The Venturi Flume 
15 
m) 
reading and also the chance of miscalculating the difference in the 
height of the two water surfaces. After the slides are once set, the 
readings may be read at leisure. 
At each gage well, fixed surfaces or sup- 
ports are required which have the same eleva- 
tion above the floor of the flume. It is thought 
advisable to have these surfaces protected by 
a metal plate to insure permanency. These 
supports should be provided with notches of 
sufficient length and depth to keep the rod 
vertical while observing the heads. - To use 
this adjustable scale, set the slide (A) for the 
water surface in the upper gage well, and the 
slide (B) for the water surface in the throat 
gage well. It is immaterial which slide is first 
set. It is only necessary to move the whole rod 
vertically and at the same time to see that 
it is firmly held in the notch with one hand un- 
til the point (P) exactly coincides with the 
water surface. Securing this position, move 
the slide (A) or (B), as the case may be, 
downward until the stop (a) or (b) rests firmly 
against’ the plate mentioned above. The read- 
ing is similarly observed in the other gage well. 
The upper edge of the pointer on the slide (A) 
will indicate the head (Ha) on the scale (e) 
and the difference in head or (H^) on the 
scale (c). These adjustable scales may be 
made of sufficient length to permit their use 
on moderately deep wells; however, care must 
be exercised in keeping the rod or scale vertical. 
To locate the zero point of the scale (e) 
it is only necessary to measure vertically from 
the point (P) a distance equal to the difference 
in elevation between the floor and the top of 
the supports or notches on the wells. To lo- 
cate, the zero point of the scale (c), place the 
points (a) and (b) at the same elevation and 
adjust the scale to read zero as determined 
by the pointer on slide (A). Where one rod is to be used for a 
number of flumes, it will be necessary to have the fixed surfaces or 
FIGURE 3 — Ad- 
justable Scale for 
Determining the 
Upper Head and 
D i f f e rence in 
Head for Ven- 
turi Flumes. 
