This paper was mainly a general account of some extensive experiments on
the flow of water in the Ganges Canal, lasting over four years--1874-79.
Their principal object was to find a good mode of discharge measurements
for large canals, and to test existing formulæ. There are about 50,000
velocity, and 600 surface-slope measurements, besides many special
experiments. The Ganges Canal, from its great size, from the variety of
its branches abounding in long straight reaches, and from the power of
control over the water in it, was eminently suited for such experiments.
An important feature was the great range of conditions, and, therefore,
also of results obtained. Thus the chief work was done at thirteen sites
in brickwork and in earth, some being rectangular and others
trapezoidal, and varying from 193 ft. to 13 ft. in breadth, and from 11
ft. to 7 in. in depth, with surface-slopes from 480 to 24 per million,
velocities from 7.7 ft. to 0.6 ft. per second, and discharges from 7,364
to 114 cubic feet per second. For all systematic velocity measurements,
floats were exclusively used, viz., surface floats, double floats, and
loaded rods. Their advantages and disadvantages had been fully discussed
in the detailed treatise "Roorkee Hydraulic Experiments"--1881. They
measured only "forward velocity," the practically useful part of the
actual velocity. The motion of water, even when tranquil to the eye, was
found to be technically "unsteady;" it was inferred that there is no
definite velocity at any point, and that the velocity varies everywhere
largely, both in direction and in magnitude. The average of, say, fifty
forward velocity measurements at any one point was pretty constant, so
that there must be probably average steady motion. Hence average forward
velocity measurements would be the only ones of much practical use. To
obtain these would be tedious and costly, and special arrangements would
be required to obviate the effects of a change in the state of water,
which often occurred in a long experiment, as when velocities at many