With this weir, every square inch of water flowing through the opening indicates roughly one cubic foot of water a minute. Thus if the opening is 10 inches wide and the water flowing through it is 5 inches deep, the number of cubic feet a minute the stream is delivering is 10 × 5 = 50 square inches = 50 cubic feet a minute. This is a very small stream; yet, if it could be made to fall through a water wheel 10 feet below a pond or reservoir, it would exert a continuous pressure of 30,000 pounds per minute on the blades of the wheel--nearly one theoretical horsepower. This estimate of one cubic foot to each square inch is a very rough approximation. Engineers have developed many complicated formulas for determining the flow of water through weirs, taking into account fine variations that the farm prospector need not heed. The so-called Francis formula, developed by a long series of actual experiments at Lowell, Mass., in 1852 by Mr. James B. Francis, with weirs 10 feet long and 5 feet 2 inches high, is standard for these calculations and is expressed (for those who desire to use it for special purposes) as follows: Q = 3.33 L H^(3/2) or, Q = 3.33 L H sqrt(H), in which Q means _quantity_ of water in cubic feet per second, L is length of opening, in feet; and H is height of opening in feet. The following table is figured according to the Francis formula, and gives the discharge in cubic feet per minute, for openings one inch wide: TABLE OF WEIRS Inches 0 1/4 1/2 3/4 1 0.403 0.563 0.740 0.966 2 1.141 1.360 1.593 1.838 3 2.094 2.361 2.639 2.927 4 3.225 3.531 3.848 4.173 5 4.506 4.849 5.200 5.558 6 5.925 6.298 6.681 7.071 7 7.465 7.869 8.280 8.697 8 9.121 9.552 9.990 10.427 9 10.884 11.340 11.804 12.272 10 12.747 13.228 13.716 14.208 11 14.707 15.211 15.721 16.236 12 16.757 17.283 17.816 18.352 13 18.895 19.445 19.996 20.558 14 21.116 21.684 22.258 22.835 15 23.418 24.007 24.600 25.195 16 25.800 26.406 27.019 27.634 17 28.256 28.881 29.512 30.145 18 30.785 31.429 32.075 32.733