Page:Walden, or, Life in the Woods.djvu/270

beneath. I sometimes used to cast on stones to try the strength of the ice, and those which broke through carried in air with them, which formed very large and conspicuous white bubbles beneath. One day when I came to the same place forty-eight hours afterward, I found that those large bubbles were still perfect, though an inch more of ice had formed, as I could see distinctly by the seam in the edge of a cake. But as the last two days had been very warm, like an Indian summer, the ice was not now transparent, showing the dark green color of the water, and the bottom, but opaque and whitish or gray, and though twice as thick was hardly stronger than before, for the air bubbles had greatly expanded under this heat and run together, and lost their regularity; they were no longer one directly over another, but often like silvery coins poured from a bag, one overlapping another, or in thin flakes, as if occupying slight cleavages. The beauty of the ice was gone, and it was too late to study the bottom. Being curious to know what position my great bubbles occupied with regard to the new ice, I broke out a cake containing a middling sized one, and turned it bottom upward. The new ice had formed around and under the bubble, so that it was included between the two ices. It was wholly in the lower ice, but close against the upper, and was flattish, or perhaps slightly lenticular, with a rounded edge, a quarter of an inch deep by four inches in diameter; and I was surprised to find that directly under the bubble the ice was melted with great regularity in the form of a saucer reversed, to the height of five eighths of an inch in the middle, leaving a thin partition there between the water and the bubble, hardly an eighth of an inch thick; and in many places the small bubbles in this partition had