Page:Lowell Hydraulic Experiments, 4th edition.djvu/77

 104. All the apparatus was constructed with great care and precision; the surfaces of the cast-iron guides were ground smooth; and the cast-iron disc and lower crown of the wheel were turned true, and polished, in order to diminish, as much as possible, the resistance of the water to the motion of the wheel.

105. In table V., the quantity of water discharged has been calculated by the formula $$Q = 3.33 (l-0.1 nh) h^{3\over2},$$ in which $$Q=$$ the quantity in cubic feet per second; $$l$$=the length of the weir=3.003 feet; $$n$$=the number of end contractions=2; $$h$$=the depth upon the weir. The weights were obtained for the purpose from Mr. O. A. Richardson, the official sealer of weights and measures for the City of Lowell. The effective length of the lever of the dynamometer, was two feet. The temperature of the water was $63 1⁄2$° Fahrenheit. Temperature of the air at 8h, 35 A. M, 63° Fahrenheit. The weight of a cubic foot of water is taken at 62.3128 pounds, which is deduced from table I.

If, in any experiment, the brake touched, even momentarily, either of the stops $$UU$$, it was rejected; with the use, however, of a regular and sufficient quantity of oil to lubricate the brake, and a properly constructed hydraulic regulator, there is seldom any difficulty from this cause, except at very low velocities. 8