29 
;ondition wherein the increase in area is in proportion to the 
lepth on the weir. This is the fundamental idea inthe Cip- 
xdetti weir. . . 
This form is equivalent to the rectangular weir, with a 
:riangle added at each end. In order that the flow through 
[he added triangles shall be equal to the amount lost by the 
Contraction, recourse is had to experiments and from calcula¬ 
tion, the inclination of the sides is found to be such that a 
slope of one horizontal to four vertical would be sufficient, 
provided the coefficient of contraction remains constant. 
This is not quite an exact supposition, but the difference is 
insensible. 
The experimentation with water so as to make the re¬ 
sults worthy of confidence requires such exceptional facilities, 
and skill in experimentation, the first of which certainly was 
not accessible to Cippoletti,that he based his confidence in the 
constancy of the coefficient of contraction upon the constancy 
shown in the experiments of Francis and other experi¬ 
menters. The experiments which have been made upon 
this weir seem to have been made in this country. 
Attention was first called to the weir and its adaptability • 
to purposes of irrigation in the first edition of this bulletin in 
1890. Experiments had been previously made on weirs of 
that shape, such as our limited apparatus allowed^ which 
were limited to weirs of 6 and 12 inches in length. Further 
experiments were made under direction of Professor Church 
of Cornell University by T. B. McVickers* but the most com¬ 
plete ones have been made by two students, Messrs. A. D. 
Flinn and Dyer, of the Worcester Polytechnic School of 
Worcester, Mass., who took the subject for their graduation 
thesis. These young men were permitted to use the testing 
apparatus at Flolyoke, Mass., erected under the direction of 
Clemens Herschel, a well known hydraulic engineer. In 
their case the experiments could only be made by compari¬ 
son with the flow over a rectangular weir The measure¬ 
ments were made on weirs 3, 4, 5, 6, 7, 8, and 9 feet long. 
These indicate an error slightly in excess of that expected 
by Cippoletti, and that the coefficient of contraction is less 
than .62 which was taken by him in determining the inclina¬ 
tion of the sides. But the relation between weirs of differ¬ 
ent lengths, that their discharge should be in proportion, to 
their length, is closely true. This is the feature for which 
the weir has been brought forward in the previous editions 
of this bul letin for irrigation purposes.^ 
*Engineering Record , Aug. 13,1892. , 
tManuscript of experiments furnished by Mr. 1 linn. Results to be pub¬ 
lished Trans-American Society Civil Engineers, 1894. 
