Measurement and Division oe Water. 19 
2. The ratios of the discharge between two outlets should be 
correctly given by the module. 
3. The same module should give the same amount of water wher¬ 
ever placed. 
4. It should be capable of use both in large and in small canals. 
5. It should be capable of adjustment so as to discharge any frac¬ 
tion of its capacity, and thus be used in distributing water pro rata 
6. Any tampering should leave indications easy to recognize. 
7. It should be simple so as to be operated by ordinarily intelli¬ 
gent men. 
8. It ought not to require complicated calculation. 
9. It ought to occupy a small space. 
10. Its discharge ought not to be materially affected by fluctua¬ 
tions in the supplying canal. 
11. Its cost should not be great, nor ought it to require much fall. 
12. It not to be easily put out of order, and if so, the indications 
of its inaccuracy should be easily determined. 
These conditions are evidently not of equal importance. Some 
may be dismissed; the first conditions become increasingdy im¬ 
portant. 
The question of expense mentioned in No. 11 is a relative 
one and may or may not be of importance. As before pointed 
out, it becomes of less importance as the development of the 
irrigated section becomes greater, the need for accuracy more 
felt, and the value of water greater. The conditions that a small 
amount of fall be required is a physical condition which sometimes 
is impossible to meet. Often land lying close to a canal is to be 
served when probably no fall is available. For those places, special 
modules may be required, or special methods. The conditions 
that calculation ought not to be required may become of no par¬ 
ticular weight when suitable tables are provided. 
The condition No. 10 is one which is of more importance 
to ditches where equal division is made among the users. It is 
not of much importance in the larger canals or in those which 
have a ditch rider or patrol who can frequently adjust the gates. 
It sometimes is of importance for canals which have special 
contracts. It is a condition which has generally been considered 
the most important in the early stage of measurement from canals. 
In almost all countries, the first attempt is to give orifices of equal 
size to equal users, and then to make the quantity discharged by 
these equal orifices the same. To do this it has been necessary to 
keep the pressure of water on these orifices the same. Hence the 
module of Milan, the miner’s inch of the various states. This com 
dition is now less important. In our practice it is rarely attempted 
to make the discharges absolutely constant, but rather to perfect 
devices which can be adjusted by the frequent visit of the ditch 
rider. 
The devices for maintaining a constant flow are essentially 
of two classes. First; those which attempt to maintain the pressure 
