508 



Profs. Liveing and Dewar. 



[June 10, 



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

 spectrum produced by changes of temperature. We cannot infer from 

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

 The bands in question are singularly persistent through a great range 

 of temperatures, from the temperature of a cyanogen flame cooled by 

 admixture with carbonic acid gas, as related by Watts ("Phil. Mag.," 

 1869, p. 258), to that of the spark of an induction coil with condenser. 



But 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 that carbon can exist at all in the 

 state of vapour uncombined at the temperature of a cyanogen flame 

 can be adduced, and further independent evidence of the existence of 

 different groupings in such vapour, the hypothesis here enunciated is 

 a gratuitous one, so long as any other hypothesis for which inde- 

 pendent evidence can be adduced, as is true of the existence of nitro- 

 carbon compounds in the flame, arc, and spark, will sufficiently explain 

 the facts. 



Whether or no the nitrocarbon bands are visible in the solar spectrum 

 is not in dispute, for we have never hitherto expressed any opinion on 

 that point. 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, 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 P has far more of the distinctive 

 character of the cyanogen spectrum than any other series in the ultra- 

 violet part of the solar spectrum. 



However that may be, we contend against the hypothesis that if 

 present they can be due to any vapour of carbon uncombined in the 

 upper cooler region of the chromosphere. One object of our investi- 

 gations has been to determine the permanence of compounds of non- 

 metallic elements, and the sensitiveness of the spectroscopic test in 

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

 in the solar atmosphere their presence would be most distinctly re- 

 vealed in the more refrangible part of the spectrum, and this is a 

 subject with which we purpose to deal in a further communication. 

 In the meantime it is sufficiently clear that the presence of nitrogen 

 in the solar atmosphere may be recognised through cyanogen when 

 free nitrogen might escape detection. 



In a footnote of his paper Mr. Lockyer assigns the wave-length 3881 



the least refrangible of those shown in our diagram, fig. 1, then the most persistent 

 in the hydrocarbon flame-spectrum are 2 and 5, while in the visible part of the 

 spectrum of cyanogen they are 3 and 4, but there are conditions of the nitrocarbon 

 spectrum in which the three lines near Gr seem to be most persistent. 



