44f Causes of the Colour of the Rhone a7id Rhine. 



From the summit of Skiddaw, in a very clear day, I once 

 saw, very distinctly marked, all the sandbanks in the Solway 

 Frith, by the yellowness of the water above them. This 

 arose from the reflection and shallowness of the water. 



Stanley GreeJiy Aprils. 1834. W. B. Clarke. 



Causes of the Colour of the Water of the Rhone and Rhine, 

 The Rhone, at Geneva, is some 17 ft. deep, but so exqui- 

 sitely clear that a pebble may be seen in the bottom at that 

 depth ; but, seen with its surface at a small angle, to the eye 

 it appears of the most beauteous transparent blue. This, 

 some assert, arises from the lake's waters being actually co- 

 loured ; but the transparency of the waters en ?72«55^ disproves 

 this. The fact is, it arises from the colour of the bottom, 

 which, being of the same substance as the neighbouring side 

 of Jura, a calcareous tufa, is nearly white ; and the blue of 

 the sky is thus reflected with such singular beauty. {Robert 

 Mallet^ Esq., CapelStreet, Dublin; in Gard, Mag., viii. 526.) 



Mr. Mallet mistakes, I think, in two points. The side of 

 the Jura is not " a calcareous tufa ; " nor is the bottom of the 

 channel under the bridge at Geneva so "nearly white" as he 

 states. The bottom is strewed with stones, broken pots, &c. ; 

 and there is also an alluvial coat of mud, not, perhaps, very 

 thick, but still sufficiently so to resist the current. Had the 

 bottom been " nsohite^^ or " nearly white," the colour of the 

 water would be green, and not blue. I would refer Mr. 

 Mallet and J. R., upon this fact, to the very instructive and 

 elaborate treatise of De Maistre, in the Bibliotheque Uni- 

 verselle (an accurate translation of which, by Professor Gris- 

 com, is published in the American Journal of Science and Arts 

 for April, 1834*); in which treatise, actual experiment is 

 brought forward to show that "white substances at the bot- 

 tom of blue 'water reflect green light. The count alludes, in 

 his paper, to the Rhone and the Rhine, to the green and blue 

 tints of the glaciers, and to the colours of the sea near the 

 shore and in deep places ; and introduces some discussion on 

 the blueness of the sky and of the veins in the human body, 

 and on the properties of mixed colours to reflect the blue 

 rays. By far the most instructive account which I have seen 

 is also there given of the singular grotto at Capri, called 

 the Azure Grot; the description of which might, with good 

 effect, be transferred to the pages of this Magazine. That 

 description would be particularly illustrative of J. R.'s en- 



* " On the Colour of the Air and of deep Waters, and on some other 

 analogous fugitive Colours," by Count Xavier dc Maistre. 



