Page:Lowell Hydraulic Experiments, 4th edition.djvu/84

 obtain the fall acting upon the wheel. The velocity of the wheel was obtained by means of the counter $$W$$. The apparatus for lubricating the brake is not represented on the plate; in some of the experiments, water was used, and in others, linseed oil.

The experiments were made according to the method of continuous observations, which has been sufficiently described in the account of the experiments on the Tremont Turbine.

115. The experiments on the Boott centre-vent water-wheel, are given in detail in table VI, which will be intelligible, without much further explanation than is contained in the respective headings of the several columns.

116. 10. Useful effect, or the friction of the brake, in pounds avoirdupois raised one foot per second. The brake was connected with the vertical arm of the bell crank, by a link, which was horizontal when the brake was in its normal position. When in this position, the length of a perpendicular, from the centre of the vertical shaft, to the line joining the points of the brake and bell crank to which the link was attached, was 9.743 feet; the effective length of the vertical arm of the bell crank, was 4.5 feet, and of the horizontal arm to which the scale was attached, 5 feet; consequently, the effective length of the brake was $${{9.743 \times 5} \over 4.5} = 10.826\ \text{feet.}$$ 117. 15. Quantity of water passing the wheel, in cubic feet per second, This quantity was gauged at the weir. The length of the weir was 13.998 feet; the width of the raceway on the upstream side of the weir, was 17 feet; the crest of the weir was 11.14 feet above the bottom of the raceway. The quantity has been computed by the formula $$Q = 3.33(l-O.1nh)h^{3\over2},$$ determined from the experiments made, in 1852, at the Lower Locks. (See art. 258.) In this formula