MEASUREMENT AND DIVISION OF WATER. 
19 
weir. Other forms might be as accurate, but no other has 
been subjected to such exhaustive experimental investiga¬ 
tion. Besides, its conditions are easily met, so that one may 
place weirs satisfying these conditions and feel confident 
that the actual discharge will be close to the calculated. 
Because of these facts and the growing importance of 
accuracy, the coming module will be based upon the Aveir. 
It is gradually displacing other types. Australia is using 
it, exclusively, avc think; India, and even in Italy, the origi¬ 
nator of most of our measures, the newer canals are using 
it to the exclusion of the Milanese module. The 
old canals will probably continue the use of the old mod¬ 
ule, for rights have become vested in measurement by 
them, and consumers are jealous of change. A large pro¬ 
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 Canale Villoresi to propose a 
neAV module in obedience to the requirement of the Italian 
Government, says in regard to the weir : 
« 
“ It is indisputably demonstrated that in weirs with 
complete contraction, constructed and observed with the 
necessary accuracy, the coefficient of contraction remains 
constant, and Francis’ formula guarantees the exactness of 
the discharge \\ T ith an error not greater than one-half of 
one per cent, for depths of Avater from 3 to 24 inches; pro¬ 
viding the length of the weir is not less than three—or 
better yet, four—times the depth of water flowing over the 
weir.” (Cippoletti, Canale Villoresi Module per la dis- 
pensa delle acqua, Milano, 1886, p. 35.) 
Cippoletti would, however, use a slightly different co¬ 
efficient. 
The weir is worthy of special attention. Two forms 
will be considered and tables given for their discharge— 
the rectangular weir, whose sides are vertical, which is the 
