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Spring
The opening of large tracts by the ice…cutters commonly causes a
pond to break up earlier； for the water； agitated by the wind； even
in cold weather； wears away the surrounding ice。 But such was not
the effect on Walden that year； for she had soon got a thick new
garment to take the place of the old。 This pond never breaks up so
soon as the others in this neighborhood； on account both of its
greater depth and its having no stream passing through it to melt or
wear away the ice。 I never knew it to open in the course of a
winter； not excepting that of '52…3； which gave the ponds so severe
a trial。 It commonly opens about the first of April； a week or ten
days later than Flint's Pond and Fair Haven； beginning to melt on
the north side and in the shallower parts where it began to freeze。
It indicates better than any water hereabouts the absolute progress
of the season； being least affected by transient changes of
temperature。 A severe cold of a few days duration in March may very
much retard the opening of the former ponds； while the temperature
of Walden increases almost uninterruptedly。 A thermometer thrust
into the middle of Walden on the 6th of March； 1847； stood at 32x；
or freezing point； near the shore at 33x； in the middle of Flint's
Pond； the same day； at 32＋x； at a dozen rods from the shore； in
shallow water； under ice a foot thick； at 36x。 This difference of
three and a half degrees between the temperature of the deep water
and the shallow in the latter pond； and the fact that a great
proportion 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
midwinter the middle had been the warmest and the ice thinnest
there。 So； also； every one who has waded about the shores of the
pond in summer 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 temperature 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
completely honeycombed； 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 〃comb；〃 that is； assume the appearance of
honeycomb； 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 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 rapidly than the deep； though it may not be
made so warm after all； and every evening it is being cooled more
rapidly until the morning。 The day is an epitome of the year。 The
night is the winter； the morning and evening 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 Flint's Pond to
spend the day； I noticed with surprise； that when I struck the ice
with the head of my axe； it resounded 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 influence 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
withdrawing his influence。 In the right stage of the weather a pond
fires its evening gun with great regularity。 But in the middle of
the day； being full of cracks； and the air also being less elastic；
it had completely lost its resonance； and probably fishes and
muskrats could not then have been stunned by a blow on it。 The
fishermen say that the 〃thundering of the pond〃 scares the fishes
and prevents their biting。 The pond does not thunder every evening；
and I cannot tell surely when to expect its thundering； but though I
may perceive no difference in the weather； it does。 Who would have
suspected so large and cold and thick…skinned a thing to be so
sensitive？ Yet it has its law to which it thunders obedience when
it should as surely as the buds expand in the spring。 The earth is
all alive and covered with papillae。 The largest pond is as
sensitive to atmospheric changes as the globule of mercury in its
tube。
One attraction in coming to the woods to live was that I should
have leisure and opportunity to see the Spring come in。 The ice in
the pond at length begins to be honeycombed； and I can set my heel
in it as I walk。 Fogs and rains and warmer suns are gradually
melting the snow； the days have grown sensibly longer； and I see how
I shall get through the winter without adding to my wood…pile； for
large fires are no longer necessary。 I am on the alert for the
first signs of spring； to hear the chance note of some arriving
bird； or the striped squirrel's chirp； for his stores must be now
nearly exhausted； or see the woodchuck venture out of his winter
quarters。 On the 13th of March； after I had heard the bluebird；
song sparrow； and red…wing； the ice was still nearly a foot thick。
As the weather grew warmer it was not sensibly worn away by the
water； nor broken up and floated off as in rivers； but； though it
was completely melted for half a rod in width about the shore； the
middle was merely honeycombed and saturated with water； so that you
could put your foot through it when six inches thick； but by the
next day evening； perhaps； after a warm rain followed by fog； it
would have wholly disappeared； all gone off with the fog； spir