440 071 the Causes of the Colour 



the colours in question.* We know that the icebergs of 

 the polar seas are frequently of an emerald green f, and 

 the glaciers J of the Alps are of a green or a deep blue, 

 and that the waters from them issue of a pale blue colour. 

 As Mrs. Somerville has observed in her recent work 

 On the Connexion of the Sciences (p. 174'.), it is on the 

 property of unequal absorption that " the colours of trans- 

 parent media depend ; for they also receive their colour from 

 their power of stopping or absorbing some of the colours of 

 white light and transmitting others." This, however, J. R. 

 seems aware of, in part. 



Mr. De la Beche has some remarks on the coloured waters 

 of different seas, quoting Sir Gore Ouseley, in which green 

 and blue water are alluded to. (Geological Manual, 1st ed. 

 p. 89, 90.) All lakes are more or less coloured, even when 

 most pellucid. There is a lake on the summit of Blencathra 

 or Saddleback Mountain, in Cumberland, the deep waters of 

 which are quite black to look upon, and it is said that they 

 reflect the stars in the daytime ; which, by the way, I could 

 never observe, though frequently looking for them. The most 

 perfectly clear expanse of water in England is Derwent- 



* The Rliine, from the Alps to the Lake of Constance, is blue ; after- 

 wards grass green ; then, after having received the waters of the Black 

 Forest and Alsace, yellowish green. The Maine, traversing the red sand- 

 stones of Franconia, takes a yellowish red tint, but in very cold seasons it 

 becomes greenish blue by the precipitation of the oxide of iron ; it is amber 

 grey when it is not coloured yellow by long rains. All the rivers of Ba- 

 varia Proper are bluish green in winter, grass green in spring, and pale 

 grass green in autumn. (Keiv Edin. P/iiL Journ.^ Jan. 1830, p. 193.) 

 Sir H. Davy (in his Salmonla) says, the colour of snow water is deep 

 ])lue ; that the green tinge comes from the vegetables that grow on the 

 banks ; and the yellow and brown, from turf; and that the green hue of 

 the sea is derived from vegetable matter, iodine, and bromium. He re- 

 lates some experiments with iodine on the ice of the glaciers. 



\ On the colour of icebergs, see Scoresby's Arctic Regions^ i. 254. 

 The glacier of Rosboden in Switzerland, is all through of a dark blue : 

 but green is a general colour. 



' J It must be observed, that the ice of the glaciers is very different 

 from common ice. It consists of snow which has been melted, frozen, and 

 compressed, perhaps, a thousand times ; till it has become solid, hard, and 

 often as compact as marble. I have frequently seen, at Geneva, cubes of 

 alpine ice upon the table, used to cool the wine in the drinking-glasses. 

 It may be also remarked, that it is in the warm months of the year that 

 the ice of the previous colder season is generally subjected to the pro- 

 cesses alluded to; that, in those months, avalanches occur; and that the 

 alpine rivers, contrary to what occurs in colder localities, are most swoln 

 with the waters arising from melted ice and snow. There are, however, 

 certain seasons when, as in 1816, winter seems to extend throughout the 

 year. It is asserted, by an observer, that not a single week, in 1816, passed 

 without a fall of snow on Mont St. Bernard. I shtill produce the quotation 

 in another place. 



