INVESTIGATION OF FLOW OF WATER IN UNIFORM CHANNELS. 361 
and the sides were 13 cm. deep. At intervals of 75 cm. along 
the channel notches were cut in the edges of the planks, to carry 
cross bars which were fixed at right angles to the axis of the 
channel, and having two opposite faces perpendicular to this axis. 
On the down-stream face of each cross-bar was fixed a paper 
millimetre scale, a horizontal line on which was taken as the zero 
line for measuring the distances to the surface of the water. These 
measurements were made by means of a boxwood scale 20 cm. in 
length, having a hole drilled in one end and a needle glued therein. 
A guide block (illustrated in Fig. 2) was constructed to enable 
this scale to be slid up and down perpendicularly to the axis 
of the channel in any position across the channel. Since the 
surface of the water was, in the nature of things, covered with a 
multitude of small ripples, it was assumed that the surface of the 
water had been reached when the needle point was immersed as 
often as not in the course of a few seconds. It was found possible 
generally to observe the ordinate to the water surface to ‘01 cm. 
As will be shown subsequently, the error involved in measuring 
the cross sectional areas is a small one. The stations at which the 
cross-bars were fixed are lettered A, B,...H, but observations were 
rarely taken at either A or H, as doubtless the conditions at these 
points would be considerably affected by the proximity of the 
channel entrance and exit. During the course of the experiments 
readings were frequently taken down to the sides of the channel 
in order to detect any change that might have occurred in the 
Cross-section of the channel due to warping or any other cause. 
In addition to the support at its upper end, the channel was 
carried in notched standards attached to trestles and capable of 
being adjusted to any desired height, so that its slope could be 
easily and rapidly changed. As the lower end of the channel 
warped slightly in an approximately vertical plane during the 
course of the experiments, a weight of 28 Ibs. was hung on the end 
of the channel in the later experiments, and the supports adjusted 
So as to make the slope as nearly uniform as possible, this latter — 
being estimated by means of an ordinary hand level. The channel 
t 
