560 bulletin of the bureau of fisheries. 
Table VIII. — Calories per Square Centimeter of Surface Required to Raise Temperature 
OF Water of Lake from Zero to Summer Temperature. 
Lakes. 
Dm. 
meters. 
Tm« 
1910. 
Calories 
1910. 
Tm« 
1911. 
Calories 
1911. 
38.8 
54 - S 
30 - 5 
29-3 
88.6 
43-5 
33 - I 
11.07 
9. 26 
12. 17 
13 - 59 
7.71 
10. 10 
11.90 
43*000 
50. 000 
37*000 
40.000 
68.000 
44.000 
39.000 
9.99 
8 . 94 
zz. 48 
12. 86 
7-35 
10. 84 
11.42 
39.000 
49.000 
35.000 
38.000 
65.000 
47.000 
38.000 
Keuka 
It will be seen that the order of the lakes is substantially the same in each year 
and that the order is that of their depth, as was the case also with their mean tempera- 
tures. Keuka, Owasco, and Green Lakes, whose depths are nearly the same, are very 
close in the amount of heat which they have received. Keuka Lake is the lowest in 
both years, a result due, like the thinness of the epilimnion, to its sheltered position. 
This result represents what may be called the gross heat budget. It can be readily 
computed but it is of very little value since it does not represent any actual gains of 
heat. The winter temperature is never as low as zero, and other things being equal, it 
will be higher in the case of the deeper lake. The most important fact to be known is 
the annual heat budget of the lake — the amount of heat necessary to raise its water 
from the winter to the summer temperature — and to determine this we must know 
both the minimum and the maximum temperature of the water. In case of a lake whose 
surface freezes, the minimum temperature is that at the time of freezing, although in 
case of a large lake no great error would result from using any temperature taken during 
the ice period. In case of a lake that does not freeze, the date and value of the minimum 
temperature can be ascertained only by a study of the lake during the winter, but a 
series taken in February will not be far wrong. Such observations were made on four 
of these lakes in the winter of 1910-11 and two in the winter of 1911-12, with the 
results shown in the following table. The minimum temperature derived from obser- 
vations taken in a single winter may be compared with the temperature both of the 
preceding and following summer; and thus two results can be obtained from three sets 
of observations. This method has been followed in the table. 
Table IX. — Difference Between Summer and Winter Temperatures of the Several Lakes. 
[Annual heat budgets stated in gram-calories per square centimeter of the surface of the lake.] 
Lakes. 
Dm 
meters. 
Tm- 
1910. 
Tm^ 
1911. 
Tm« 
1911. 
Tmw 
1912. 
Tm^ 
1912. 
Tm- 
1910 
minus 
Tm^ 
1911. 
Calo- 
ries. 
Tm» 
191Z 
minus 
Tm^ 
1911. 
Calo- 
ries. 
Tm" 
1911 
minus 
Tm"' 
1912. 
Calo- 
ries. 
Tm- 
1912 
minus 
Tm^ 
Z912. 
Calo- 
ries. 
54-5 
29-3 
88.6 
43 - 5 
33 - I 
9. 26 
13 - 59 
7. 71 
10. 10 
11. 90 
2.23 
•83 
3-39 
I. 10 
2.13 
8.94 
12. 86 
7-35 
10. 84 
11. 42 
7-03 
le. 76 
4-32 
9. 00 
9 - 77 
38. 200 
38,900 
38,300 
39* 200 
32. 200 
6. 71 
12.03 
3-96 
9 - 74 
9. 29 
36, 500 
36. 600 
35* 100 
42, 400 
30. 600 
1-49 
13-93 
11.37 
34 * 700 
12.44 
37 . 900 
Skaneateles 
Green (Wis.). . 
2-39 
I. 74 
®IO. 21 
II. 96 
8 . 45 
9. 68 
36,800 
31,900 
® 7. 82 
10. 22 
034,000 
33 ) 800 
a Taken Oct. i8. and therefore below Tm*. See p. 565. 
