MEASUREMENT AND DIVISION OF WATER. 15- 
the plug are properly proportioned—and it is easy to cal¬ 
culate them —this module ought to be a very satisfactory 
one. It has the disadvantage of requiring a considerable 
fall, but it avoids the friction which must interfere with 
the action of the Marseilles module. For a discharge of 
1.44 cubic feet per second, generally estimated enough for 
80 acres, with a hole 12 inches in diameter, the following 
would be the diameters for the given depths from the top 
of the plug: 
Diameter 
in feet. 
3 inches_0.53 
6 “ 0.70 
12 “ _0.80 
2 feet _0.87 
4 “ 0.91 
9 “ 0.94 
THE SPILL-BOX OR EXCESS WEIR. 
Another means of procuring a constant head is one due 
to A. D. Foote, of Idaho, recently in charge of the Snake 
River Division of the Irrigation Survey, a cut of which is 
given in the Engineering News of November, 1886, and 
more fully described in the transactions of the American 
Society of Civil Engineers, Vol. XVI. 
In fig. 3, A is the main ditch, with a gate forcing a 
portion of the water through box B. This has a board on 
the side towards the main ditch, with its upper edge at 
such a height as to give the required pressure at the ori¬ 
fice. Then if water be forced through B, the amount in 
excess of this pressure will spill back into the ditch. If 
the box B is made long enough and the spill-board be 
sharp edged, nearly all the excess will spill back into the 
ditch, thus leaving a constant head at the orifice. Mr.. 
Foote gives this the name of excess weir. He constructed 
one for trial purposes. To Mr. W. H. Graves, of Monte 
Vista, is due its introduction into use on the large canals* 
