Auroræ: Their Characters and Spectra - J. Rand Capron

c. At the aura of the negative pole.

Screw.	Wave-length.	Remarks.
5·18	6100	Broad, moderately bright stripe, indistinct at the edges.
5·70	5945	Broad, moderately bright stripe, indistinct at the edges.
7·60	5159	Broad, moderately bright stripe.
8·41	5289	Broad, moderately bright stripe.
8·76	5224	Very bright line, somewhat indistinct towards the violet.
9·19	5147	Faint line.
10·00	5004	Bright line, indistinct towards the red.
10·67	4912	Somewhat fainter than the last, indistinct towards the red.
11·43	4808	Very faint line.
12·25	4704	Very intense, broad, indistinct towards the violet.
12·73	4646	Very faint line.
13·43	4569	Moderately bright, indistinct towards the violet.
14·25	4486	Like the last.
15·03	4417	Quite a faint line.
15·86	4346	Moderately bright line.
16·76	4275	Very bright line.

Here follow several other lines.

The observations in the different parts of the tube show plainly the dependence of the spectrum on the temperature. The aura of the negative pole gives the line near 10·07 so characteristic of the air-spectrum. This is the same line which is met with in the spectra of most of the nebulæ. The very striking groups of lines in the red and yellow in the spectrum of the narrow part of the tube disappear entirely in the wide part. If we compare the spectra with those above quoted, of oxygen and hydrogen, we find line Hβ very faint in the spectrum of the narrow part of the tube near 11·03; on the other hand, oxygen-lines appear in the broad part near 8·20, 8·94, and 14·07. Thence I would conjecture that the tube was not filled with pure nitrogen, the appearance of which is precise, but with dry rarefied air, since Wüllner’s researches have proved that dry air yields the same spectrum as nitrogen gas. Perhaps the air in the tube examined by me had not been thoroughly dried, and thus the appearance of some lines of the elements before named is to be explained.

I must further mention that the electrodes of the tubes consisted of aluminium; yet a comparison of the spectra observed and the aluminium spectrum has shown no connexion between them.

IV. Atmospheric Air.

Screw.		Wave-length.	Remarks.
	5·88	5892	Very bright double line (Na).
	6·67	5680	Very bright line.
	7·20	5550	Faint line.
	9·00	5180	Very bright line.
	9·79	5047	Fine faint line.
	10·03	5008	Very bright double line.
	10·07	5002	Very bright double line.
	11·43	4803	Faint confused line.
	12·69	4651	Faint line not sharply defined.
	12·84	4633
	13·04	4612
From	14·61	4453	Confused band of light, which ends with a broad washy line.
to	15·88	4444	Confused band of light, which ends with a broad washy line.

Here follow several other lines.