Auroræ: Their Characters and Spectra - J. Rand Capron

At Tronsa an Aurora was seen October 21st, 1868, which commenced in the north and became very brilliant. The spectroscope showed:—

1. A yellow line at 74·9.

2. A very clear line in the blue at 65·90.

3. Two lines of hair’s breadth, with very pronounced (horizontal?) striæ on the side of the yellow, one at 125 and the other about 105.

[I presume the striæ were really vertical, and that the explanation intended to convey that these lines shaded off towards the yellow. From a comparison of the figures they must have been in the red, and are the only instance recorded of two auroral lines in that region. They are subsequently spoken of as “shaded rays.”—J. R. C.]

MM. Wijkander and Parent’s observations.

M. Auguste Wijkander and Lieut. Parent, of the Swedish Expedition in 1872-73, under Professor Nordenskiöld, used a direct-vision spectroscope, with a micrometer-screw movement of the prisms, the reading being afterwards reduced to wave-lengths upon Ångström’s line-values.

The following Table gives the results, with Dr. Vogel’s lines added for the sake of comparison:—

Lines.	Observations, Wijkander.			Observations, Parent.			Mean of both.	Vogel.
Lines.	Number.	W.L.	Probable error.	Number.	W.L.	Probable error.	Mean of both.	Vogel.
..	..	..	..	..	..	..	..	6297
..	..	..	..	..	..	..	..	5569
(1)	5	5359	±3	..	..	..	5359	5390
(2)	6	5289	±5	3	5280	± 1	5286	..
(3)	6	5239	±4	2	5207	±11	5231	5233
..	..	..	..	..	..	..	..	5189
(4)	5	4996	±9	..	..	..	4996	5004
(5)	1	4871	..	1	4873	..	4872	..
(6)	8	4692	±2	10	4708	± 5	4701	4663
(7)	1	4366	..	..	..	..	4366	..
(8)	4	4280	±3	3	4286	±16	4284	..

The brightest line in all Auroræ, 5567, was intentionally not included in the Tables. The red line was not seen. Nos. 5 and 7 were only seen once, and not in the same Aurora.