and of the Analysis of the Solar Atmosphere. 261 



Analysis," reprinted in the ' Chemical News ' of April 19, 1862, 

 Prof. Miller quotes these words without making any remark 

 upon the relation in which his observations, and the conclusion 

 which he draws from them, stand to what I have discovered. 

 In the Number of the same Journal for May 18, 1862, Mr. 

 Crookes writes with reference to these same words, " This para- 

 graph shows that Prof. Miller has anticipated by nearly sixteen 

 years, the remarkable discovery, ascribed to KirchhofF, of the 

 opacity of certain coloured flames to light of their own colour." 

 We need only to read Miller's words with some slight attention 

 to perceive, not only that the conclusion to which he arrives is 

 exactly the opposite of mine, but likewise that his conclusion is 

 incorrect. If weak daylight be allowed to pass through a co- 

 loured flame, the absorption of the latter is not noticeable ; its 

 bright lines appear brighter than the surrounding parts, because 

 in them the light of the flame is present in addition to the day- 

 light. 



5. Soon after my first short publication* concerning the che- 

 mical analysis of the solar atmosphere, I received the following 

 communication in a letter from Prof. Wm. Thomson : — "Professor 

 Stokes mentioned to me at Cambridge some time, probably 

 about ten years, ago, that Professor Miller f had made an 

 experiment testing to a very high degree of accuracy the agree- 

 ment of the double dark line D of the solar spectrum with the 

 double bright line constituting the spectrum of the spirit-lamp 

 burning with salt. I remarked that there must be some physical 

 connexion between, two agencies presenting so marked a charac- 

 teristic in common. He assented, and said he believed a me- 

 chanical explanation of the cause was to be had on some such 

 principles as the following : — Vapour of sodium must possess 

 by its molecular structure a tendency to vibrate in the periods 

 corresponding to the degree of refrangibility of the double line 

 D. Hence the presence of sodium in a source of light must 

 tend to originate light of that quality. On the other hand, 

 vapour of sodium in an atmosphere round a source, must have a 

 great tendency to retain in itself, t. e. to absorb and have its 

 temperature raised by light from the source of the precise 

 quality in question. In the atmosphere around the sun, there- 

 fore, there must be present vapour of sodium, which, according 

 to the mechanical explanation thus suggested, being particularly 

 opake for light of that quality, prevents such of it as is emitted 

 from the sun from penetrating to any considerable distance 

 through the surrounding atmosphere. The test of this theory 

 must be had in ascertaining whether or not vapour of sodium has 



* Monatsberichte der K. Acad, der Wissensch. 8vo. Berlin, Oct. 1859. 

 t [Professor W. H. Miller of Cambridge.— H. £. R.] 



