546 bulletin of the bureau of fisheries. 
TEMPERATURES, 
general observations. 
Temperature observations were made in these lakes on the following dates: 
Lake. Date of observations. 
Canadice Aug. 24, 1910. 
Canandaigua Aug. 20, 1910; Sept. 4, 1911. 
Cayuga Aug. ii, 1910; Feb. 13, Sept. 2, 1911. 
Conesus Aug. 25, 1910. 
Hemlock Aug. 23, 1910. 
Keuka Aug. 18, 1910; Sept. 5, 1911. 
Otisco Aug. 16, 1910. 
Owasco Aug. 13, 1910; Feb. ii, Sept. 3, 1911; Mar. i, Sept. 13, 1912.0 
Seneca Aug. 2, 3, 4, 7, 9, 1910; Feb. 10, Sept, i, 1911. 
Skaneateles Aug. 15, 1910; Feb. ii, Sept. 3, 1911; Mar. 7, Oct. 15, 1912.® 
The details of the observations are given in the tables of the appendix (p. 601). It 
will be seen that in all of the lakes temperatures were taken in August, 1910, and in four 
of the lakes series of temperatures were taken only at that time. Two other lakes were 
visited also in early September, 1911. Four others were visited in both summers and 
in February, 1911, and two of these also in March, 1912, and in the fall of that year. 
The attempt was made to secure series of temperatures which would show approximately 
the maximum summer temperature of the water, and in the case of those visited in the 
winter, the minimum temperature also. The most important conclusions to be drawn 
from the observations, as will be shown later, concern the annual heat budget of the 
lakes and the distribution of the heat in summer. 
The study of the New York lakes was made in order to test in larger bodies of water 
the principles of lake temperatures established for the inland lakes of Wisconsin. Since 
the phenomena of the Finger Lakes exactly conform to these principles, we have not 
hesitated to use them as illustrations of these laws, though we should not have deduced 
the laws from them alone. The full discussion of these underlying principles belongs 
to the report on lakes of Wisconsin now under preparation, but several of them are 
briefly discussed in connection with this report. 
The following principles are therefore assumed as demonstrated for lakes in the 
general climatic and topographic situation of the Finger Lakes. It is not asserted that 
they hold for lakes situated under other conditions. 
I . Every deeper lake has an equithermal period of several weeks in summer, cover- 
ing as a maximum August and parts of late July and early September, during which 
the daily gains and losses of heat nearly balance, when the mean temperature of the lake 
is substantially constant, and when the epilimnion has a nearly constant thickness. A 
series of observations taken on one day during this period gives a good idea of the 
general temperature condition of the lake during the whole period. 
The observations of 1912 were made by Mr. J. W. Ackermann, superintendent of water works, Auburn, whose kind assist- 
ance is herewith acknowledged. 
