The following is a rule for finding the exact discharge of water in cubic feet, or gallons per second, passing over level weirs. The depth of the water on the weir x width x velocity, all in feet, will give cubic feet, and this x 6 1/4 will give the discharge in gallons. To find the exact quantity of water that is flowing over a weir would be a very difficult matter unless proper provisions were made for gauging the depth of the water and its velocity. I or rough approximation the depth would be the difference in level between the weir and surface of still water above it, but with an allowance for curvature of the surface on the weir, which varies considerably. For the velocity it would be necessary to time the movement of a floating object, and from this make a deduction, as the surface travels at a higher speed than the bottom.