and of the Analysis of the Solar Atmosphere. 255 



out under the most simple conditions — such, for instance, as the 

 examination of the spectra of flames. Observations of this kind 

 were made in the year 1845 by Professor W. Allen Miller, but 

 they do not furnish any contribution towards a solution of the 

 question. Dr. Miller has the merit of having first published 

 diagrams of the spectra of flames*; but these diagrams are but 

 slightly successful, although in a republication in the ' Che- 

 mical News' t of the paper accompanying these drawings, Mr. 

 Crookes remarks — "We cannot, of course, give the coloured 

 diagrams with which it was orignally illustrated ; but we can 

 assure our readers that, after making allowance for the im- 

 perfect state of chromolithography sixteen years ago J, the dia- 

 grams of the spectra given by Prof. Miller are more accurate 

 in several respects than the coloured spectra figured in recent 

 numbers of the scientific periodicals." In reply to this " as- 

 surance " of Mr. Crookes I only have to remark that, by way of 

 experiment, I have laid Prof. Miller's diagrams before several 

 persons conversant with the special spectra, requesting them to 

 point out the drawing intended to represent the spectrum of 

 strontium, barium, and calcium respectively, and that in no 

 instance have the right ones been selected. 



Swan was the first who endeavoured experimentally to prove 

 whether the almost invariably occurring yellow line may be 

 solely caused by the presence of sodium- compounds. In his 

 classical research " On the Spectra of the Plames of the Hydro- 

 carbons "§ (referred to both in my ' Researches ' and in the 

 paper published by Bunsen and myself), Swan shows how small 

 the quantity of sodium is which produces this line distinctly ; he 

 finds that this quantity is minute beyond conception, and he con- 

 cludes — "When indeed we consider the almost universal diffusion 

 of the salts of sodium, and the remarkable energy with which they 

 produce yellow light, it seems highly probable that the yellow line 

 R, which appears in the spectra of almost all flames, is in every 

 case due to the presence of minute quantities of sodium." 



The strict subject-matter of Swan's investigation was the 

 comparison of the spectra of flames of various hydrocarbons. 

 " The result of this comparison has been, that in all the 

 spectra produced by substances, either of the form C r H s , or of 

 the form C r H s 0*, the bright lines have been identical. In 

 some cases, indeed, certain of the very faint lines which occur 

 in the spectrum of the Bunsen lamp were not seen. The bright- 



[* Phil. Mag. for August, 1845.] 

 t Chemical News, May 18, 1861. 



[J Prof. Miller's diagrams are not printed by chromolithography, but, as 

 is seen on inspection, tinted by hand. — H. E. R.] 

 § Trans. Roy. Soc. of Edinburgh, vol. xxi. p. 414. 



