ON THE COLORS OF WATER. 69 



nature the seas, lakes, and rivers we shall receive a different im- 

 pression. In these, the water not only appears colored, but of various 

 colors, and of a rich diversity of shades. The Mediterranean is of a 

 beautiful indigo, the ocean is sky-blue, the Lake of Geneva is cele- 

 brated for its lovely and transparent azure waters ; the Lake of Con- 

 stance and the Rhine, the Lake of Zurich and the Lake of Lucerne, 

 have waters quite as transparent, but rather green than blue ; and the 

 green waters of the little Lake of Kloenthal, near Glaris, can hardly be 

 distinguished from the surrounding meadows. Other waters are of a 

 darker color, like those of the Lake of Staffel, at the foot of the Bava- 

 rian Alps, which was quite black the day I saw it, though clear in 

 shallow places. 



These facts start the questions whether water, after all, has not a 

 color ; if it has, what the color is, and what causes the varied tints 

 under which it is seen. The solution of these questions has long oc- 

 cupied the minds of scientific inquirers, and it can not yet be said 

 that they have been answered. Disagreement still prevails respecting 

 them. 



M. Durocher, in his " Studies of the Glaciers of Northern and Cen- 

 tral Europe," has expressed the opinion that the bine color of some 

 waters is of glacial origin, and that it is so peculiar to water from 

 snow-fields and glaciers as to constitute a mark by which to distinguish 

 whence it has proceeded. " If the color of water is really blue," he 

 adds, " the substitution for it of gray or greenish tints proceeds in the 

 majority of cases from organic substances, chiefly vegetable rather 

 than animal." 



M. Durocher's view is disputed by M. Th. Martins, who points to 

 the snow-fed Lakes of Sioron and the Bachalpsee, as one azure blue, 

 the other yellowish green, and the Lake of Brienz, whose yellowish- 

 green waters, after crossing the Isthmus of Interlachen, become blue in 

 the Lake of Thun. 



Bunsen was the first one to deny, with any real knowledge, the 

 absence of color in water. Struck with the green-blue color of the 

 hot water of the Icelandic geysers, he examined pure water in a tube, 

 found it blue, and concluded that that was the true color of the liquid, 

 while other colors observed were derived from foreign matters or by 

 reflection from a colored bottom. 



Tyndall, Soret, and Hagenbach took up the question about twenty 

 years after Bunsen. Tyndall found by experiments on polarization 

 that the blue of the atmosphere was caused by reflection of the shorter 

 blue light-waves at the expense of the longer waves, from particles of 

 aqueous vapor in an extreme state of division, which he called nascent 

 cloud. If the particles were larger, longer waves would be reflected, 

 and the color would approach white. Soret, seeking to learn if the 

 blue color of the Lake of Geneva had not an analogous origin, applied 

 the polarization experiments to it, and concluded that it contained 



