The range of variation of both up- and downstream water-levels through which the discharge remains constant is more than sufficient to meet all the requirements of irrigation canals. The sufficiency of the delivery can be ascertained at a glance. The water can be drawn from any desired depth in the parent channel. When desired, means are provided whereby the supply can be closed or opened at will. Means are provided, if desired, for a sudden increase of discharge when the upstream water-level exceeds a certain limit, so that surplus water, which might endanger the safety of the canal, is allowed to escape into the branch whenever the danger limit is reached. The upstream water-level at which escapement begins can be fixed in accordance with the requirements of each site, and the action of the escape notch is independent of the opening and closing of the module. No designing or calculations are required. These have already been worked out. Known the discharge required, the module is supplied complete and ready for setting in position in the canal bank. HYDRAULIC PRINCIPLE. The entire absence of moving parts is the chief feature of Gibb’s module; the water simply regulates itself by using up all the excess of energy over and above that required to discharge the correct supply of water. The way in which this takes place will be understood from the following analogy:-- We all know that when we stir tea in a cup so as to make it spin, the liquid rises at the rim of the cup and curves down into a depression in the middle, and the greater the spin the more marked this effect is. It is, we know, the centrifugal force produced by the spin that makes the tea remain high at the rim of the cup. If, while the tea is thus spinning, a teaspoon is held so that it dips slightly below the surface of the liquid near the rim, it will obstruct the flow of the outer portion of the liquid, which will fall in towards the depression in the middle. The reason for this, of course, is that the centrifugal force is absorbed when we interrupt any part of the spin with the teaspoon; hence the liquid must fall, and we know that when liquid falls it uses up “head” or energy.