SPRING. 
321 
of Walden on the 6th of March, 1847, stood at 32°, or 
freezing point; near the shore at 33°; in the middle of 
Flints’ Pond, the same day, at 32J° ; at a dozen rods 
from the shore, in shallow water, under ice a foot thick, 
at 36°. This difference of three and a half degrees be¬ 
tween the temperature of the deep water and the shal¬ 
low in the latter pond, and the fact that a great propor¬ 
tion of it is comparatively shallow, show why it should 
break up so much sooner than Walden. The ice in the 
shallowest part was at this time several inches thinner 
than in the middle. In mid-winter the middle had been 
the warmest and the ice thinnest there. So, also, every 
one who has waded about the shores of a pond in sum¬ 
mer must have perceived how much warmer the water 
is close to the shore, where only three or four inches 
deep, than a little distance out, and on the surface where 
it is deep, than near the bottom. In spring the sun 
not only exerts an influence through the increased tem¬ 
perature of the air and earth, but its heat passes through 
ice a foot or more thick, and is reflected from the bottom 
in shallow water, and so also warms the water and melts 
the under side of the ice, at the same time that it is 
melting it more directly above, making it uneven, and 
causing the air bubbles which it contains to extend 
themselves upward and downward until it is complete¬ 
ly honey-combed, and at last disappears suddenly in a 
single spring rain. Ice has its grain as well as wood, 
and when a cake begins to rot or 66 comb,” that is, assume 
the appearance of honey-comb, whatever may be its 
position, the air cells are at right angles with what was 
the water surface. Where there is a rock or a log rising 
near to the surface the ice over it is much thinner, and 
is frequently quite dissolved by this reflected heat; and 
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