SUPPLEMENTARY REPORT ON METEOROLOGY. 121 
them do, of the general glow so common at sunset which is 
communicated to all objects indifferently, and which ceases 
when the sun leaves them in the shade; and (3) that the colours 
of clouds analysed by a prism by Sir D. Brewster* do not 
appear to be composed as the colours of thin plates are. 
251. Mariotte asserted} that the proper colour of air is 
blue, just as he considers that of water to be green, and as 
other bodies have peculiar tints. Bouguer revived this doc- 
trinet, and added to it the consideration, that if air reflect 
blue light it may be expected to transmit the complementary 
colour as red (as is stated to be the case with sea-water), and 
hence he explained the fiery colour of the horizontal sun, and 
the tints of sunset. This opinion has been adopted by Euler§, 
Leslie ||, and many later writers, but especially by Brandes, 
who, in a most ingenious article in Gehler’s Dictionary], has 
maintained its complete adequacy to the explanation of phe- 
nomena. 
252. This theory must, I think, be considered imperfect 
rather than erroneous. That the colour of pure air by reflexion is 
blue, can, I think, hardly be doubted. But that the explanation 
of the hues of sunset is incomplete, can be doubted by no one 
who is unable to persuade himself, with Brandes, that the dif- 
ference of intensity on different evenings is only an ocular 
deception, or depends on the presence of clouds which receive 
and repeat the colour. 
253. Something more is wanting, then, to the explanation, 
and many acute writers have supposed that some impurity in 
the air produces, by its absorptive action and variable quantity, 
the phenomena in question; and several of these authors com- 
pare the effect to that of opalescence in turbid fluids, which 
generally transmit a ruddy beam. Under this head we class 
Honoratus Fabri**, our countryman Thomas Melvilltt, De- 
laval{t, Count Maistre§§, and Sir D. Brewster||||. Of these 
writers, Count Maistre is the only one who suggests that 
watery vapour, under peculiar mechanical conditions, may be 
the source of the variable atmospheric hues, ‘‘ producing an 
* Edinburgh Transactions, xii. 544. Compare Encyclopedia Britannica, 
art. Optics, p. 510. 
+ Cuvres, i. 299. Leide, 1717. t Traité d’ Optique, p. 365—8. 
§ Letters, ii. 507. || Encyclopedia Britannica, art. Meteorology. 
4 Art. Abendréthe, vol.i. p. 4. 
** Quoted by Eberhard. Rozier, i. 620. 
++ Edinburgh Physical and Literary Essays, p. 81. 
tt Manchester Memoirs, First Series, ii. 214. 
§§ Bibliotheque Universelle, November, 1832. 
\\|| Edinburgh Transactions, xii. 580. 
