and complaint. Finally the magistrates of Milan attempted 
to regulate matters, and called for plans of modules, and 
gave twelve conditions which a module should satisfy.* 
It was in response to this proposal of the Milan rulers 
that Soldati proposed the module which was adopted and is 
still in use on the canals of that province. 
—-- - - -* ■ - - 
Si 
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CanaV ^ 
• 
Figuee 2. 
The first thing Soldati considered important was to in¬ 
sure that the water should flow with uniform pressure. This 
he attempted to do by the following principle: 
If two chambers are connected, as in the diagram, the 
water in the second chamber will be lower than that in the 
first by an amount depending on the relative size of the ori¬ 
fices. But the depths in the two chambers are in a constant 
ratio. Thus, if the depth in B is 6 inches, and in A i8 inches, 
if the water in A becomes twice as deep, that in B will also 
become twice as deep as before. Under these circumstances, 
an increase in depth of i8 inches in A causes an increase one- 
third as much in B. 
By means of such a regulating chamber, therefore, the 
variations in the height of the water in the canal are lessened 
in the regulating chamber, which is intended to furnish the 
water under constant pressure. While apparently avoiding 
the diffioulty caused by a varying head, this really does not do 
so. As a matter of fact the flow will increase in the same ratio 
for a given increase in depth of the main channel, whether the 
orifice comes direct from the main channel or from the regulating 
chamber, provided it be at the same level. 
The reason for this fact, which is contrary to general 
opinion of those using water from the ditches under such 
systems, is this : As the velocity of water flowing from an 
orifice varies with the square root of the depth, according to 
the familiar Torricellian principle, the discharge for an open¬ 
ing of constant size will vary with the square root of the 
*The history of this event and the trouble is given in Bruschetti’s “ Storia 
del Irrigazione del Milanesi,’" in his complete works. Vol. II., pp. 118-135. It is 
condensed in Buffon’s ‘'Des Canaux d’Irrigation d’ltalie Septentrionale.” The 
twelve conditions are included in the unmarked conditions on page 14. It is also 
given briefly in Smith’s “ Italian Irrigation;” in “ Parrochetti’s Manuals Pratico di 
Idrometria.” 
