Birge—Heat Budgets of American and European Lakes. 211 
No. 133. Ladoga.—The summer temperature given for this 
lake is very probably too high. It comes from a series taken on 
October 17. The mean temperature derived from a series on 
Sept. 7 of the same year was 0.85° lower, indicating a gain of 
nearly 4800 cal. per sq. cm. between these two dates. Such a 
gain at this time of the year is quite impossible, since it must 
be as much as half the total radiation from sun and sky. Either 
the earlier series is too low or the later one is too high and no 
important conclusions should be based on this single budget. 
It may very likely be true, as stated by Halbfass (’10, p. 63), 
that ‘‘die Warmezunahme des Ladogasees iibertrifft die des 
Wurmsees ganz ausserordentlich ’ ’; but the maximum budget for 
Wurm-See is 25,600 cal., while if the September temperature is 
taken for Ladoga, its budget would be 28,500. This difference 
or that shown in the table hardly warrants so strong an asser¬ 
tion. Very probably, however, the mean of a series of years 
would show that the budget of Ladoga is the greater, since its 
temperature is very low both in winter and summer. A large 
part of its gain of heat, therefore, lies below 4° and just above 
that point, and at these temperatures, a larger percentage of in¬ 
cident heat will be stored than at higher temperatures, like those 
of Wiirm-See in summer. 
In concluding these notes on Table A, I will add that I have 
given care to secure accuracy in the numerical data which it 
presents. I can not even hope that complete accuracy has been 
attained; when I follow the work of others in this field I find 
what seem to me to be errors and I can not doubt that similar 
mistakes occur in my data. But I believe that such errors as 
may be found to exist in the table—as in the other cases to which 
I referred—are not numerous or serious enough to invalidate or 
weaken the general results announced in the paper. 
I ought to conclude this paper, as I began it, with acknowl¬ 
edgment of indebtedness to the work of Professor Halbfass. 
(’05, ’10) from which so much of my data has been derived. 
