48 TRANSLATIONS AND SELECTED ARTICLES. 
similar circumstances, which the mariner can recognize, and even pre- 
dict from that aspect. 
I permit myself a remark as to the place in which the green colour 
of water arises. The Tegernsee receives its water by several supplies, 
among which the Weissach and the Rottach are the most considerable. 
After lengthened dry weather, the bed of the Weissach is quite 
empty ; the pebbles which cover the bottom are quite dry, and almost 
white. After atime of such weather, I went up the course of the 
Weissach in order to observe the first water which moistened the 
ground. This water could have no other origin than the atmosphere. 
Yet the first quantity, which was sufficient to look through in bending 
over the bed, immediately appeared green. Hence the humic acid 
salts must have been already formed in the bed of the river, and are 
only dissolved by the water; it is not necessary to assume that the 
springs which fed the rivers must bring an alkaline solution which 
shall afterwards dissolve the humic acid. 
Water, of atmospheric origin, in its purest condition of ice and 
snow is also blue. The glaciers of the Alps and of Iceland also show 
this colour when the adjacent waters, which in part arise from the 
glacier streams, are green. H. and A. von Schlagintweit estimate the 
colour of glacier-ice in the crevices as being equal to the mixed colour 
shown by a colour circle on which 74-9 parts of white, 24-3 of cobalt 
blue, and 0-8 part of green were painted. Osann saw that the light 
in a hole in the mountain snow about two feet deep was blue, and be- 
lieved that this colour was due to the blue colour of the air, which 
has a deeper blue in the upper than in the under layers, and he there- 
fore thinks that the blue colour of glacier-ice is heightened by that of 
the air in those higher regions. But the experiment on which he de- 
pends succeeds with freshly fallen snow on the plain as well as above 
the snow-line. The other colour depends on the colour of the small 
erystals of ice which the light repeatedly reflected backwards and 
forwards in such a small hole must traverse. Green ice can only be 
caused by the freezing of green lakes and rivers; the atmospheric 
fall, and the compression of the high snow can only give rise to the 
formation of blue ice. 
Erlangen, December, 1861. 
