20 The Colorado Experiment Station. 
of water constant with the orifices unchanged. Second: Those 
which vary the size of the opening. 
Nearly all modules are of the first class, as the difficulties 
are simpler. 
One was used on the Isabella Canal of Spain, of the second 
class, which seems to have been satisfactory. The old Italian 
modules, the miner’s inch of the western states, is of this class. 
There have been many different kinds of openings, but in all, the 
principle was essentially the same. In the Soldati module of Milan, 
dating from 1585, an attempt was made to maintain the depth of 
water over orifices constant, by the use of a second gate and a 
regulating chamber. The orifice was on the lower end of the 
regulating chamber and the gate between the canal and the 
chamber would be raised or lowered so at to maintain the water 
to constant height. This same device has been used in some boxes 
in Colorado, especially in the one formerly known as the “Max 
Clark box,” but now rarely used. It is an automatic device. If 
the gate is left unregulated, the flow from the orifice will increase 
or diminish in exactly the same ratio as if it came from the main 
canal. Its convenience is in the use of the regulating gate. The 
gate needs to be regulated with variation in the level of the sup¬ 
plying canal. This principle has been worked out with many 
variations in Italy and has led to the adoption of a complicated 
box with many accessories so as to still the waves, to lessen the 
velocity, etc. 
A serious objection to this form is in the supposition that the 
discharge is in proportion to the size of the opening. It was na¬ 
tural to suppose that doubling the size of the opening would double 
the amount of water, and this supposition runs back to the earliest 
Roman times. The attempt to keep the flow uniform reduces the 
inequality but does not cause it to disappear, for while the fluc¬ 
tuation in the head in the second chamber is not as great as in the 
canal itself, yet the fluctuation in quantity in the lateral is as great 
as in the opening coming from the ditch itself, for the opening 
is correspondingly larger. The value of this principle as a regu¬ 
lator is therefore apparent rather than real. Its principal value 
is in the second regulating gate near the canal, and the fact that 
it is possible thus to choke or regulate the quantity received from 
the canal into the regulating chamber. However, unless such a 
box is regulated with every variation in the level of the supply¬ 
ing canal, it does not furnish a constant flow, which has been 
one of its supposed principal merits. 
This box, however, represented a great advance in the prac¬ 
tical measurement of water for irrigation purposes. It was brought 
forth after the great inequality in the division of water was rec- 
