1882.] On the Spectra of Carbon and its Compounds. 123 



limits. These lines are mapped on the same scale as Angstrom's and 

 Cornu's maps of the solar spectrnm. The paper describes the method 

 of taking the measures, and gives in detail the quantities observed 

 and the data on which the calculations are founded. 



Part II. Received June 15, 1882. 

 (Abstract.) 



In the second part of this paper the authors have gi^en a map of 

 the ultra-violet lines of potassium, sodium, lithium, barium, strontium, 

 calcium, zinc, mercury, gold, thallium, aluminium, lead, tin, antimony, 

 bismuth, and carbon, as developed in the arc. They point out that in 

 several cases the lines are in all probability harmonically related, as 

 shown by the repetition of similar groups of lines at regularly dimi- 

 nishing distances, the groups being alternately sharply denned and 

 diffuse, and becoming more diffuse as they die away at the end of the 

 series. They had previously called attention to this kind of relation- 

 ship between the visible lines in the spectra of the alkalies and of 

 magnesium. The like relationship holds good in the ultra-violet 

 spectra of those metals, and is strongly marked in the cases of calcium 

 and zinc, less strongly in some other metals. 



XII. " General Observations on the Spectra of Carbon and its 

 Compounds." By Professor G. D. Liveing, M.A., F.R.S., 

 and Professor James Dewar, M.A., F.R.S. Received June 

 12, 1882. 



In our two former papers on the spectra of the compounds of 

 carbon with hydrogen and nitrogen (" Proc. Roy. Soc," vol. 30) we 

 described the results of a long series of synthetical and analytical 

 experiments which had enabled us to trace satisfactorily a fluted band 

 spectrum which occurs in the arc and spark discharge in niauy com- 

 pounds of carbon, and generally when carbon poles are used to transmit 

 the current of the arc or spark in air, to the compound substance 

 cyanogen. This led to a further investigation of the carbon ultra- 

 violet line spectrum in order to complete the series of simple vibra- 

 tions which originate from this substance. After all this work a great 

 deal remains to be ascertained regarding the conditions which cause a 

 variation of intensity in the different series of carbon flutings which 

 originate from cyanogen, and also their persistency and development. 



The present paper is a short record of the particular variations in 

 the carbon groups which are revealed in the different photographs of 

 the spectrum of the arc discharge that we have had occasion to take 



