+-----+---------+--------+-------+-------------------+--------+ |Line.| Reading | Wave- |Assumed| Comments. |Probable| | |on scale.|lengths.| line. | | error. | |-----+---------+--------+-------+-------------------+--------| | 1. | 61 | 5690 | 5570 |Common Aurora-line.| -20 | | 2. | 68 | 5320 | 5316 | Corona line. | + 1 | | 3. | 80 | 4850 | 4860 | F, hydrogen. | - 3 | | 4. | 98 | 4350 | 4340 | G, hydrogen. | + 6 | +-----+---------+--------+-------+-------------------+--------+ [61 is evidently wrong, and was probably a mistake for 63.] [Sidenote: G. F. Barker’s observations.] George F. Barker, observing at New Haven (U.S.A.), saw, on November 9th, a crimson and white Aurora, which he examined with a single glass-prism spectroscope, by Duboscq, of Paris. The line positions were obtained by an illuminated millimetre scale. In the white Aurora were four lines (the red one being absent); in the red Aurora five. The wave-lengths of the Aurora-lines were run out as follows:— (1.) Between C and D, 6230 (Zöllner’s 6270). (2.) ” D and E, 5620 (Ångström’s 5570). (3.) ” E and _b_, 5170 (Winlock’s 5200). (4.) ” _b_ and F, 5020. (5.) ” F and G, 4820 (Alvan Clarke’s, jun., 4850). [Sidenote: Spectrum of Aurora of Feb. 4, 1872. Prof. Piazzi Smyth’s observations.] Mr. Procter’s Aurora-lines will be found noticed in connexion with the spectrum of oxygen; and Lord Lindsay’s lines, with a comparison scale drawing, are separately described further on in this Chapter. The Aurora of February 4th, 1872, had many observers; some of whom communicated at the time spectroscopic notes. Professor Piazzi Smyth minutely describes the display as seen in Edinburgh, and saw “Ångström’s green Aurora-line perpetually over citron acetylene[13] at W.L. 5579, and the red Aurora-line between lithium _a_ and sodium _a_, but nearer to the latter, say at W.L. 6370.” Extremely faint greenish and bluish lines also appeared at W.L. 5300, 5100, and 4900 nearly. [Sidenote: Rev. T. W. Webb’s observations.] The Rev. T. W. Webb, with a very fine slit, saw the green Auroral line even in the light reflected from white paper. With a wider slit he saw a crimson band in the brighter patches of that hue, and beyond an extent of greenish or bluish light, which he suspected to be composed of contiguous bands. [Sidenote: R. J. Friswell’s observations.] R. J. Friswell, coming up the Channel at 9.40, with a Hoffman’s direct-vision spectroscope (the observing telescope removed), saw the green line, a crimson line near C, and faint traces of structure in the blue and violet. [Sidenote: The Rev. S. J. Perry’s observations.]