166 Mr R. Clausius on the 



not be explained by assuming either intense pressure or the 

 original presence of water in the mineral. We have here 

 also a beautiful example of the manner in which water, ope- 

 rating upon inorganic bodies, calls into existence new crys- 

 talline forms ; and we may perceive what a misapprehension 

 it would be of this process, which plays such an important 

 part in the formation of pseudomorphoses, were we to limit 

 it to the originating of kaolins, clays, and other " mineral 

 mires." Moreover, it would seem as if the Elseolite itself 

 were nepheline in process of transformation ; at least this 

 would appear to be indicated by the fluctuating amount of 

 water which the mineral contains. Scheerer has observed of 

 the green and brown Elaeolites of Fredericksvarn, that when 

 these are finely pulverised and decomposed with concentrated 

 muriatic acid, the resulting siliceous earth possesses the same 

 colour, though in a fainter degree, which the mineral pos- 

 sessed before, and that it disappears only on its being dis- 

 solved in nitric acid, or by being brought to a glow ; where- 

 upon he remarks : " This is quite sufficient to prove that the 

 colour is of organic origin." — (Pogg. Ann., v. 49, p. 380.) But 

 how can this organic colouring matter have found its way 

 into the mineral unless by means of water ? Sure enough it 

 was not there originally. — (Poggendorff's Annalen., bd. 87, 

 si 2, 1852, No. 10.) 



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 experiments on the colours of a jet of steam, 

 which connect themselves with the known experiments of 

 Professor Forbes upon the same subject. At the end of his 

 paper Mr Phillips writes — 



" Professor Forbes, after discovering the red colour of a jet 

 of steam, by transmitted light, connected the red colour of the 

 clouds willi this fact ; and the truth of this connection is be- 



