No principal line, and one subsidiary line only, actually coincide with the Aurora-spectrum, this last being that to which Dr. Vogel assigns an identical wave-length, viz. 5189. Other of the subsidiary lines, however, fall somewhat near the Aurora-lines 5569, 5390, 5233, and 5004, two faint lines also falling within the band 4694 to 4629. [Sidenote: Comparison of the lines.] The lines (adopting Dr. Vogel’s wave-lengths for the H lines) were, when compared, as under:— {4694} Aurora 5569 5390 5233 5189 5004 { to } band. {4629} Hydrogen 5555 5422 ... 5189 5008 4632 I remarked that a line (5596) described by Dr. Vogel as “very bright” in his H spectrum does not appear in my tube, though in most other respects our H spectra agree. [Sidenote: Effect of distance on the spectrum.] I thought this tube afforded a good opportunity for testing the effect of distance upon the spectrum. The slit was made rather fine. At 6 inches distance from it the line α in the blue-green (F solar) was very bright. The lines marked β, γ, δ, ε, and ζ also survived, but were faint. At 12 inches from the slit α and γ were alone seen, and at 24 inches α stood by itself upon a dark ground. I also noticed that the red and yellow parts of the spectrum first lost their light on the tube being withdrawn from the slit; and this appeared to account for β disappearing while γ survived. For drawing of the hydrogen-tube spectrum see Plate XIV. spectrum 1. The question of effect of distance upon the spectroscopic appearance of a glowing light, as tested for this and other tubes, seems an important one. It may possibly account for the generally faint aspect of the lines in the more refrangible part of the Auroral spectrum. [Illustration: Plate XIV.] _Carbon- and Oxygen-tubes._ [Sidenote: Carbon- and oxygen-tubes. Tubes described. Carbon-tubes lighted up. Spectra of the carbon-tubes described.]