326 Sir Humphry Davy on the Colour of Water, fyc. 



which gives to it a greener hue. The Lake ofMerat, on the 

 contrary, which is fed from a lower country, and from less 

 pure sources, is grass green ; and there is an illustrative in- 

 stance in some small lakes fed from the same source in the 

 road from Inspruck to Stutgard, which 1 observed in 1815 

 (as well as I recollect), between Nazareit and Reiti. The 

 highest lake fed by melted snows in March when I saw it was 

 bright blue. It discharged itself by a small stream into ano- 

 ther, into which a number of large pines had been blown by a 

 winter storm, or fell in from some other cause ; in this lake its 

 colour was blue-green. In a third lake in which there were 

 not only pines and their branches, but likewise other decaying 

 vegetable matter, it had a tint of faded grass green ; and these 

 changes had occurred in a space of not much more than a mile 

 in length. These observations I made in 1815. On returning 

 to the same spot twelve years after, in August and September, 

 I found the character of the lakes entirely changed. The 

 pine wood washed into the second lake had disappeared ; a 

 large quantity of stones and gravel washed down by torrents, 

 or detached by an avalanche supplied their place ; there was no 

 perceptible difference of tints in the two upper lakes, but the 

 lower one, where there was still some vegetable matter, seemed 

 to possess a greener hue. 



The same principle will apply to the Scotch and Irish rivers, 

 which, when they rise or issue from pure rocky ravines, are 

 blue or bluish-green, and when fed from peat-bogs or alluvial 

 countries, yellow, or amber-coloured, or brown, even after 

 they have deposited a part of their impurities in great lakes. 

 Sometimes, though rarely, mineral impregnations give colour 

 to water : small streams are sometimes green or yellow from 

 ferruginous depositions. Calcareous matters seldom affect 

 their colour, but often their transparency, when deposited, 

 as is the case with the Velino at Terni, and the Anio at Ti- 

 voli ; but I doubt if pure saline matters, which are in them- 

 selves white, ever change the tint of water. 



The tint of the ocean probably depends on vegetable mat- 

 ters, and perhaps partially on two elementary principles, iodine 

 and brome, which it certainly contains, though these are pos- 

 sibly the results of decayed marine vegetables. These give a 



