558 
MR. W. HUGGINS ON THE SPECTRA 
spectrum of the comet with the diagrams of these spectra of carbon, I was much inter- 
ested to perceive that the positions of the bands in the spectrum, as well as their general 
characters and relative brightness, agreed exactly with the spectrum of carbon when the 
spark is taken in olefiant gas. 
These observations on the spectrum of carbon were undertaken in continuation of my 
researches “On the Spectra of the Chemical Elements”*. I have not presented them 
to the Royal Society, as they are not so complete as I hope to make them. 
Though the essential features of the spectrum of carbon remained unchanged in all 
the experiments, certain modifications were observed when the spectrum was obtained 
under different conditions. One of these modifications, which was referred to in my paper 
“On the Spectra of the Chemical Elements ”f, may be mentioned here. One of the 
strongest of the lines of carbon is a line in the red a little less refrangible than the 
hydrogen line, which corresponds to Fraunhofer’s C. Now this line is not seen when 
the carbon is subjected to the induction-spark in the presence of hydrogen. Two of the 
other modifications of the spectrum of carbon are given in fig. 2. The first spectrum 
represents the appearance of the spectrum of carbon when the induction-spark, with 
Leyden jars intercalated, was taken between the points of wires of platinum sealed in 
glass tubes, and placed almost in contact in olive-oil. In this spectrum are seen the 
principal strong lines which distinguish carbon. The shading of fine lines which accom- 
panies the strong lines cannot be accurately represented on account of the small size of 
the diagram. A spectrum essentially the same is produced when the spark is taken in 
a current of cyanogen. It may be mentioned that when the heating-power of the spark 
was reduced below a certain limit, though the decomposition of the oil still took place, 
the carbon was not volatilized, and the spectrum was continuous. 
The third spectrum in the diagram represents the modification of this typical spectrum 
when the induction-spark is taken in a current of olefiant gas. The highly heated vapour 
of carbon emits light of the same refrangibilities as in the case of the oil ; but the sepa- 
rate strong lines, with a similar power of spark, were no longer to be distinguished. 
The shading, when the carbon was obtained from olefiant gas, was not composed of 
numerous fine lines, but appeared as an unresolved nebulous light. 
Of course in all these experiments the lines of the other elements present were also 
seen, but they were known, and could therefore be disregarded. 
In the^case of the spark in olefiant gas, the three bands in the diagram constitute the 
whole spectrum, with the exception of a faint band in the more refrangible part of the 
spectrum. 
It was with the spectrum of carbon, as thus obtained, that the spectrum of the comet 
appeared to agree. It seemed, therefore, to be of much importance that the spectrum 
of the spark in olefiant gas should be compared directly in the spectroscope with the 
spectrum of the comet. The comparison of the gas with the comet was made the same 
evening, June 23. 
* Philosophical Transactions, 1864, p. 139. + Ibid. p. '145. 
