322 
WALDEN. 
I have been told that in the experiment at Cambridge 
to freeze water in a shallow wooden pond, though the 
cold air circulated underneath, and so had access to both 
sides, the reflection of the sun from the bottom more 
than counterbalanced this advantage. When a warm 
rain in the middle of the winter melts off the snow-ice 
from Walden, and leaves a hard dark or transparent 
ice on the middle, there will be a strip of rotten though 
thicker white ice, a rod or more wide, about the shores, 
created by this reflected heat. Also, as I have said, the 
bubbles themselves within the ice operate as burning 
glasses to melt the ice beneath. 
The phenomena of the year take place every day in 
a pond on a small scale. Every morning, generally 
speaking, the shallow water is being warmed more rap¬ 
idly than the deep, though it may not be made so warm 
after all, and every evening it is being cooled more rap¬ 
idly until the morning. The day is an epitome of the 
year. The night is the winter, the morning and even¬ 
ing are the spring and fall, and the noon is the summer. 
The cracking and booming of the ice indicate a change 
of temperature. One pleasant morning after a cold 
night, February 24th, 1850, having gone to Flints’ 
Pond to spend the day, I noticed with surprise, that 
when I struck the ice with the head of my axe, it re¬ 
sounded like a gong for many rods around, or as if I 
had struck on a tight drum-head. The pond began to 
boom about an hour after sunrise, when it felt the influ¬ 
ence of the sun’s rays slanted upon it from over the 
hills; it stretched itself and yawned like a waking man 
with a gradually increasing tumult, which was kept up 
three or four hours. It took a short siesta at noon, and 
boomed once more toward night, as the sun was with- 
