1881.] on the Oi'njin and LlcnlHij of Siiectra, G85 



explanation. IMr. Lockyer, liowcvcr, attempts to explain tlio dls- 

 appoaranco of the bands when nitrogen is absent by the statement, 

 " that tlie tension of the cnrrent nsed now brings one set of flutings 

 into prominence, and now another." This is no new observation. It 

 is well known that variations in the discharge produce variations in 

 the relative intensities of different parts of a spectrum. Certain lines 

 of magnesium, cadmium, zinc, and other metals, very brilliant in the 

 spark, are not seen, or are barely seen, at all in the arc. His remark 

 might be applied to the spectra of compounds as well as to those of 

 elements. Variation in tlie discharge accounts very well for some of 

 the variations of intensity in the bands if they be due to a nitrocarbon ; 

 it will not, however, account for the fact observed by us, that the 

 bands, or those of them which have the greatest emissive power, and 

 are best developed by the particular current used, come out on the 

 addition of a minute quantity of nitrogen, when there is every reason 

 to think that no variation of the current occurs. 



Much the same may be said with regard to the changes of the 

 spectrum produced by changes of tem2)erature. We cannot infer 

 from any of these changes that the spectrum is not due to a 

 compound. 



Again, Mr. Lockyer attempts to get over the difficulties of his case 

 by the supposition that " the sets of carbon flutings represent different 

 molecular groupings of carbon, in addition to that or those which give 

 us the line spectrum." 



Now, until independent evidence can be adduced that carbon can 

 exist in the state of uncombined vapour at the temperature of a 

 cyanogen flame, and that different groupings in such vapour exist, 

 the hypothesis here enunciated is a gratuitous one, so long as the 

 existence of nitrocarbon compounds in the flame, arc, and spark will 

 sufficiently explain the facts. 



The observation above recorded, that there is in the spectrum of 

 cyanogen a strong shaded band coincident with the very characteristic 

 dark shaded band P of the solar spectrum, strengthens materially the 

 evidence in favour of the existence of these bands in the solar 

 spectrum ; the more so, as the series of lines at V has far more of 

 the distinctive character of the cyanogen spectrum than any other 

 series in the ultra-violet part of the solar sjicctrum. 



The hypothesis that if present they are due to vapour of carbon 

 uncombined in the upper cooler region of the chromosphere 

 seems absurd. One object of our investigations has been to 

 determine the permanence of compounds of the non - metallic 

 elements, and the sensitiveness of the spectroscopic test in 

 regard to them. It appeared probable that if such compounds exist 

 in the solar atmosphere their presence would be most distinctly 

 revealed in the more refrangible part of the spectrum. In the mean- 

 time it is sufficiently clear that the presence of nitrogen in the solar 

 atmosphere may be recognised through cyanogen when free nitrogen 

 might escape detection. 



