1132 
Journal of Agricultural Research 
Vol. V, No. 24 
For similar conditions of weir box, the coefficient c decreases as the 
length of weir crest L increases, and the exponent n increases as the 
length increases. 
As the width of weir box, or end contractions, is increased for any 
certain length of weir, both c and n decrease. This is probably due to a 
decrease in the velocity of approach, owing to the increased area of the 
weir box. 
When the sides of the weir box are parallel, the discharge increases as 
the width of the box is decreased, for all sizes of weirs. 
The greatest discharge is obtained when the sides of the weir box are 
parallel and it decreases as the angle between the sides becomes greater; 
or, stated in another 
way, the discharge in¬ 
creases as the sides 
become more nearly 
parallel, the width of 
the box at the weir 
remaining constant. 
When wings placed 
at the upper end of 
the weir box to form a 
junction between the 
sides of the box and 
the canal bank are 
changed from 90° to 
45 0 with the axis of 
the channel, the. dis¬ 
charge is increased for 
low heads, remains 
about the same for 
heads of 0.7 foot, and 
is decreased for high 
heads. The percentage of change in discharge due to such a change in 
the wings is greater when the sides of the weir box are parallel. 
The ratio of discharge to length of weir decreases as the length of the 
weir increases; or, in other words, the discharge over a 4-foot weir is 
less than four times the discharge over a i-foot weir, as is shown by the 
individual standard equations, Nos. 30 to 34, in Table I. This is the 
inverse of the condition found in rectangular weirs having complete end 
and bottom contractions and negligible velocity of approach. 1 
If the sides of the weir box are continued parallel from a point 20 feet 
upstream from the plane of the weir (fig. 6), instead of being continued 
1 Cone, V. M. Flow through weir notches with thin edges and full contractions. In Jour. Agr. Research, 
y. 5,no. 23, p. 1051-1114. 1916. 
Fig. 8.—Plan of experimental weir box for No. 27, Table I. 
Fig. 9.—Plan of experimental weir box for No. 28, Table I. 
Fig. 10.—Plan of experimental weir box for No. 29, Table I. 
