32 
DIAGRAM. 
Knowing the depths which may be necessary during the season 
;and the number of days in which it must be applied, the diagram 
shows the number of acres which one cubic foot per second flowing 
constantly during that time will serve, or the duty. Thus if one 
foot is needed for wheat in forty days, look at the right for the depth 
required. At the top find the vertical line corresponding to the 
number of days as forty in which the amount of water is needed, 
say one foot for wheat. At the intersection of the two lines is the 
•diagonal line showing eighty acres as the corresponding duty : 
