184 Wisconsin Academy of Sciences, Arts, and Letters. 
Warm-See the temperature begins to decline almost from the 
surface. The amount of wind-distributed heat in the lower 
strata of Wiirm-See is as great as in those of Cayuga. But the 
European lake seems to lack the continuous sunshine, heat, and 
light winds of mid-summer which give the American lakes the 
peculiar character of their August temperature curves in the 
upper strata. This difference is apparently the characteristic 
one found when the temperatures of mid-European lakes are 
compared with those of lakes in our latitudes of America, and 
this is the usual cause of the lower heat budget, where such ex¬ 
ists. 
The August temperature conditions in the lakes of central 
Europe, in general, resemble those of American lakes in June. 
In the European lakes a relatively thick epilimnion is not formed 
in early and mid-summer as in ours, and a well-marked 
epilimnion is hardly developed in these lakes until the surface 
begins to cool. Prom this fact comes the statement, not uncom¬ 
mon in European writers on lakes, that the thermocline is a phe¬ 
nomenon which develops during the cooling period of a lake. 
No student of American lakes would make such a statement, 
since the epilimnion is fully formed in July, even in a large 
lake, while in smaller lakes it may be well developed in June or 
even in May. 
In Fig. 1 the number of gram calories in the annual heat bud¬ 
get of each lake is indicated by the length of the line assigned 
to it. The position of the line on the figure indicates the char¬ 
acter of the lake as tropical or temperate, and its position in the 
class to which it belongs. The line marked “0” indicates the 
temperature of 4°. In the case of the temperate lakes the lake 
lines cross the zero line and the length of that part of the line 
to the left of zero indicates the number of calories per square 
centimeter which its water loses below 4° ; or in other words the 
number of calories per square centimeter of its surface required 
to raise its water from the winter temperature to 4°. That part 
Of the line to the right of the zero line indicates the number of 
calories per square centimeter necessary to raise its water from 
4° to the summer'temperature, or the summer heat-income. In 
the case of the tropical lakes the left end of the line is placed 
