196 Proceedings of the Itoyal Society of Edinburgh. 



the atmosphere, lead the author to suggest this singular property 

 of condeusing vapour as the probable cause of those phenomena, of 

 which no satisfactory explanation could be given wliilst this fact 

 remained unknown. The prognostics of weather derived from the 

 colours of the sky also receive elucidation from the fact. 



Judging from the similarity of colour of steam and that of nitrous 

 acid gas, and the remarkable power of absorbing certain definite 

 rays of the spectrum discovered in that gas by Sir David Brewster, 

 the author thought it probable that similar lines might be discover- 

 ed in the spectrum formed by light transmitted through steam, 

 and that these might be found to coincide with the atmospheric 

 lines of the spectrum noticed by the same pliilosopher. The ex- 

 periment was made with great care, but the expected result has 

 not been hitherto obtained. The general action of steam on the 

 spectrum is to absorb the violet, blue, and yellow rays, finally 

 leaving only the red and orange, with an imperfect green. 



Since a portion of watery vapour in a confined space, originally 

 transparent and colourless, may become, by mere change of tem- 

 perature, first deep orange-red and transparent, and finally white 

 and semiopake, the author notices another analogy with the singu- 

 lar eflPect of temperature in deepening the colour of nitrous acid 

 gas, and thinks that these facts may one day throw some farther 

 light on the difficult subject of the mechanical constitution of va- 

 pours, and particularly of clouds. 



2. On the meaning of the Homeric terms ^£^;<r, 6/xj), rifiri, iroivn, 

 with their more important compounds and derivatives. 

 By the Venerable Archdeacon Williams. 



February 4. — Dr Aberchombii!;, V. P., in the Chair. The 

 following communication was read : — 



The Colours of the Atmosphere considered with reference 

 to a paper " On the Colour of Steam under certain cir- 

 cumstances," read at the last meeting of the Royal Society. 

 By Professor Forbes. 



The object of this paper was to develope an application of the 

 fact communicated by the author on the 21st January. It was 

 then remarked, that the discovery that steam in a certain stage of 

 condensation is deeply red-coloured for transmitted light, seemed 

 to offer a probable solution of a difficulty which has never yet been 

 fairly met, namely, the red colour of clouds at sunset, and the red- 

 ness of light transmitted throvigh certain kinds of fogs. 



A pretty full history of theories proposed to account for the co- 

 lours of the atmosphere was first given ; it was obtained in almost 

 every case from an examination of the original authorities. These 

 theories were reduced under three general heads, exclusively of 

 that of Gothe, and of most writers before Newton, that the blue 



