6 BrLLETIX S-Si, U. S. DEPAETMEXT OF AGPJCULTUEE. 
WEIRS. 
For use in measui-ing the water entering into and discharging from 
the tile line, brass, triangular-notch weks were used, the notch angle 
being 90 degrees (PL II, ^g. 1, and PL III, figs. 1 and 3). For tile 
over 4 inches in diameter, weirs with i-inch lips were u^ed; while 
for the 4-inch tile, knife-edged weu's were deemed the most accurate. 
The weir plates, both of which were set level, were so placed that the 
nappe of each weir cut free and was fully aerated. 
To determine the discharge over the weirs, V. M. Cone's formula, 
was used in aU computations. In this formula, Q = discharge in 
cubic feet per second and 5" = head in feet on weir notch. 
HOOK GAGES. 
Boyden hook gages were used to determine the head on the weirs. 
On both gages the vernier plates were secm^ely fastened and bradded 
to the gage, so as to eliminate any error due to possible charge of 
position of the plates. Each gage was set at a distance of over 2 Hto 
the side of the weir so as to record the correct head on the weir. 
FLUME. 
In order to test the carrying capacity of the tile bedded in earth 
as in .actual practice, a continuous wooden flume (PL TV) 570 feet 
long, 2 feet wide, and 2 feet deep was constructed of 2-inch plank. 
All joints and seams were calked with oakom and covered with pine 
pitch to make the flume water-tight. This continuous channel or 
flume was supported on yoke blocks suspended by f-inch steel rods 
{Aj PL Y) from 6 by 6 inch caps {B, PL Y) which rested on 4 by 4 
inch vertical posts (C, PL Y).' Two vertical posts ^nth their yoke 
block formed a bent; the bents were spaced 8 feet apart. In aU, 
72 bents were erected. Each bent was braced by 4 by 4 inch posts 
{D, PL Y). 
METHOD OF CHANGING GRADE. 
The upper 6 feet of the steel rods were threaded ^vith 10 threads 
to the inch. For support on the caps, bearing plates with ogee 
washers and 2-inch hexagonal nuts were used. To raise the flume 
an inch at any bent it was necessary to turn the nuts just 10 revo- 
lutions. Ordinary wrenches were cumbersome and slow for turning 
these nuts, consequently specially-constructed socket wi-enches 
(PL YI, flg. 1) were used, consisting of hollow pipes so shaped as to 
fit over the nuts and with circular disk handles. This type of wrench 
greatly facilitated the work of changing grade. 
1 Journal of Agricultural Research, U. S. Department of Agriculture, Vol. V, No. 23, p. 1083. 
