1056 
Journal of Agricultural Research 
Vol. V, No. 23 
In order to refer the elevation of the crest of the notch being experi¬ 
mented with to a reading of the weir-box hook gauge to the nearest 0.001 
foot, the instrument shown in figure 2 was devised. The ends of the 
legs and the hook can be adjusted so as to make the distance from the 
top of the plate to the groove in the legs exactly equal to the distance 
from the top of the plate to the point of the hook. By resting the notched 
legs on the crest of the notch and adjusting the plate to a horizontal 
position with a sen¬ 
sitive level, the point 
of the hook is brought 
to the same elevation 
as the crest of the 
notch. Water is run 
into the weir box, and 
the surface of the 
water is adjusted to 
the point of the crest- 
hook gauge. Since it 
is possible to main¬ 
tain the water level in 
the weir box quite ac¬ 
curately, the hook- 
gauge reading in the 
weir-box gauge box 
is taken to correspond 
to the crest elevation 
of the notch. Re¬ 
peated determina¬ 
tions of this nature 
indicated a high de¬ 
gree of accuracy. 
In order to avoid 
the fluctuating condi¬ 
tions of the flow 
which occur when 
tests are being started or stopped, means had to be provided for quickly 
turning the flow into the channel to the calibrated tanks when the 
desired conditions for the test had been obtained. This is accom¬ 
plished by means of the double shear gate used to close the two 2 2-inch 
circular openings in the spill box. The lever arm of this gate is 8 feet 
long, the disk is seated by means of steel shear springs, and the gate is 
positive and instantaneous in action. When the gate handle reaches 
midpoint of its swing, it strikes a gong, which is a signal to the hook- 
gauge observer to start or stop the stop watch used in recording the 
Fig. 2.—Device used in referring elevations of the notch crest to the 
reading of the hook gauge. 
