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Show 120 Wetted perimeter = p = 1116.7 feet. r = 4.144 feet. b = .713 foot. For the same reasons as at Stone's Ferry, but few subsurface- floats were observed, and the mean velocity has been computed from the nieaji surface velocity, as at that place, but here a correction was made, for wind. The results obtained are as follows: Force of wind = / = - f- 1.5. • V = r 2508.64 feet, and Q r o = 11610.93 + 12.5 = 11623.43 cubic feet per second ; 12.5 cubic feet added represents the discbarge through the chaunel uot included in the section. The river fell 5.11 feet from July 9 to September 5, according to observations taken at Camp Mohave. During the interval between August 11, when current observations were taken at Stone's Ferry, aud September 3, when taken at Camp Mohave, the river at the latter place fell 1.84* feet. This will account for the greater portion of the difference between the discbarge at Stone's Ferry aud that, at Camp Mohave, as a rise of 1.84 feet will cause a corresponding increase of section at the latter place of over 2,000 square feet. A small portion is lost by evaporation, but a considerable quantity flows below the bed of the river, iu sections where the bottom is sandy, as at Camp Mohave. CUKRBNT OBSERVATIONS AT FORT YUMA, CAL. Here the conditions were more favorable. Two boats were obtained, one of which • was used to pick up the Hiibsnrface- floats after passing through the sections. The sections were also more regular than at the former places, aud mid- depth floats could be sent out from all boat- positions without the anuoyance of having them drag on the bottom at any point. The floats were of the same character as those already described, except that no trail- line was used with the subsurface- floats. The observations were taken March 15 to March 20, 1876. The river was then at its lowest stage, and at a constant height ( or nearly so) during the time of observation. The base- line was 300 feet long, measured along the right bank below the ferry. The following values were obtained : A = 2726.5 square feet, W= 461.0 feet, p = 466.2 feet, S Fall per mile as determined by leveling = 1.21 feet. r = 5.848 feet, b = 0.62* 1 foot, With the above values, aud the formula for mid- depth velocities ( formula ( 25) H and A), we have: V = 2.809 feet, and 2 = Va= 7658.74 cubic feet per second. The following table gives the number of floats from which the calculations were made, and the mean surface on mid- depth velocity in each division at the three places where observations were made: Mean division velocities. Divisions. Stone's Ferry Camp Mohave - Fort Yuma No. of 1 floats. J 98 173 80 M .94 .39 1.73 H III. 1 I 1.68 3.12 . 90 1. 65 2.77 2.60 > > 1 3.113.94 2. 73 3. 19 2.69 2.78 M > 4.41 3.13 2.78 VII. | 4.04 3.06 2.74 VIII. 3.35 2.92 2.90 a 2.26 2.76 J. 22 X 1.08 2.41 2.89 M X 1.67 Remarks. Surface- floats calm. Surface- floats wind- up= l- 5- Mid- depth floats. Divisions. Camp Mohave Fort Yuma No. of floats. 98 173 80 XII. L51 XIII. 1.64 XIV. 1.92 > X 2.21 > X 2.77 H* M > ' > X X 3.06,2. 86 XIX. 2.00 ... X 1.35 XXI. .94 XXII. .50 Remarks. Surface- floats calm. Surface- floats wind up-' Mid- depth floats. The accompanying sketches aud profiles show the location of the bases and the topography in the immediate viciuity, as well as the form and area of the sections. EVAPORATION. Experiments on the amount of evaporation were made at Stone's Ferry and Canop Mohave. The vessel containing the water was placed in the river so that it wouM retain the temperature of the river- water. The results were as follows: . At Stone's Ferry several experiments, each one lasting from 2 to 3 days, showed tn evaporation to be 0.23 inch per 24 hours. The atmosphere was dry and either calmo stirred by gentle breezes; a few sand- storms of short duration occurred duringtD |