425 
The long period of low temperature during the winter of ’09-10 reduced 
the temperature of the water appreciably. 
In order to determine the difference in temperature between the water 
immediately under the ice and that near the bottom, the following simple 
apparatus was used. A large mouthed bottle with a glass stopper was 
laced firmly to a stick of convenient length and a cord was tied to the 
stopper. The bottle was lowered to the level desired and the stopper re 
moved by means of the cord. The bottle was thus filled with water of ap- 
proximately the same temperature as that surrounding it. The ther- 
mometer was then lowered into the bottie and the whole apparatus was 
made fast to the ice for about an hour. ‘The bottle with the thermometer 
in it was then raised and the reading made. The error resulting from this 
manipulation was very slight. The following readings were recorded: 
Jan. 11, 3 inches under ice, 2.2; near bottom, 3.1 C. 
Feb. 1, near surface, .8; near bottom, 2.8 C. 
Feb. 26, lower surface of ice, .i; near bottom, 1.3 C. 
These data indicate that after the pond is sealed with ice, the tem- 
perature of the water gradually approaches zero. ‘This lowering of the 
temperature and the establishment of a difference between the upper and 
lower strata is due to surface radiation. : 
Another condition which reduces the temperature of the water is the 
partial melting of the ice. As has been stated, the pond has Typha grow- 
ing in it near the edge. The Typha stems project through the ice all 
winter. When the ice begins to melt, the heat absorbed by these stems, 
melts holes through the ice around them. The pond then has a zone of 
openings at its periphery. On January 18, 1910, the ice was partially 
melted; five inches of solid ice remained. This was covered with four 
inches of water. The holes had formed around the Typha stems. <A stiff 
wind was blowing from the west. The result was a movement of water 
from west to east above the ice, and from east to west below the ice. As 
the temperature of the water above was approximately that of melting ice, 
its circulation below the ice must have lowered the temperature of the 
water. (See Fig. V.) 
Another factor which may have a slight influence on the temperature 
of the lower strata, is the decay of organic matter which covers the bot- 
tom. This, of course, goes on very slowly at low temperatures. 
