Place upon the surface of snow, as upon the window-sill, in bright
daylight or sunshine, pieces of cloth of the same size and quality, but
of different colours, black, blue, green, yellow, and white: the black
cloth will soon melt the snow beneath it, and sink downwards; next the
blue, and then the green; the yellow but slightly; but the snow beneath
the white cloth will be as firm as at first.