I have subsequently, in another section of this Chapter, added a full catalogue of the Auroral lines, prepared by myself from the foregoing and other sources and observations; and I also append to it a Plate [Plate XII.], in which these lines are positioned and the wave-lengths and names of observers are given. The numbers of the lines on the Plate correspond with those in the catalogue. The solar spectrum and the spectrum of the blue base of a candle-flame are added for purposes of comparison. [The telluric bands in the solar spectrum are shown more distinctly than they actually appear, and do not profess to give details.] _Flickering of the Green Line._ [Sidenote: Flickering of the green line. Herschel’s observation. J. R. Capron’s observation.] A. S. Herschel noticed this, April 9th (1871?). He says:—“A remarkable circumstance connected with the appearance of the single line observed on this occasion was the flickering and frequent changes with which it rose and fell in brightness; apparently even more rapidly than the swiftly travelling waves, or pulsations of light, that repeatedly passed over the streamers, near the northern horizon, towards which the spectroscope was directed.” In the spectrum of the Aurora of 20th October, 1870, I saw and noted the green line as “considerably flickering;” and in the Aurora of 4th February, 1872, I again saw and noted “the peculiar flickering” I had remarked in 1870. I have not seen the peculiarity noted by other observers. _Mr. Backhouse’s graphical Spectra of four Auroræ._ [Sidenote: Mr. Backhouse’s graphical spectra of Auroræ.] Mr. Backhouse has been good enough to supply me with some details of four several Auroræ seen by him at Sunderland, accompanied by drawings, showing in a graphical way the spectrum of each display as seen with a spectroscope with rather a wide slit and as drawn by eye. I have reduced the four drawings to the same scale, and in this way they are extremely interesting for comparison (Plate V. fig. 4). The line on the left in each spectrum is Ångström’s bright Auroral line, and is supposed to be considerably prolonged. The height of the lines denotes intensity. [Sidenote: April 18, 1873.] April 18th, 1873, was a bright Aurora. No. 3 is a faint band, which Mr. Backhouse had not perceived before. No. 5 had not been visible lately, and Mr. Backhouse thought it must belong to Auroræ of a different type from those which had appeared latterly. [Sidenote: Feb. 4, 1874.] February 4th, 1874. In the spectrum of this Aurora Mr. Backhouse saw seven lines, all that he had ever seen. (The red line, not shown in the diagram, makes the seventh.) The spectrum is represented as seen between 6.50 and 7.5 P.M. Mr. Backhouse had only once before seen No. 4, and it became quite invisible between 7.45 and 7.55, though the other lines were as bright as before and the red line had appeared. [Sidenote: Oct. 3, 1874.]