2 



Profs. G. D. Liveing and J. Dewar. 



circumstances in the spectra of the compounds of carbon. Professors 

 Liveing and Dewar have found for the strong line at the beginning of 

 this group the wave-length 3882*7, and for the second line 38705. 



I am also able to see upon the continuous solar spectrum, a 

 distinct impression of the group of lines between Gr and 7i, which is 

 usually associated with the group described above. My measures for 

 the less refrangible end of this group give a wave-length of 4230, 

 which agrees as well as can be expected with Professors Liveing and 

 Dewar's measure 4220. 



In their paper "On the Spectra of the Compounds of Carbon," 

 " Proc. Roy. Soc," vol. 30, p. 494, Professors Liveing and Dewar 

 show that these two groups indicate the presence of cyanogen, and 

 are not to be seen in the absence of nitrogen. If this be the case, the 

 photograph gives undoubted evidence of the presence of nitrogen in 

 the comet, in addition to the carbon and hydrogen shown to be there 

 by the bright groups in the visible part of the spectrum. On this 

 hypothesis we must further suppose a high temperature in the comet 

 unless the cyanogen is present ready formed. 



I should state that Mr. Lockyer regards the two groups in the pho- 

 tograph, and the groups in the visible spectrum, to be due to the 

 vapour of carbon at different heat-levels ("Proc. Roy. Soc." vol. 30, 

 p. 461). 



It is of importance to mention the strong intensity in the photo- 

 graph of the lines 3883 and 3870, as compared with the continuous 

 spectrum, and the faint bright group beginning at 4230. At this 

 part of the spectrum, therefore, the light emitted by the cometary 

 matter exceeded by many times the reflected solar light. I reserve 

 for the present the theoretical suggestions which arise from the new 

 in formation which the photographs have given us. 



" Note on the Reversal of the Spectrum of Cyanogen." By G. 

 D. Liveing, M.A., F.R.S., Professor of Chemistry, and J. 

 Dewar, M.A., F.R.S., Jacksonian Professor, University of 

 Cambridge. Received July 4, 1881. 



In the course of many observations on the reversal of lines of 

 metallic spectra, we have frequently noticed dark shaded bands which 

 appeared to be the reversals of bands ascribed to the oxides or 

 chlorides of sundry metals ; more particularly we have seen them when 

 experimenting with compounds of the alkaline earths, and we have 

 repeatedly obtained a reversal of the green magnesium-hydrogen 

 series ; but, until recently, we have never seen any reversal of the shaded 

 bands of the spectrum of cyanogen, though our attention has been 



