404 Profs. Gr. D. Liveing and J. Dewar. [Mar. 9, 



shown the importance of a thorough, and accurate knowledge of the 

 ulfcra-violet spectra of the elements, for it is in the lines of short 

 wave-length as a rule that the greatest emissive power is manifested, 

 and they are therefore most readily reversed. Thus we have suc- 

 ceeded in reversing upwards of 100 lines in the ultra-violet spectrum 

 of iron ("Proc. Roy. Soc," vol. 32, p. 404). The necessity for 

 accurate data in regard to this region of the spectrum led us to make 

 a long study of the spectrum of magnesium, and the results of this 

 investigation appeared in the volume of the " Proc. Roy. Soc." just 

 cited. Having had occasion to examine the origin of the different 

 fluted spectra of carbon, it became apparent that a complete knowledge 

 of the relations of these spectra to the simple spectrum of the element 

 could only be reached by the help of a complete record of the line 

 spectrum. Angstrom and Thalen, in their memoir " On the Spectra 

 of the Metalloids " (Nova Acta Reg. Soc. Upsal., Ser. iii, vol. ix), give 

 a map and table of wave-lengths of the lines due to carbon in the 

 visible part of the spectrum, as distinguished from the fluted spectra 

 given by compounds of carbon, namely, carbonic oxide, cyanogen, and 

 acetylene. These lines, they state, always appeared when very power- 

 ful induction sparks were passed through the vapour of any compound 

 of carbon, or between carbon electrodes. This line spectrum is 

 remarkable for simplicity, consisting of eleven lines, of which the 

 single line in the yellow, followed by a triple group in the green, and 

 a very strong line in the blue, recall vividly the spectrum of magne- 

 sium ; and as we know two modifications of the spectrum of magne- 

 sium which seem to be due respectively to the oxide and a hydride, 

 the parallel between the behaviour of the two elements is the more 

 striking. The plates of the ultra-violet spectra of the metals by the 

 late Professor W. A. Miller ("Phil. Trans.," 1864) include plates of 

 the spark taken between metallic electrodes in different compounds of 

 carbon, which show with sufficient clearness that there are some five 

 groups of lines in the ultra-violet spectrum of this element. In the 

 observations here described we have preferred taking intense induc- 

 tion sparks between pure graphite poles in different gases. 



The accompanying figure represents the ultra-violet spectrum of 

 carbon to a scale of wave-lengths within the range of the rays trans- 

 mitted through calcite. The lines figured have been observed in 

 photographs of the spark of a large induction coil, having a large 

 Leyden jar in connexion with the secondary coil, between poles of 

 purified graphite in air, carbonic acid gas, hydrogen, and coal-gas. 

 The same lines have been observed in photographs of the spark 

 between iron, and between aluminium poles in carbonic acid gas. By 

 comparing the photographs taken under these different circumstances, 

 we have, we believe, eliminated the air lines, which are numerous and 

 strong in the region between H and T, and will form the subject of a 



