372 Wisconsin Academy of Sciences , Arts , and Letters. 
Plate I. Diagram for determining RT for the several one-meter 
strata of lake Mendota (after Schmidt ’15, fig. L). The volume of 
the lake below any level whose volume has been computed, is 
platted on the proper line and the points thus determined are 
joined by a curve. In this case the points are at 0, 3, 5, 10, 15 and 
20 m. Horizontal lines are then drawn for each meter of depth. 
From the intersection of these lines with the curve perpendiculars 
are drawn to the scale at the bottom. Then the distances on the 
scale, 0-1, etc. are proportional to the reduced thickness of the several 
one-meter strata. Their numerical value may be ascertained by meas¬ 
uring these distances, and computing their value as percentages of 
In this case the entire length 
of the scale corresponds to a mean depth of 12.1 m. Since, how¬ 
ever, the volumes of the several strata are likely to be needed for 
other purposes, it is quite as easy to determine these from the 
diagram and ascertain RT directly by using the formula 
