A LIMNOLOGICAIv STUDY OF THE FINGER LAKES. 575 
as much work as that which was actually available for warming it. This is obviously 
a demand impossible to satisfy. 
Thus the shallow lake has a double disadvantage. Its smaller reduced thickness 
for any given stratum diminishes the volume of water into which heat may be distributed 
from the surface. This deficiency of volume can not be compensated by an equivalent 
rise of temperature, since the amount of energy present to mix the water is soon ex- 
hausted by the rapid rise of thermal resistance to mixture as the temperature increases. 
The shallow lake has an advantage in one respect, probably a small advantage but 
one whose amount has not been determined. What may be called its mixing areas are 
more efficient because of the gradual slope of the bottom. Consider the condition of the 
lake with direct thermal stratification, whose form is that of an oblong tank with vertical 
sides. A wind blowing the surface water to one end would depress the isotherms there. 
The cold water would swing back and oscillate, but there would be very little friction 
between the strata and little mixture and correspondingly little warming of the lower 
water. In an actual lake with sloping bottom, the narrower ends concentrate and give 
force to the movements of the water caused by the wind and increase the amount of 
mixture due both to the direct and indirect effects of the wind. As the warm water is 
forced downward at the ends, it squeezes out the cooler water in a relatively thin layer 
between the descending surface of the epilimnion and the gradually sloping bottom of 
the lake. As the cool water swings back, its edge pushes in like a wedge between the 
bottom and the epilimnion. Both movements are attended with relatively great fric- 
tion and corresponding mixture of the warmer and cooler water. Thus the ends of the 
lake constitute its chief mixing areas, and they are the region where the gradual warming 
of the thermocline and hypolimnion goes on most rapidly. Relatively little warming is 
effected in the open water of the lake or on its steep sides where movement, which is 
chiefly lateral, is attended with little resistance and consequent mixture. In this respect, 
therefore, the shallow lake has an advantage over the deeper one whose slopes are steeper. 
The shallowness of the water is also an advantage in the spring before the thermocline 
is formed, in that the water is nearer the surface and so more readily accessible to the 
influence of the wind. Thus its temperature rises above that of the deeper lake, but it 
never reaches a point, under conditions otherwise equal, high enough to give it as great 
a total amount of heat per unit of surface as the deeper lake accumulates. 
Table; XIV. — Extent, Reduced Thickness, and Heat Supply of the Thermal Regions op 
Canadice and Otisco Lakes. 
Rep: ion. 
Extent, 
meters. 
R. T. 
meters. 
Tm«-4. 
Calories. 
Per cent. 
Canadice Lake, 1910. 
Epilimnion 
0-7 
6-33 
18. 2 
11,500 
58.8 
Thermocline 
7-12 
3- 76 
12. 9 
4, 800 
24. 8 
Hypolimnion 
12--25 
6.28 
4-93 
3, 100 
16. 2 
Otisco Lake, 1910. 
Epilimnion 
0-7 
5- 57 
18.8 
10, 500 
62. 7 
Thermocline 
7-12 
3-05 
13- 2 
4, 000 
24. 1 
Hypolimnion 
I2'~20 
2.58 
8.4 
2,200 
12.3 
