THE COLORS OF WATER. 253 



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 in- 

 quiry 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 be- 

 cause, 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 gray- 

 ish yellow in summer, and opaque, assuming a deeper color after 

 rain-storms ; in winter, on the contrary, it is green, semi-trans- 

 parent, 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, hav- 

 ing 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 Zweilutschine, in the Bernese Oberland, are 

 known as the Black and the White Lutschine. The one brings 

 disintegrated white limestone, the other the emery of pulverized 

 dark slates. 



How extraordinarily strong the mixed colors produced by sedi- 

 mentary 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 spo- 

 radic showers in the mountains of the Var. The river, whose 

 mouth is about six kilometres from my house, poured considerable 



