beings found on the surface of the earth, which hide themselves in dark places, under the ground, etc., and are blind. Similar conditions prevail in the great deeps. There are blind crustaceans there, which probably live in the mud and under stones, while others, moving animals, fishes, have large, well-formed eyes. It must be that they see, or in other words that there is light there. Whether this light is produced in the depth by means of the phosphorescent organs which many of these animals, even fishes, possess, or whether it penetrates from above, as might perhaps be concluded from the fact that some of the deep-sea animals whose organization compels them to creep on the ground have yellow and red colors on their backs, is of no importance so far as our inquiry is concerned. We can only reach the inevitable conclusion that we see the colors of water not on a dark or black ground but on one that is illuminated, if but faintly. This is of moment because, in the light of it, particles floating in water are illuminated not from above only, but from below too.
We can satisfy ourselves of the effects of the coarser floating matter of sand and mud, as well as of the fact that the color of masses of water depends to a large extent upon the color of such matter. The Arve, which flows in front of my windows, is grayish yellow in summer, and opaque, assuming a deeper color after rain-storms; in winter, on the contrary, it is green, semi-transparent, and greener and clearer the less water it carries; facts easily explainable upon principles which one of my pupils nearly established by observations continued through a whole year. In summer the Arve carries, with the surplus glacier-water, grayish-yellow fragments of the mountain rocks in great multitudes; after heavy rains, masses of yellow mud are added to these, having been washed away from the banks of the stream. In winter the amount of sediment derived from the glaciers is small, and the blue color of the water is transformed into the green mixed color. Every glacial stream has its individual color, derived from the disintegrated rocks; and it is not without reason that the two rivers which join at Zweilütschine, in the Bernese Oberland, are known as the Black and the White Lütschine. The one brings disintegrated white limestone, the other the emery of pulverized dark slates.
How extraordinarily strong the mixed colors produced by sedimentary matter may appear was shown me by an observation which I made at Nice at the end of December, 1889. The weather had been fine for a few days, and the sea, which I overlooked from my window to Cape Antibes, about fifteen kilometres away, had been unusually blue. Now came stormy weather, with sporadic showers in the mountains of the Var. The river, whose mouth is about six kilometres from my house, poured considerable
