Page:Lowell Hydraulic Experiments, 4th edition.djvu/56



75. For the purpose of presenting a general view of the experiments, the coefficients of effect, at different velocities, are plotted at figure 1, plate VI., on a system of coördinates. The ratios of the velocities of the interior circumference of the wheel, to the velocities due the fall acting upon the wheel, given in column 20, table II., are taken to represent the velocities; these ratios are here called the velocities, and are taken on the axis of abscissas AX; the corresponding coefficients of effect given in column 17, table II., are taken upon the axis of ordinates AY.

76. The line C D represents the experiments made with the regulating gate fully raised; — to avoid confusion a portion of the experiments are omitted; — the experiments represented are those numbered from 4 to 42, inclusive, which were made in regular sequence, with gradually increasing weights. It will be observed in the table of experiments, that several trials were made with the brake entirely removed; these were made, generally, after the wheel had been left for some time, for the purpose of seeing if it was in as good running order as usual; if any material change had taken place, it would have been indicated by a change in the velocity of the wheel.

The experiments thus made, omitting experiment 12, in which the height in the wheelpit was not observed, are collected together in the following table.

The greatest variation in these velocities is in experiment 13, which is $1⁄738$ part below the mean; the running condition of the wheel must, consequently, have been nearly uniform.

In all the experiments with the brake removed, the coefficient of effect, of course, is nothing, and they would be represented on the diagram by points on the axis of abscissas; for the sake of distinctness, only one of those tried when the gate was at its full height, is represented on the diagram.