than that during the cooler months. The mean temperature of May is 79°.47, while the mean temperature of the remaining months is only 6J:.l F., as shown by the meteorological observations taken at this place. 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 amount of evaporation during the remaining months is equal to that iu the four hot uiouths, 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- Inchey. At Cumana...................................................................130 At Dead Sea.................................................................. % At Marseilles.................................................................73.2 At Palermo................................................................... 58. 4 At Manchester................................................................ 41.0 At London...................................................................28.3 At Kotterdam...............................................................23 At Breslau...................................................;............... 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 l'J to April 2. The water-pan placed on the roof of the conuuauding-oiu'cvr'a quarters was exposed to the direct action of the sun, and the temperature of the water taken when the depth of water iu the pan was measured. Owing to the exposed position of the vessel, and the absence •»t any large body of water in the immediate vicinity, the results obtained are proba-••y in excess of what would have obtained under circumstances similar to those at < amp Mohave. At Indian Wells Station, Cal., observations were made April 12 to 14. Here the ves-*M was placed iu the shade of a tree. In Irftri Dr. Lauderdale, post surgeon at Fort Yuma, made some observations, using wj nuu-gitiige at the post. ,, "August, l^'tf, some experiments were made by Lieutenant Williamson, at Ocoya *;e'£j Tularo Valley, lasting four days. The water-vessel (an ordinary milk-pan) as placed on a staiid 2 feet above ground, and n cover ot' brush built above it. All oi these results are tabulated below : Temperature of air. Mean relative humidity. Evaporation in inches. |
