On the Colour of the Atmosphere and Deep Water. 351 



the air, the sky is of a very variable blue, although the volume 

 of air be always the same ; and what renders it certain that its 

 blue colour is caused by these vapours is, that it appears black 

 when seen from the high eminences of the globe, above which 

 there is not sufficient vapour to reflect the blue. 



Limpid waters of sufficient depth reflect, like the air, a blue 

 colour from their interior ; it is of a darker shade, because it is 

 not intermingled with white rays ; frequently, indeed, it is not 

 perceptible, the reflection of the surface, in which the sky and 

 surrounding objects are painted as in a mirror, usually conceal- 

 ing the interior colour, or forming composite tints by combining 

 with it. 



We have seen that the property of producing colours pos- 

 sessed by the air, is owing to the presence of aqueous vapour; 

 and analogy may lead us to suppose, that the same property in 

 water is to be ascribed to its mixture with the air which it con- 

 tains. 



Although many causes, in general, conceal tlic blue colour 

 of waters, it is occasionally displayed in all its intensity ; of this 

 an example may be seen in the Rhone under the bridges of 

 Geneva, where the river seems to be composed of ultramarine. 

 The spectator is then in the most favourable situation for ob- 

 serving the colours of water, free from the reflection at its sur- 

 face, as far as is possible under an open sky. 



The agitation of the water, and the difference in the form of 

 the waves, produce a change in its colour ; sometimes the tran- 

 quil sea is seen to reflect the warm colours of the horizon, and 

 to represent all the tints of a bright sky so exactly, that the sea 

 and the sky seem to be confounded with each other ; . but if a 

 slight breeze ruffle the surface, the blue tints immediately suc- 

 ceed the brilliant tints in the places agitated ; all the inclined 

 surfaces of the small waves, which no longer reflect the heaven 

 to the eye of the spectator, permitting the interior colour of the 

 water to be seen through them. 



It is this which causes the water of the Rhone to be distin- 

 guished from those of the lake Leman ; the motion of the river 

 in the still waters of the lake must necessarily produce some de- 

 gree of agitation, and consequently diminish the brilliant reflec- 

 tion of the sky, and render the colour of the water more appa» 



