Professor Forbes on the Colours of the Atmosphere, 29 



to arrive at his true meaning, disembarrassed of the somewhat 

 poetical vagueness of his own expressions, and the serious 

 mistakes of his translator; and I believe his view to be this : 

 — There are both transmitted and reflected tints in the sky. 

 The transmitted ones are complementary to the blue of the 

 sky, and therefore, according to Nobili, of the secoyid ordei', 

 whilst all the fiery tints which particularly characterize sunset 

 as contrasted with the dawn, are colours o^xhejirst order re- 

 flected from the vesicular vapours of clouds. 



An ingenious paper by Count Xavier de Maistre on the 

 colour of air and water, appeared in the Bibliotheque Uni^ 

 verselle for November 1832*. With regard to the atmosphere, 

 the author's theory is so far similar to that of Delaval, that its 

 colour is to be iiscribed to the peculiar state of the particles of 

 water contained in it acting on the principle of opalescence, 

 the reflected light being blue and the transmitted orange. 

 He thence refers to the colours of sunset, and adds, — " But 

 it often happens that the colours are not observed, and the sun 

 sets without producing them. It is not, therefore, to the pure 

 air alone that we must attribute the opaline property of the 

 atmosphere, but to the mixture of air and vapour in a parti- 

 cular state, which produces an effect analogous to that of the 

 powder of calcined bones in opaline glass. Neither is it the 

 quantity of water which the air contains that occasions these 

 colours, for when it is very humid, it is more transparent than 

 it is in an opposite state, the distant mountains then appearing 

 more distinct, — a well-known prognostic of rain, and the sun 

 then sets without producing colours; in the fogs and vapours 

 of the morning, the light of the sun is white, but the red 

 colour of the clouds at sunset is generally regarded as the fore- 

 runner of a fine day, because these colours are a proof of the 

 dryness of the air, which then contains nothing more than the 

 particular disseminated vapours to which it owes its opaline 

 property." In this interesting passage we have, I am per- 

 suaded, all that is known of the cause of atmospheric colours, 

 with the single want of the link which shall show that the 

 watery vapour is sometimes capable of absorbing all but red 

 rays, and sometimes notf. 



* Translated in the Edin. New Phil. Journal, vol. xv. 



f Count Maistre explains the colour of the water by similar reasoning. 

 He considers it blue for reflected, and yellowish-orange for transmitted light, 

 and the green colour of the sea and some lakes he attributes to diffused par- 

 ticles which reflect a portion of the transmitted tint, and mingle with the 

 blue. This is well confirmed by Davy's Observations, (Salmonia, 3rd edit. 

 p. 317). Arago has very ingeniously applied the same reasoning to the 

 ocean, showing that when calm it must be blue, but when ruffled, the waves 

 acting the part of prisms, refract to the eye some of the transmitted light 



