瓦尔登湖: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.
掘冰人的大量挖掘，通常使得一个湖沼的冰解冻得早一些；因为即使在寒冷的气候中，给风吹动了的水波，都能够消蚀它周围的冰块。可是这一年，瓦尔登没有受到这种影响，因为它立刻穿上了新的一层厚冰，来替代那旧的一层。这一个湖，从不像邻近的那些湖沼的冰化得那样早，因为它深得多，而且底下并没有流泉经过，来溶化或耗损上面的冰。我从没有见它在冬天里爆开过；只除了一八五二――一八五三年的冬季，那个冬季给许多湖沼这样严重的一次考验。它通常在四月一口开冻，比 灵特湖或美港迟一星期或十天，从北岸，和一些浅水的地方开始，也正是那里先行冻结起来的。它比附近任何水波更切合时令，指示了季节的绝对进度，毫不受温度变幻不定的影响。三月里严寒了几天，便能延迟其他湖沼的开冻日了，但瓦尔登的温度却几乎没有中断地在增高。
一八四七年三月六日，一只温度表插入瓦尔登湖心，得三十二度，或冰点，湖岸附近，得三十三度；同日，在弗灵特湖心，得三十二度半；离岸十二杆的浅水处，在一英尺厚的冰下面，得三十六度。后者湖中，浅水深水的温度相差三度半，而事实上这一个湖大部分都是浅水，这就可以说明为什么它的化冰日期要比瓦尔登早得多了。那时，最浅水中的冰要比湖心的冰薄上好几英寸。仲冬，反而是湖心最温暖，那儿的冰最薄。同样，夏季里在湖岸附近，涉水而过的人都知道的，靠湖沼的水要温暖得多，尤其是只三、四英寸水的地方，游泳出去远了一点，深水的水面也比深水深处温暖得多。而在春天，阳光不仅在温度逐渐增加的天空与大地上发挥它的力量，它的热量还透过了一英尺或一英尺以上的厚冰，在浅水处更从水底反射到上面，使水波温暖了，并且溶化了冰的下部，同时从上面，阳光更直接地溶化了冰，使它不均匀了，凸起了气泡，升上又降下，直到后来全部成了蜂窝，到最后一阵春雨，它们全部消失。冰，好比树木一样，也有纹理，当一个冰块开始溶化，或蜂窝化了，不论它在什么地位，气泡和水面总是成直角地相连的。在水面下有一块突出的岩石或木料时，它们上面的冰总要薄得多，往往给反射的热力所溶解；我听说，在剑桥曾有过这样的试验，在一个浅浅的木制的湖沼中冻冰，用冷空气在下面流过，使得上下都可以发生影响，而从水底反射上来的太阳的热量仍然可以胜过这种影响。当仲冬季节下了一阵温暖的雨，溶解了瓦尔登湖上带雪的冰，只在湖心留着一块黑色而坚硬的透明的冰，这就会出现一种腐化的，但更厚的自冰，约一杆或一杆多阔，沿湖岸都是，正是这反射的热量所形成的。还有是我已经说起过的，冰中间的气泡像凸透镜一样从下面起来溶解冰。
这一年四季的现象，每天在湖上变化着，但规模很小。一般说来，每天早晨，浅水比深水温暖得更快，可是到底不能温暖得怎样，而每天黄昏，它却也冷得更快，直到早晨。一天正是一年的缩影。夜是冬季，早晨和傍晚是春秋，中午是夏季。冰的爆裂声和隆隆声在指示着温度的变化。一八五0年二月二十四日，一个寒冷的夜晚过去后，在令人愉快的黎明中，我跑到 灵特湖去消磨这一天，惊异地发现我只用斧头劈了一下冰，便像敲了锣一样，声音延展到好几杆远，或者也可以说，好像我打响了一只绷得紧紧的鼓。
太阳升起以后大约一个小时，湖感受到斜斜地从山上射下来的阳光的热力了，开始发出隆隆的声响；它伸懒腰，打呵欠，像一个才醒过来的人，闹声渐渐越来越响，这样继续了三四个小时。正午是睡午觉的时候，可是快到傍晚的时候，太阳收回它的影响，隆隆声又响起来了。在正常的天气中，每天，湖发射了它的黄昏礼炮，很有定时。只是在正午，裂痕已经太多，空气的弹性也不够，所以它完全失去了共鸣，鱼和麝鼠大约都不会听到而被震动得呆住的。渔夫们说，“湖的雷鸣”吓得鱼都不敢咬钩了。湖并不是每晚都打雷的，我也不知道该什么时候期待它的雷鸣，可是，虽然我不能从气候中感到什么不同，有时还是响起来了。谁想得到这样大，这样冷，这样厚皮的事物，竟然这样的敏感？然而，它也有它的规律，它发出雷声是要大家服从它，像蓓蕾应该在春天萌芽一样。
周身赘疣的大地生机蓬勃。对于大气的变化，最大的湖也敏感得像管往中的水银。
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