Birge—Heat Budgets of American and European Lakes. 205 
tional range in its budgets due to a considerable variation both 
in the winter and in the summer temperatures. I cannot assign 
any reason for this wide variation, nor can I state why its bud¬ 
gets should rise so much higher than those recorded for the 
other lakes. 
If the temperatures of Thuner See are derived from Halb¬ 
fass’ table of 1910, they will be found somewhat lower than • those 
given, which are from his paper of 1905. The annual heat bud¬ 
gets, however, are but little altered by the change. 
The summer temperatures for Ziiricher See were all taken in 
July and may be lower than the maximum. 
Nos. 18-20.—These lakes continue in Austria, at a consider¬ 
able distance, the series of Swiss lakes which ends with Con¬ 
stance and they lie substantially in the same latitude. Their 
heat budgets are also approximately the same. 
It will be remembered that there is a doubt both as to the 
area and depth of Hallstiitter See. I have taken the smaller 
figures. If the larger are taken, the [budgets will be increased 
by about 15%. 
No. 19. MilSatter See.—Halbfass (13a, p. 312) compares the 
temperatures of Gmundener (Traun-) See and Millstatter See as 
taken on Aug. 20, 1913. Tie finds the latter lake “erheblich 
warmer” than Traun-^ee, and thinks that the difference may 
perhaps be due to the east-west direction of the long axis of 
Millstatter See, while that of Traun-See lies north and south. 
The case is, however, not so simple as this suggestion would 
imply, and Halbfass has not called attention to the peculiarity 
which seems to be the most important one. The upper strata of 
Millstatter See are indeed warmer than those of Traun-See, as 
are those of Atter-See (see below). But from a depth of 15 m. 
down Traun-See is the warmer and this is the more significant 
difference between the temperatures of these lakes. 
The observations on Aug. 20, 1913, did not extend to such 
depths that the mean temperatures of the lakes can be computed; 
but there can be no doubt that on this occasion, as on all others 
in late summer, Traun-See contained much more heat than 
Millstatter See. The latter lake agrees in general with the 
other lakes of its class in the Alps, both as to the amount and 
the distribution of its heat. Traun-See is the exceptional case 
among these lakes. The interesting question is not so much 
