MEASUREMENT AND DIVISION OF WATER. D 
the lower one slightly more. The division is made at the 
upper drop by a movable beak of wood, which may vary 
the width of the opening or entirely close it. The sec¬ 
ond drop is for the purpose of producing a constant cur¬ 
rent away from the point of division. 
MODULES. 
It is not possible to secure a module satisfactory in 
every respect. Some may be available in some localities 
where there is a heavv fall, and not in others where there 
is no fall to spare. 
If a module fulfills the following conditions it may be 
11 ' 
reputed perfect. All the conditions not marked are 
essentially the same as those given by Buffon in his “ Des 
Canaux dTrrigation cle lTtalie Septentrionale,” Yol. I., p. 
445-6 : 
*1. Its discharge should be easily converted into ab¬ 
solute measure, e. g , cubic feet per second. 
2. Modules intended to give equal discharges should 
always discharge the same quantities of water in a given 
time wherever placed. 
/ • 
*3. The ratio indicated by the module to the dis¬ 
charges from two outlets should be the actual ratio. 
o 
4. The flow should remain sensibly unaffected by 
variations in the level of the supplying canal. 
5. It should be as reliable with large as with small 
quantities of water. 
6. Any attempt to alter its discharge should leave 
traces easy to recognize. 
7. It should require but a moderate degree of intelli¬ 
gence to use it. 
8. Calculation ought not to be necessary to regulate 
the discharge of different modules or to determine how 
much they are discharging. 
