362 Wisconsin Academy of Sciences , Arts , and Letters. 
epilimnion is warming rapidly and but little heat goes to 
deeper water. 
The number given above represents the maximum amount 
attributable to the sun. It assumes that the lake retains all 
the heat delivered by the sun to depths below the surface, 
and that all losses of heat by the lake come from that at or 
close to the surface. This assumption is evidently too fa¬ 
vorable to the share of the sun, especially when we recall 
that three-fourths of the incident heat find no place in the 
heat budget of the lake. The percentage of the sun’s con¬ 
tribution should, therefore, be reduced from the figure 
given above. As an estimate, it might be placed at 10-12% 
rather than 16%; but from the nature of the case this is 
merely an estimate. 
This result can not be carried directly over to other lakes, 
each of which offers its own problem. The sun gives a larger 
percentage of aid in a shallow lake; less in a deep one. It 
does more for a small lake; less for a large one. The trans¬ 
parency or opacity of the lake seems to make little, or no, 
difference in the heat budget; at least within the limits 
found in Wisconsin, where all the water has considerable 
color. The temperature curves and the thickness of the 
epilimnion seem to have no relation to the color of the water, 
such as they plainly have with area and depth. This fact 
alone shows the dominance of the wind as the distributing 
agent for heat, and the very secondary part which the sun 
plays in most lakes. 
For the present the subject may be left with these general 
statements, and with an additional remark on the uses to 
which the work-budget will naturally be put. The work 
budget is derived, not from direct observations, but by in¬ 
ference from the heat budget. It is, therefore, a secondary 
matter and of use chiefly in aiding to interpret the heat 
budget. The total work budget does not add greatly to the 
knowledge obtainable through the heat budget, on which it 
depends. Lakes will naturally be compared on the basis of 
their heat budgets, which come from direct observations of 
temperature, rather than on that of the work budgets de¬ 
rived from the heat budgets. The value of the work budget 
lies chiefly in its application to the deeper strata, first to the 
hypolimnion as a whole, and then to its several strata. 
