—28 
value of L to be used in the computation, is .16 less than 10 
feet or 9.84 feet. 
It is seen that the effective length varies with different 
depths with .the same weir. It is because of this, that of two 
weirs, one twice as long as the other, of the rectangular pat¬ 
tern, the one will not give exactly twice as much as the other, 
even for the same depths. But if the two have their effec* 
tive lengths, so that one is twice the other, then the discharge 
of one will be twice that of the other. 
The Cippoletti weir is a form adopted in order that the 
effective lengths are constantly the same as the measured 
length of the weir. 
The weir here called the Cippoletti weir because of its 
originator, is one proposed by Cippoletti to meet the con¬ 
ditions which the Italian government laid upon the company 
which was given a concession of water for the Canale Villo- 
resi, the last of the great Italian canals. This canal was 
built a few years since as a ‘'high line” canal to water land 
above the existing canals. It waters about 125,000 acres, be¬ 
tween the Ticino and Adda rivers, just north of the city of 
Milan. In the act of concession to this canal, the government 
required the company to propose a module for the measure¬ 
ment and sale of water which should be,based upon the 
theory of the weir with free fall, and that the module should 
be accurate. The problem was put in the able hands of 
Cesare Cippoletti, the engineer in charge of construction. 
The problem Cippoletti proposed to himself, was, while pre¬ 
serving the simple and convenient form of the Francis for¬ 
mula, to determine the form and condition of the weir so that 
the discharge should be proportional to the length of the 
weir, and so that no single cause should produce an error of 
more than one half of i per cent. 
Taking the experiments made by Francis as a basis, he 
attempted first to determine a form of the weir in which the 
contractions at the sides should be automatically overcome. 
In the rectangular weir, as already mentioned, the effect 
of the contraction increases in proportion to the depth. The 
idea suggested itself to him, that by making the form of the 
weir so that the area increases by an amount in propor¬ 
tion to the depth on the weir, then if the increase in area can 
be made so as to exactly balance the loss due to the contrac¬ 
tion, the flow through the weir would remain the same as 
though the weir were rectangular, of the same length of sill, 
but without contraction. In other words, the effective 
length would remain the same for all depths. Manifestly, a 
weir of a trapezoidal shape, like that in Figure 7 presents the 
