26 Professor Forbes on the Colours of the Atmosphere. 



the exposed eye) on the blue which it sees, and being its com- 

 plementary colour, or nearly so, it must tend to diminish the 

 blueness, and finally to produce white. 



Berzelius adopts the view which considers the air itself 

 coloured*. 



In the older writings of Sir David Brewster, we find the 

 theory of Bouguer maintained j- ; but since he has been led to 

 what we must consider, for a majority of cases, a refutation 

 of the Newtonian doctrine of the colours of bodies, he was 

 naturally induced to view with doubt the composition of the 

 celestial blue, and especially of the colours of clouds. That 

 the reflected and transmitted tints should be complementary, 

 as Newton's theory assigns, is well known to be rather the 

 exception than rule in coloured bodies generally ; and a very 

 simple prismatic analysis, which it seems difficult to miscon- 

 strue, proves that the composition of colours — the green of 

 leaves, for instance, — is widely different from that which the 

 doctrine of thin plates would infer J. " I have analysed too," he 

 says, "the blue light of the sky, to which the Newtonian theory 

 has been thought peculiarly applicable, but, instead of finding 

 it a blue of ihe first order, in which the extreme red and ex- 

 treme violet rays are deficient, while the rest of the spectrum 

 was untouched, I found that it was defective in rays adjacent to 

 some of the fixed lines of Fraunhofer, and that the absorptive 

 action of our atmosphere widened, as it were, these lines. 

 Hence, it is obvious, that there are elements in our atmosphere 

 which exercise a specific action upon rays of definite refrangi- 



bility I have obtained," he adds, "analogous results 



in analysing the T/fZ/otu, orange^ red, and purple light which is 

 reflected from the clouds at sunset §." Such a prismatic ana- 

 lysis as is here referred to, is even more satisfactory than in the 

 case of the juices of plants, because here the very reflected light 

 itself is examined in the state it reaches the eye. I need hardly 

 add, that this experiment is not less conclusive against the 

 subjective theory of Muncke, than against the theory of thiii 

 plates of water of Newton and his followers. 



Forster, in his treatise on Atmospheric Phoenomena, main- 

 tains the doctrines of Melvill respecting the colour of clouds. 

 "We observe," he says, "that clouds of the same variety, 

 having the same local or angular position with respect to the 



• Lehrbuch dc-r Chcmie, Wcihler's edit. ] 825, i. 346. 



f Eclin. Encyclopaedia, art. Ojillcs, p. 620. Compare articles Atmosphere 

 and Cyanometer. 



t Life of Newton, p. 78. 1831. Ed. Trans, xii. 538. 



<^ Ed. Trans, xii. 544. Compare Encyc. Brit, new Edition, art. Optics, 

 p. 610. 



