Professor Bunson on the Colvur of Water. 97 



the sombre volcanic rocks obstruct the reflection of the inci- 

 dent light. It will, therefore, easily be understood that it is 

 onl\' where these disturbing iuHuences do not exist that the 

 colour of the water will be seen in all its beauty. Amongst the 

 places at which this requirement is most completely fulfilled, 

 we may especially instance the Blue Grotto at Capri, in the 

 Gulf of Naples. The sea is there most remarkably clear to a 

 very great depth, so that the smallest objects may be dis- 

 tinctly seen on the light bottom at a depth of several hundred 

 feet. All the light that eaters the grotto, the entrance of 

 which is only a few feet above the level of the sea, in the 

 precipitous rock opening upon the surface of the water, must 

 penetrate the whole depth of the sea, probably several hun- 

 dred feet, before it can be reflected into the grotto from the 

 clear bottom. The light acquires, by these means, so deep 

 a blue colouration from the vast strata of water through which 

 it has passed, that the dark walls of the cavern are illumined 

 by a pure blue radiance, and the most differently coloured 

 objects below the surface of the water are made to appear 

 bright blue. 



An equally remarkable example of this fact presents itself 

 in the glaciers of Iceland, as well as in those of Switzerland, 

 which shews that water does not lose its original colour even 

 when in a solid condition. At the distance of many miles, 

 the eye may distinguish, on the flat heights of the " JokuU," 

 the boundaries that separate the bluish ice of the glaciers 

 from the white inaccessible plains of snow that rise to the 

 summit of these mountains. On a closer examination of these 

 glaciers, one is surprised to observe the purity and transpa- 

 rency of the ice, which often appears to be wholly free in large 

 masses from vesicles of air and foreign admixtures, whilst its 

 vast fissures and cavities are coloured all shades, from the 

 lightest to the darkest blue, according to the thickness of the 

 strata through which the light has penetrated. 



The blue tint of the cloudless and vapoury atmosphere is 

 jirobably dependent on similar phenomena, if we are justified 

 in concluding, from the colour of solid and fluid water, that 

 aqueous vapour has a similar colour. On considering all 

 these facts, we can scarcely doubt for a moment that the blue 



VOI,. XFA'II. NO. Xf'III. — .ItTIA' 1849. O 



