224 M. W. Beetz on the Colour of Water. 



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 hy 

 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 a time 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 

 Schlagintweitf estimate the colour of glacier-ice in the crevasses 

 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 08 part of 

 green were painted. Osann J saw that the light in a hole in the 

 mountain snow about two feet deep was blue, and believed 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 

 therefore 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 depends 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 crystals 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. 



* Bunsen, loc. cit. p. 47. 



f Phys. Geogr. der Alpen, i. page 22. 



X Verh. d. Wiirzb. Ges., iv. 231. 



