SPECTRUM ANALYSIS OF THE HEAVENLY BODIES. 161 
racters, with the spectrum of carbon as it appears when the induction-spark 
is taken in a current of olefiant gas. 
These observations on the spectrum of carbon were undertaken in con- 
tinuance of my researches on the “‘ Spectra of the Chemical Elements.” I 
have not yet made them public, as they are not so complete as I hope to 
make them. 
It may be stated, as the general result of this investigation, that though 
in all cases the essential features of the spectrum of carbon remained unal- 
tered, certain small modifications were observed when the spectrum was 
obtained under different conditions. 
Two of these slightly modified forms of the spectrum of carbon are given 
in fig. 2. Pl. V. The first spectrum was obtained by taking the induction- 
spark between the points of platinum wires, sealed in glass tubes, and im- 
mersed in olive-oil. This spectrum may be taken as exhibiting the typical 
form of the spectrum of carbon. The brilliant line in the red part of the 
spectrum, which is in a small degree less refrangible than the line of hydro- 
gen corresponding to Fraunhofer’s C, is not seen when carbon is heated in 
the presence of hydrogen*, 
The second spectrum in the diagram exhibits the slightly modified spectrum 
which is produced when the induction-spark passes in a current of olefiant 
gasT. It will be seen that the carbon emits light of the same refrangi- 
bility as in the former case; but the separate lines are no longer distinct, 
and the shading is not resolved into the numerous fine lines which were then 
visible. The very close agreement of the comet’s spectrum with this form of 
the spectrum of carbon showed the importance of comparing the two spectra 
directly in the spectroscope. 
On the following evening this was satisfactorily accomplished. My friend 
Dr. W. Allen Miller was present in the observatory on this evening, and kindly 
took part in the observations which were made. 
A glass gas-holder, a (woodcut, p. 162), containing olefiant gas, was con- 
nected by a flexible tube with a glass tube, 4, into which platinum wires were 
soldered. This tube was so fixed that the spark between the wires was suit- 
ably reflected by the small mirror, c, into the spectroscope attached to the 
telescope, so that the spectrum of carbon appeared directly below the spec- 
trum of the comet. 
We were satisfied that within the limits of the dispersive power of the 
instrument employed, which may be taken at about the breadth of the double 
line D, the two spectra were coincident, not only in the position of the bands, 
but also in their general characters, and their relative brightness. 
This direct comparison I repeated on June 25, with an equally satisfactory 
result. ; 
The lines of hydrogen (which, of course, were present in the spectrum of 
the olefiant gas) were not to be seen in the spectrum of the comet. 
The very close resemblance of the spectrum of this comet to the spectrum 
of carbon necessarily suggests the identity of the substances by which, in 
both cases, the light was emitted, though indeed the great fixity of carbon 
seems to raise a difficulty in the way of accepting this conclusion. Some 
two or three comets have been known to approach the sun sufficiently near 
to acquire a temperature high enough to convert even carbon into vapour. 
Indeed for such comets a body of some fixity seems to be necessary. With 
* Phil. Trans. 1864, p. 145. 
+ In the Plate the bright line at the beginning of the middle band of this spectrum is 
made too strong. 
1868. N 
