—23— 
feet of this may be lessened by making the width of the box 
treater for the greater discharges. 
By making the box longer, so as to increase the length 
of the edge over which the water spills the device may be 
made more sensitive. Mr. J. C. Ulrich, C. E., the successor 
of Mr. Graves as Chief Engineer of several 0 £ thelar <S® (: 
nals in the San Luis valley, and of the North Poudie Cana , 
has in some places adopted on the latter canal a form where 
the box is placed so that it spills on both sides, and the sharp 
edge is rna.de on both sides of the box. 
THE WEIR MODULES. 
But of all forms of modules, or that which best satisfies 
the first condition of accuracy, is the form of opening known 
as the weir, or overfall (French, Deversoir; Italian, Stramazzo, 
German, Ueberfall). It is not intrinsically more accurate than 
many other forms of openings, but as it is so simple that the 
conditions for accuracy maybe readily met, and because there 
is a vast fund of experimental knowledge regarding its be 
havior under different conditions, no other form of opening 
can compare with it in accuracy. . . 
Because of these facts and the growing importance o 
accuracy, the coming module will be based upon the weir, 
“gradually displacing other types. Australia is using it, ex¬ 
clusively, we think; India, to a large extent, and. m Italy, t 
originator of most of our measures, the newer canals are 
usino- it to the exclusion of the Milanese module. 1 he old ca¬ 
nals will probably continue the use of the am! 
rights have become vested in measurement by them and 
consumers are jealous of change. A large portion of the 
newer canals in Colorado provide that measurement shall^be 
made over a weir. So far as learned no canal has abandoned 
its use. Cippoletti, who was commissioned by the Canape 
Villoresi to propose a new module in obedience to tl 
quirement of the Italian government, says in regard to t - 
weir: . 
constructed LuM 
remains constant , and Francis formu a^ guara depths of water from 3 
with an error not greater than one-hat] oj one pei cem. . ptfpr vet 
slab dh«i wt f»gja»«as^ 
Moduio per la dispensa delle acqua, Milano, 18bb, p. Ido. . . 
Two forms will be considered, and tables given for then 
discharge—the rectangular weir, whose sides are vepi ^ 
which is the one ordinarily meant when weir is sspoken of an 
the one which has been the subject of experiment, and V e 
trapezoidal weir proposed by Cippoletti, after a thoroug 1 
