178 'Wisconsin Academy of Sciences, Arts, and Letters. 
3% is very far from the exactness expected in a laboratory ex¬ 
periment; but in the present state of our knowledge of lakes, 
a possible variation of 3% or 5%, or even a larger error, does not 
render an observation “futile’’ for purposes of general discus¬ 
sion. 
The same general results as to the relation of observations at 
the center of the lake and those made simultaneously at the 
center and ends can be derived from the observations made by 
Wedderburn and Halbfass (Halbfass 10 a ) on the Madii-See in 
Pomerania. 
In short, so far as I can learn from my own observations and 
from those of others, the statement made in the paper on the 
Finger lakes is correct: “It is fair to conclude that the mean 
temperature of the water of a lake of simple form may be de¬ 
rived from a single series of observations taken at or near the 
center of oscillation of the water.” (Birge and Juday T4, p. 
558.) 
I am confident that this statement is true for American lakes 
in our latitudes up to 10 km.—15 km. of length. My experience 
of larger lakes is limited, but I believe that it holds true for 
them also. How far it is true for European lakes must be 
shown by observations made there. I am prepared to accept 
any conclusion which such studies may warrant, but I shall be 
surprised if observations made at the center of a lake are shown 
to be in general either “futile” or “bedeutungslos” as evidence 
of the mean temperature of the water of the lake. 
I believe, therefore, that the numbers stated in Table A rep¬ 
resent with general truthfulness the heat budgets of their re¬ 
spective lakes. The results obviously include several variable 
features, and they are, therefore, approximate and provisional. 
Yet they come from so many places and so many different years 
that they constitute a “random selection” of the facts. They 
so far agree with each other that certain general conclusions 
may be drawn which further study will doubtless modify, but 
which are not likely to be overthrown. 
