40 BUIXETII^r 854, LT. s. DEPARTIMENT OF AGRICULTUIIE. 
In a like manner, the data for the experimental velocities for the 
selected experiments (Table 4) were substituted in equation 26, and 
the formula for concrete tile became 
7=131 B'-^^ 5«-^o^ (31) 
Noting how close the exponents of R and s were to | and |, it was 
deemed advisable to determine what the coefficient would be when 
using these latter values. For the clay tile, using all the various sizes 
and lengths of tile, the formula became, 
T"=136 7?3s^ ■ - (32) 
In the case of concrete tile, the data for the 4-inch size show that 
greater resistance to flow is offered in this size than in the larger 
sizes. This is clearly shown in the diagram in Plate X as well as in 
column 10 of Table 4. Therefore, it was decided to eliminate the 
4-inch size and use the remainder of the sizes in the derivation of the 
formula. The formula for concrete tile, then, is 
F = 138.2i?«si (33) 
None of the previous formulas were derived from the combined data 
for both clay and concrete tile. Therefore, it was decided to derive 
a formula by using the velocities for both clay and concrete tile flow- 
ing full as obtained from Plate IX. These velocities were plotted as 
abscissae against their respective slopes as ordinates (PI. XII). 
The formula derived graphically for both clay and concrete tile is 
V = 137.9QR'-'' s'-' (34) 
This formula is practically the same as that derived for concrete 
tile as given in equation 33. Since it was derived from the data for 
both clay and concrete tile, equation 34 is recommended as the general 
formula for computing the capacity of tile, merely eliminating the 
decimal in the coefficient and making the exponents f and |, respec- 
tively, thus, 
F = 138i?^si (13) 
FORMULA FOR TILE FLOWING PARTLY FULL 
A great many experiments were made at other depths of flow as 
shown in Tables 3 and 4. These have been plotted and mean curves 
drawn through the points (see PI. IX, figs. 1 to 12). The velocities 
at 0.5, 0.6, 0.7, 0.8, and 0.9 depths and for the tile flowing full were 
read from these curves and plotted on logarithmic charts as abscissge, 
against their respective slopes as ordinates, to determine the equa- 
tions for flow at these different depths. 
Figures 3 to 8, Plate XI, show the studies made of clay tile at 
various depths of flow. With the exception of the 0.5 and 0.6 depths 
of flow (figs. 7 and 8), the lines were dra^\'n through the various points 
by eye, the centers of gravity not being determined anah^tically. 
