MEASUREMENT AND DIVISION OF WATER. 13 
inches in height, with a pressure of water of 5 inches 
above the opening, and that the number of inches shall 
be the same as the number of square inches in the orifice. 
But the term is not confined to the statute inch. On some 
ditches water is measured with a pressure of only two 
inches, on others without any, but the same term is used 
in all. 
An inconvenience which was soon discovered was 
that the discharge through the Milanese module was 
not in proportion to the nominal discharge. A person, for 
instance, drawing 100 inches receives more than ten times 
one who draws 10. This was so noticeable that it was 
not long before the discharge from any one orifice was re¬ 
stricted to a certain number of oncia, generally six. The 
oncia varies from 33 to 47 litres per second, according as 
the orifice discharges one or six, according to Herrison. 
The same thing is true of the statute inch of this State— 
the advantage is entirelv in favor of those who draw the 
large quantities. The reason for this difference comes 
from the different ratio which the perimeters of the open¬ 
ings bear to the areas in the different cases. For example, 
one drawing 24 inches lias an orifice 4x6 inches, the peri¬ 
meter is 20 inches. The orifice discharging 96 inches is 
16x6 inches, with a perimeter 44. The ratio is less than 
J in the last case, nearly 1 in the first, and friction affects 
the smaller opening much more than the larger. 
There are other causes of variation, as in the distance 
the opening is above the bottom of the regulating box, in 
the thickness of the sides, in the manner of its discharge. 
All of which render this module, excellent as its service 
has been in the past, inaccurate and unreliable and is 
leading to its abandonment. 
A module based on an entirely different principle is 
that of the Marseilles canal, one of the most costly in the 
world, considering the amount of water it carries. The 
