Colours of a Jet of Steam. 167 



yond dispute. So far, however, as I have been able to go, 

 the colours of the steam-jet are manifestly only influences of 

 ordinary interference, greatly resembling that produced by 

 thin transparent plates. Thus in (192) the transmitted light 

 is red, as in Professor Forbes's experiments, but the re- 

 flected light is blue. It is therefore to be inferred, that all 

 the colours of the clouds originate in interference, caused by 

 minute drops of water, the size of which determines their 

 colour ; while the blue jet (192) is, I think, strictly analogous 

 to the blue sky." 



With reference to this passage I permit myself to make 

 the following remarks : — The blue colour of the firmament 

 and the morning and evening red were explained by me in 

 1849* upon the principles of " ordinary interference ;" and 

 some time afterwardsf I applied the same explanation to the 

 colours of a jet of steam observed by Professor Forbes. 



In one point, however, my view diverges from that of Mr 

 Reuben Phillips. He names the water-particles which cause 

 the interference " drops of water," while I believe that they 

 are water- bladders, for which view I have adduced my rea- 

 sons in a separate paper.J 



Besides this, I should like to mention two points, with re- 

 gard to which I have been unable to obtain from the paper 

 of Mr Phillips a clear notion of the author's opinion. 



(1.) Among the various colours of the atmosphere there 

 appears to me to exist only two simple originating ones ; 

 namely, the blue colour in all its shades, from dark blue to 

 white, due to interference by reflection; and orange-red 

 colour in the corresponding shades, due to interference by 

 transmission. The other colours exhibited at times in va- 

 rious portions of the heavens, as, for example, purple or green, 

 I hold to be due to the mixing of the above two colours in 

 their different shades. 



* Poggendorff's Annalen, vol. lxxvi., p. 188. 



t Die Licht Erscheinungen der Atmosphare, described and explained by R. 

 Clausius. Leipzig, E. B. Schwickert, 1850. Also under the title Beitrage zur 

 Meteorologische Optik, published by John Aug. Grunert. Part 1, No. 4, p. 395, 

 and in Pogg. Ann., vol. Ixxxiv., p. 449. 



| Pogg. Ann., vol. lxxvi., p. 161. 



