So you go on, and ever on. It is not wise to retrace your strokes, for those ice crystals that gave to let you through and then gripped one another again to hold you up may not withstand a second impact; nor is it wise to stop. Mass and motion have given you momentum and you have acquired some of the obscure stability of the gyroscope. You tend to stay on your plane of motion, though the ice itself has strength to hold only part of your weight. Thus the wild duck, threshing the air with mighty strokes, glides over it, held up by the same obscure force. The ice has no time to break and let you through. You are over it and onto another bit of uncracked surface before it can let go. The day warmed a little with a clear sun but the frost that night bit deep again and the next morning the ice had nearly doubled in thickness and would not crack under any strain which my weight could put upon it. A second freezing, even though both be thin, gives a stronger ice than a single freezing of equal depth, just as the English bowmaker of the old days used to glue together a strip of lancewood and a strip of yew, or even two strips of the same wood, thus making a far stiffer bow than one made of a single piece of equivalent dimensions. This ice was much smoother too. That evaporation which is steadily going on from the surface of ice even in the coldest weather, the crystals passing to vapor without the intervening stage of water, had worn off the embossing. The ice instead of being black was gray with countless air bubbles all through its texture. You will always find these after a day’s clear sun on a first freezing. I fancy the ice crystals make minute burning glasses under the sun’s rays and thus cause tiny meltings within its own bulk, the steam of the fusing making the bubbles; or it may be that the air with which the north wind of two days before had been saturating the water was thus escaping from solution. It was midday of this second day of skating weather before I reached the pond. The sky was overcast, the wind piped shrill again, and there were snow-squalls about. The pond was empty and lone. I thought no living creature there beside myself, and it was only at the second call of a familiar voice that I believed I heard it. Then, indeed, I stopped and listened up the wind. It came again, a wild and lonely whistle that was half a shout, beginning on the fifth of the scale, sliding to the top of the octave, and then to a third above, and I heard it with amazement. The pond was firmly covered with young ice. Why should a loon be sitting out on it and hooting to me?