Auroræ: Their Characters and Spectra. J. Rand Capron
terror.”
Maupertius’s description at Oswer-Zornea.
Maupertius describes a remarkable Aurora he saw at Oswer-Zornea on the 18th December, 1876. An extensive region of the heavens towards the south appeared tinged of so lively a red that the whole constellation of Orion seemed as if dyed in blood. The light was for some time fixed, but soon became movable, and, after having successively assumed all the tints of violet and blue, it formed a dome of which the summit nearly approached the zenith in the south-west.
Red Auroræ rare in Lapland.
Maupertius adds that he observed only two of the red northern lights in Lapland, and that they are of very rare occurrence in that country.
The observations of Carl Bock, the Norwegian naturalist, kindly communicated by him to me, and detailed in Chapter III., quite confirm this observation of Maupertius as to the rare occurrence of red Auroræ in Lapland, he having only seen one.
Plate I.
CHAPTER III.
SOME SPECIFIC DESCRIPTIONS OF AURORÆ, INCLUDING RESULTS OF THE ENGLISH ARCTIC EXPEDITION, 1875–76.
Captain Sabine’s Auroræ.
Captain Sabine’s Auroræ.
Captain Sabine describes Auroræ seen at Melville Island (Parry’s first voyage, January 15). Towards the southern horizon an ordinary Aurora appeared. The luminous arch broke into masses streaming in different directions, always to the east of the zenith.
Curvature of arches towards each other.
The various masses seemed to arrange themselves in two arches, one passing near the zenith and a second midway between the zenith and the horizon, both north and south, but curving towards each other. At one time a part of the arch near the zenith was bent into convolutions like a snake in motion and undulating rapidly.
Aurora seen at Sunderland, February 8th, 1817.
(‘Annals of Philosophy,’ vol. ix. p. 250.)
Aurora seen at Sunderland, Feb. 8, 1817. Formation of corona.
It began about 7 P.M. during a strong gale from the N.W., with single bright streamers in the N. and N.W., which covered a large space and rushed about from place to place with amazing velocity, and had a fine tremulous motion, illuminating the hemisphere as much as the moon does eight or nine days from change. About 11 o’clock part of the streamers appeared as if projected south of the zenith and looked like the pillars of an immense amphitheatre, presenting a most brilliant spectacle and seeming to be in a lower region of the atmosphere, and to descend and ascend in the air for several minutes. (This appears to have been the formation of a corona.) One streamer passed over Orion, but neither increased nor diminished its splendour.
Description of Aurora by Dr. Hayes, 6th January, 1861.
Dr. Hayes’s Aurora, 6th January, 1861.
‘Recent Polar Voyages’ contains a narrative of the voyage of Dr. Hayes, who sailed from Boston on the 6th of July, 1860, and wintered at Port Foulbe. He witnessed a remarkable display of the Aurora Borealis on the morning of the 6th January, 1861.
Development of Aurora.
The darkness was so profound as to be oppressive. Suddenly, from the rear of the black cloud which obscured the horizon, flashed a bright ray. Presently an arch of many colours fixed itself across the sky, and the Aurora gradually developed.
Rays changed to glow.
The space within the arch was filled by the black cloud; but its borders brightened steadily, though the rays discharged from it were exceeding capricious, now glaring like a vast conflagration, now beaming like the glow of a summer morn. More and more intense grew the light, until, from irregular bursts, it matured into an almost uniform sheet of radiance. Towards the end of the display its character changed. Lurid fires flung their awful portents across the sky, before which the stars seemed to recede and grow pale.
Mixed colours. Colours change. Tongues of white flame formed.
The colour of the light was chiefly red; but every tint had its turn, and sometimes two or three were mingled; blue and yellow streamers shot across the terrible glare, or, starting side by side from the wide expanse of the radiant arch, melted into each other, and flung a strange shade of emerald over the illuminated landscape. Again this green subdues and overcomes the red; then azure and orange blend in rapid flight, subtle rays of violet pierce through a broad flash of yellow, and the combined streams issue in innumerable tongues of white flame, which mount towards the zenith.
The illustration which accompanies this description in the work is reproduced on Plate II., and forcibly reminds one of the “curtains” of the Aurora described in the preceding Chapter by Mons. Lottin.
Plate II.
Prof. Lemström’s Aurora of 1st September, 1868.
Prof. Lemström’s Aurora, 1st September, 1868.
In the first Swedish Expedition, 1868, some remarkable observations were made on the appearance of luminous beams around the tops of mountains, which M. Lemström showed by the spectroscope to be of the same nature as Auroræ.
Aurora from earth’s surface. Yellow-green line seen.
On the 1st September, 1868, on the Isle of Amsterdam in the Bay of Sweerenberg, there was a light fall of snow, and the snowflakes were observed falling obliquely. All at once there appeared a luminous phenomenon which, starting from the earth’s surface, shot up vertically, cutting the direction of the falling snowflakes, and this appearance lasted for some seconds. On examination with a spectroscope the yellow-green line was found by Lemström (but of feeble intensity) when the slit of the instrument was directed towards a roof or other object covered with snow, and even in the snow all round the observer.
Lemström’s conclusions.
M. Lemström concluded that an electric discharge of an auroral nature, which could only be detected by means of the spectroscope, was taking place on the surface of the ground all around him, and that, from a distance, it would appear as a faint display of Aurora.
[It should, however, here be noted that the reflection of an Aurora from a white or bright surface would give, in a fainter degree, the spectrum of the Aurora itself; and, apart from the phenomena seen by the eye, the case fails to be conclusive that an Aurora on the surface of the ground was examined.]
Mr. J. R. Capron’s Aurora of October 24th, 1870.
Mr. J. R. Capron’s Aurora, Oct. 24, 1870. Silver glow in north. Phosphorescent cloud-streamers. Crimson masses on horizon. Coloured streamers. Corona formed. Aurora fades away.
The description, from my notes made at the time of this fine display, is as follows:—“Last evening (October 24) the Aurora Borealis was again most beautifully seen here (Guildford). At 6 P.M. indications of the coming display were visible in the shape of a bright silver glow in the north, which contrasted strongly with the opposite dark horizon. For two hours this continued, with the addition from time to time of a crimson glow in the north-east, and of streamers of opaque-white phosphorescent cloud, shaped like horse-tails (very different from the more common transparent auroral diverging streams of light), which floated upwards and across the sky from east and west to the zenith. At about 8 o’clock the display culminated;