416 On the Colours of a Jet of Steam and of the Atmosphere. 



which weakens the bhie, are said when combined to convert the 

 blue into violet. The explanation is the same as for olive oil. 



Red, reflected from a plate of brass, becomes orange according 

 to Sir John Herschel. The means of explaining this is given 

 by Airy in his memoir against Brewster. 



I have now mentioned all the facts adduced by Brewster. 

 Although I have been unable to repeat all his experiments, 

 I believe the discussion of those which I have succeeded in 

 repeating, abundantly proves that in his method many hitherto 

 unobserved influences come into play, which render a sure judge- 

 ment of the colours impossible and deprive his arguments of all 

 force. If the assumed connexion of the refrangibility or length of 

 wave with colour is to be proved erroneous, it must be done by 

 some more certain method of observation, similar, for example, 

 to that which I have described in this memoir ; a principal con- 

 dition of which is, that the colour investigated be separated from 

 the other colours and rendered free from every trace of irregu- 

 larly dispersed light. 



LXIV. On the Colours of a Jet of Steam and of the Atmosphere. 

 By R. Clausius. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN the August Number of the Philosophical Magazine (p. 128) 

 Mr. Reuben Phillips describes a series of interesting expe- 

 riments on the colours of a jet of steam, which connect them- 

 selves with the known experiments of Prof. Forbes upon the same 

 subject. At the end of his paper Mr. Phillips writes, — • 



" Prof. Forbes, after discovering the red colour of a jet of 

 steam by transmitted light, connected the red colour of the 

 clouds with this fact ; and the truth of this connexion is beyond 

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

 of the steam-jet are manifestly only influences of ordinary inter- 

 ference, greatly resembling that produced by thin transparent 

 plates. Thus in (192) the transmitted light is red, as in Prof. 

 Forbes's experiments, but the reflected light is blue. It is 

 therefore to be inferred, that all the colours of the clouds origi- 

 nate 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 Armament and the 

 morning and evening red were explained by me in 1849* upon 



* Poggendortf' s Annalen, vol. Ixxvi. p. 188. 



