Birge—Heat Budgets of American and European Lakes. 181 
Traun-See, where the large budget of 1895 is in striking con¬ 
trast with the ten others , and must be regarded as exceptional. 
On the other hand, certain lakes with several budgets seem quite 
as regular as the American. Such are loch Ness, lago di Bol- 
sena, Zurieher See, Boden-See, and probably Wiirm-See. This 
regularity, where it exists, is the more noteworthy since the years 
from which budgets are reported cover a much wider range than 
is the case with American lakes. i 
The range of European budgets is so large that there is no use 
in calculating their mean. That of the American lakes is 36,000 
cal., and the mean departure of each observation is less than 
1,800 cal., or 5%. The maximum departure is +5,900 and 
—3,100, or a range of 25%. So far as the evidence goes, there¬ 
fore, the heat budget of American lakes of the first class lying in 
the region of lat. 43° is in general much higher and more uni¬ 
form than that of European lakes of similar character. 
The amount of the summer heat-income in the temperate 
lakes is shown in the following table: 
TABLE 4 
SUMMER HEAT-INCOME OF EUROPEAN AND AMERICAN LAKES 
Calories 
European 
American 
Budgets 
Lakes 
Budgets 
Lakes 
Below 20,000 . 
16 
7 
0 
0 
20,000-25,000 ..... 
27 
10 
4 
3 
25,000-30,000 .... 
11 
5 
18 
6 
30,000-35,000 ... 
5 
3 
1 
1 
35,000-40,000 .. 
4 
2 
0 
0 
Above 40,000 .... 
1 
1 
0 
0 
64 
16 
23 
7 
In this table the same facts are evident as in Table 3. More 
than 20% of the European budgets lie below any American; over 
40% more lie in the class which contains less than 20% of the 
