Birge—Heat Budgets of American and European Lakes. 189 
A large part of the difference between the budgets is due to 
the higher winter temperature of Wurm-See, 3.30° as compared 
with 2.23° in Cayuga. This difference on a mean depth of 54 m. 
would make the annual heat budget of Cayuga about 5,800 cal. 
larger (more than one-half the difference in the budgets) than 
that of Wurm-See. In the wind-distributed heat therefore, 
the two lakes differ much less than in the annual heat budget. 
The summer heat-income of Cayuga lake is about 5,600 cal. 
larger than that of Wiirm-See. Over 80% of this difference lies 
