Birge—Heat Budgets of American and European Lakes. 207 
See and Traun-See show that in every case where temperatures 
were)observed on closely adjacent days, Atter-See had a higher 
temperature at the surface and in the upper strata; but at a 
depth of 50 schuh (15.8 m.) or more, Traun-See was the warmer. 
It is plain that the larger amount of heat in Traun-See depends 
not Jon the reception of a greater supply at the surface, but on 
the greater efficiency of the means of distributing it to the deeper 
water, or on the larger supply brought to the middle and lower 
strata of the lake by the river Traun. The temperature records 
for both lakes come from Milliner ’99. 
No. 25. Tegern-See.—The budget of this lake is very probably 
affected by its altitude which is greater that that of any other 
lake in the table. The temperatures for this lake come from 
Breu ’06. 
No. 26. Arend-See.—This small lake is placed in the table to 
show how close the heat budget of a small European lake comes 
to that of the larger lakes. An American lake of the same size 
would show a smaller heat budget. This lake is not used in the 
general discussion of results. 
Nos. 27, 28. Loch Ness, Loch Morar.—I have included bud¬ 
gets from four of the Scotch lakes. All of them have been com¬ 
puted by myself from data derived from Murray and Wedder- 
burn. I have taken as the winter temperature of loch Ness 
Wedderburn’s estimate of 41.2° F., 5.10° C. The temperature 
given in the table for Sept. 15, 1904 is the mean of five series 
taken near the center of the lake on such dates in mid-September 
as to make the mean date fall about Sept. 15. 
The winter temperature for loch Morar in 1887 is taken from 
the bottom temperature found on April 29th of that year. The 
lowest temperature recorded is 41.8° F. Halbfass’ figures (’05 
p. 227) for Sept. 9, 1887 are undoubtedly]too high. 
It is difficult to understand why the budgets of loch J Morar 
should be so much smaller than those of loch Ness. The maxi¬ 
mum depth of loch Morar is greater, and both its mean depth 
and area are ample to insure a maximum heat budget. No such 
difference appears in the budgets of the mid-European or the 
American lakes. It is possible, that, since loch Morar is situated 
nearer the sea, the greater cloudiness prevents the temperature 
of the water from falling as low in winter as does that of loch 
Ness. If, however, the budgets were to be as great as those of 
loch Ness, the summer temperatures must also be decidedly 
