1881.] Note on the Reversal of the Spectrum of Cyanogen. 



< > 



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 

 information which the photographs have given us. 



The diagram shows the two sets of bright lines and the solar spec- 

 trum. There is also indicated in it a small increase of brightness 

 between h and H, which was suspected in the photograph. 



[The accompanying lithograph was executed by order of the British 

 Association for the Advancement of Science, for the illustration of the 

 forthcoming Report for 1881. The use of the stone has been allowed 

 to the Royal Society by the Council of the Association. — Gr. G. 

 Stokes, Sec. U.S.] 



II. " 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 

 constantly directed to this spectrum. Quite lately, however, we have 

 obtained photographs which show the reversal of the violet and 

 ultra-violet bands of this spectrum ; and the fact is perhaps of suffi- 

 cient interest, especially in connexion with the question of the occur- 



B 2 



