The frozen surface of Walden Pond, seen near at hand, has a green tint but at a distance is beautifully blue, says Henry David Thoreau, the literary hermit who settled near Concord, Massachusetts and described the stillness of his life in the book Walden; or, Life in the Woods (1854). The stillness has been interrupted by 100 labourers cutting the ice for commercial harvest and the colour presents a puzzle.
“You can easily tell it from the white ice of the river, or the merely greenish ice of some ponds, a quarter of a mile off. Sometimes one of those great cakes slips from the iceman’s sled on to the village street and lies there for a week like a great emerald, an object of interest to all passers.
I have noticed that a portion of which in the state of water was green will often, when frozen, appear from the same point of view blue. So the hollows about this pond will, sometimes, in the winter, be filled with a greenish water somewhat like its own, but the next day will have frozen blue.
Perhaps the blue colour of water and ice is due to the light and air they contain, and the most transparent is the bluest.” He watched from his window for 16 days as teams of men and horses gathered the ice.
“And now they are all gone, and in 30 days more, probably, I shall look from the same window on the pure, sea-green Walden water there, reflecting the clouds and the trees, and sending up its evaporations in solitude, and no traces will appear that a man has ever stood there.”
