702 
Proceedings of the Roycd Society. 
There are thus 6 conditions under which the spectrum of a per- 
manent elementary gas may be viewed ; but seldom more than two 
or three or these have been observed by any one. 
Thus with Oxygen, the most advanced of all the gases, — 
(1) Its condensed-spark bright-line spectrum has been much 
written on by Angstrom, Thalen, Kirchoff, Bunsen, Hoggins ; and 
the dark reversal of some of these lines is now being worked at by 
Professors Liveing and Dewar. 
(2) Its simple-spark bright-line spectrum is what has been 
described in this paper ; but the dark reversal of these lines, either 
single or triple, has not yet been accomplished by any one. 
(3) Finally its Auroral, or cold-spark spectrum, though never yet 
seen in the bright form, has been long witnessed unconsciously in 
the dark variety by every one who has ever noted the huge telluric 
black lines in the Solar Spectrum known as A, B, and Alpha ; the 
identification of the first two of these lines with Oxygen having 
been recently established by M. Egoroff of St Petersburg, by looking 
through a tube of condensed Oxygen 66 feet long, at a bright con- 
tinuous spectrum of the lime light ; and the structural identity of the 
3rd, with the 1st and 2nd, having been since then most ingeniously 
worked out by M. Cornu in Paris. 
OF HYDROGEN. 
(1) At condensed-spark temperature, and also in the Sun, H’s 
three grand lines are well known, both in the bright and the dark 
conditions. 
(2) Its simple-spark multilinear spectrum, in the bright state, 
has been described here ; but the reversal is unknown. 
(3) And of its cold-spark, or Auroral spectrum, nothing I believe 
is known either in the bright or dark variety. 
AND OF NITROGEN. 
(1) At condensed-spark temperature, the report is the same as 
for Oxygen. 
(2) At simple-spark temperature, the bright line form has been 
described in the preceding pages ; but its reversal is unknown. 
(3) And of its cold-spark, or Auroral spectrum, nothing I believe 
has yet been positively ascertained either for bright or dark lines. 
