342 



Note on the Spectrum of Carbon. 



[Apr. 29,- 



addition to that or those which give us the line spectrum, and that the 

 tension of the current nsed now brings one set of flutings into promi- 

 nence, and now another. 



I have so often taken occasion to refer with admiration to the work 

 of Angstrom and Thalen that I shall not be misunderstood when I say- 

 that their conclusions, to which such prominence is given, and on 

 which such great stress is laid, by Messrs. Liveing and Dewar, rests 

 more upon a theory which has been shown to be false since the labours 

 commenced and analogy than upon experiment. 



Their work, undertaken at a time when the existence of so-called 

 " double spectra" was not established upon the firm basis that it has 

 now, and when there was no idea that the spectrum recorded for us 

 the results of successive dissociations, gave the benefit of the doubt in 

 favour of flutings being due to compounds, and it was thought less 

 improbable that cyanogen or acetylene should have two spectra than 

 that carbon or hydrogen should possess them. 



These views were accepted by myself until years of work and ex- 

 perience had shown them to be untenable, and later researches have 

 thrown doubt upon the view that the fluted spectra of aluminium and 

 magnesium are entirely 1 due to the oxides of those metals instead of to 

 the metals themselves — and this is the very basis of the analogy which 

 Angstrom and Thalen employed. 



From what I have shown it will be clear that the consequences drawn 

 in the following paragraphs* by Messrs. Liveing and Dewar from the 

 assumed hydrogen-carbon bands are entirely invalid. 



" The similarity in the character of the magnesium-hydrogen 

 spectrum, which we have described, to the green bands of the hydro- 

 carbons is very striking. We have similar bright maxima of light, 

 succeeded by long drawn-out series of fine lines, decreasing in in- 

 tensity towards the more refrangible side. This peculiarity, common 

 to both, impels the belief that it is a consequence of a similarity of 

 constitution in the two cases, and that magnesium forms with hydro- 

 gen a compound analogous to acetylene. In this connexion the very 

 simple relation (2 : 1) between the atomic weights of magnesium and 

 carbon is worthy of note, as well as the power which magnesium has,, 

 in common with carbon as it now appears, of combining directly with 

 nitrogen. We may with some reason expect to find a magnesium- 

 nitrogen spectrum. 



" The interest attaching to the question of the constitution of 

 comets, especially since the discovery by Huggins that the spectra of 

 various comets are all identical with the hydrocarbon spectrum, 

 naturally leads to some speculation in connexion with conclusions to 

 * Paper read February 2, 1880. 



