428 



The lon^: period of low temperature during tlie winter of '09-'10 reduced 

 tlie 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 bottle 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. 13, 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, .1 ; 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 Januai'y 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 temiierature 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. g<jes on very slowly at low temperatures. 



