4.">0 C. PIAZZI SMYTH ON MICROMETRICAL MEASURES OF 



PART V. 



Concluding Notes on the Elemental Gases, H, O, and N. 



If in the earlier part of this paper, we found it expedient to admit that the 

 two separate spectra there described were the spectra in each case of a 

 compound Gas, viz.; the one of CH and the other of CO ; and to some degree 

 because the high-temperature or jar discharge gave a totally different spectrum 

 to C alone ; is there not something rather similar to be said touching the 

 spectra we have just been describing for H, O, and N, though they are simple 

 and elementary gases according to the Chemists ? 



There is at least in so far, that if we try said reputed simple gases, not 

 with the weak direct spark which we have been using all along, but with the 

 intensified or jar discharge, there is introduced for each of them a totally 

 different spectrum from that which we have been describing. But why, in 

 that case, are our tube spectra of those gases not ascribed to compounds of 

 each of them with some other, in place of being confined to the one gas alone \ 



Partly, I imagine, because no one knows at present what the other 

 component may be. And partly because there is a very conveniently 

 classifying theory for use in the meantime, which sets forth how one, simple, 

 elemental gas may have two or more different spectra under different 

 temperature circumstances ; granting always that it exists as a gas at those 

 temperatures, and is not, like Carbon, inert and solid at all but one of them. 



M. Thalen has controverted the multiple view for gases in general, not 

 only on the grounds that his deceased, revered, and loved friend M. Angstkom 

 held that each chemical element could have only one spectrum under any, or 

 all, circumstances (though how proved is not stated) — but considers he has 

 demonstrated that the low temperature or " Band-spectrum " of Nitrogen, is 

 the spectrum of the bi-oxide of that gas, and not of that gas by itself. 



In 1872 (Proc. ft. Soc, xx. p. 482) Dr Schuster, the able writer of the 

 Report for the British Association Committee in 1880, held a similar view. 

 But in 1880 he repudiates the idea, and states that no emission, or bright, 

 spectrum has yet been found that can with certainty be referred to a compound 

 of Nitrogen and Oxygen ; so that he restores the "gorgeous Band-spectrum" to 

 Nitrogen alone ; its line spectrum at higher temperature notwithstanding. 



Dr Schuster is also the hero for claiming the particular Oxygen sj)ectrum 

 we have been describing, viz., the spectrum of minute triplets and a few thin 

 lines, for Oxygen alone ; calling it the compound-line, or low-temperature, or 

 simple-spark, spectrum of that gas ; but without invalidating in any degree its 

 claim to the strong Line-spectrum which it shows at high electric temperature. 



