CLASSIFICATION OF LAKES ACCORDING TO 
TEMPERATURE. 
GEORGE C. WHIPPLE, 
DIRECTOR oF MT. Prospect LABORATORY, BROOKLYN WATER DEPT. 
In view of the increasing attention that is being given to the 
study of the temperature of the water in lakes and ponds it 
seems advisable to establish some system of classification by 
which we may group these bodies of water according to their 
temperature, thus giving additional value to the data accumu- 
lating on the subject. A suggestion for such a classification is 
here presented. It may add to a better understanding of the 
subject if we refer briefly to the temperature changes which 
take place in a body of water and the practical importance of 
the physical phenomena which they produce. We cannot do 
better, perhaps, than to take Lake Cochituate as an example 
and study it by the aid of the diagram in Fig. 1. The curves 
in this diagram are based on a seven years’ series of weekly 
observations, but certain irregularities have been omitted for 
the sake of simplicity. If we trace the line of surface tem- 
peratures, we observe that during the winter the water imme- 
diately under the ice stands substantially at 32° F., though it 
may be added that the ice itself often becomes much colder 
than 32° at its upper surface. As soon as the ice breaks up 
in the spring the temperature of the water begins to rise. 
This increase continues, with some fluctuations, until about 
the first of August. Cooling then begins and continues 
regularly through the autumn until the lake freezes in Decem- 
ber. If this curve of surface temperature were compared with 
the mean temperature of the atmosphere for the same period, a 
striking agreement would be noticed, and it would be seen that 
the water temperature is the higher of the two, — probably 
because of the direct heat received from the sun. In shallow 
ponds this effect is very marked, but in large, deep lakes, 
