Auroræ: Their Characters and Spectra. J. Rand Capron
a shower of rain fell. The corona was remarked upon as unusual. At Edinburgh the sky was brilliant for several hours. (The date of this Aurora is uncertain, as the account is from an undated newspaper cutting. It is supposed to be in February 1872, but could hardly have been on the 4th, as the Aurora of that date did not reach its maximum development at Edinburgh till 8 P.M.)
Mr. J. R. Capron’s Aurora, seen at Guildown, Guildford, February 4th, 1874.
Silvery brightness in N.E. Light-cloud, which moved from E. to W. Formation of arc in N. Streamers. Horizontal clouds of misty light.
About 7 P.M. my attention was drawn to a silvery brightness in the north-east. Above, and still more to the east, was a bright cloud of light, which looked dense and misty, and gave one the impression of an illuminated fog-cloud. The edges were so bright that the adjacent sky, but for the stars shining in it, might, by contrast, have been taken for a dark storm-cloud. The light-cloud expanded upwards until its apex became conical, and then moved rapidly from east, along the northern horizon, until it reached the due west, where it rested, and formed for some time a luminous spot in the sky. About the same time a long low arch of light formed along the northern horizon, having a brighter patch at each extremity; and these being higher in the sky, the arch and turned-up ends were in shape like a Tartar bow. This bow was permanent; and later on a cloud of rose-coloured light formed in the east, looking like the reflection of a distant fire. From the bow also shot up curved streamers of silver light towards the zenith, which at one time threatened to form a corona. This, however, did not happen, and the Aurora gradually faded away, until, when the moon rose about 8, a silver tinge in the east alone remained. I should also mention that fleecy horizontal clouds of misty light floated in the north above the bow across the streamers.
Mr. H. Taylor informed me he saw a similar Aurora some three weeks before, in which the bright horizontal light and short white streamers were the main characters. I am not sure that the horizontal light-clouds were not actual mist-clouds illuminated by reflection of the Aurora; not so, however, I think, the first-mentioned cloud, which had more the appearance of the aura in the large end of an illuminated Geissler tube.
Spectrum of the Aurora described.
I examined the Aurora with a Browning direct-vision spectroscope, and found Ångström’s line quite bright, and by the side of it three faint and misty bands towards the blue end of the spectrum upon a faintly illuminated ground. I could also see at times a bright line beyond the bands towards the violet. There was not light enough to take any measurements of position of the lines.
I made a pencil sketch of this Aurora, at the time when the light-cloud had moved W. and the arc formed, and of the spectrum. These drawings are reproduced on Plate VI. figs. 1 and 1a.
Plate VI.
Mr. Herbert Ingall’s Aurora, July 18th, 1874.
Mr. Herbert Ingall’s Aurora, July 18, 1874. Haze canopy formed. Bright bluish flames appeared. Beams and streamers appeared. Oscillatory motion of rays.
An Aurora of July 18th, 1874, seen by Mr. Herbert Ingall at Champion Hill, S.E., was described by him as an extraordinary one. About 11 the sky was clear; at midnight the sky was covered by a sort of haze canopy, sometimes quite obscuring the stars, and then suddenly fading away. Mr. Ingall was shortly after remarking the sky in the S.E. and S. horizon as being more luminous than usual, when his attention was drawn to a growing brightness in the S.W., and a moment afterwards bright bluish flames “swept over the S.W. and W. horizon, as if before a high wind. They were not streamers, but bright blue flames.” They lasted about a minute and faded; but about two minutes afterwards a glowing luminosity appeared in the W.S.W., and broke into brilliant beams and streamers. The extreme rays made an angle of 90° with each other, the central ray reaching an altitude of 50°. The extreme divergence of the streamers (indicating their height above the earth’s surface), and their direction (from W.S.W. to E.N.E.) at right angles to the magnetic meridian, suggested to Mr. Ingall a disturbance of an abnormal character. The rays had an oscillatory motion for about fifteen seconds, and then disappeared, “as if a shutter had suddenly obscured the source of light.”
Mr. Ingall’s remarks corroborated.
Mr. Ingall’s remarks were corroborated by an observer in lat. 54° 46´ 6″·2 N., long. 6h 12m 19s·75 W. The display, however, was more brilliant, and the intensity of light at midnight illuminated the whole district as with an electric light. The rays, too, bore tints differing from one another; the largest seemed to partake of the nature of the blue sky, while the smaller ones, running parallel with the horizon, were ever changing from blue to orange-red.
Rev. C. Gape saw flashes or streaks of a pale blue colour.
On June 25 (same year?), between 9 and 10 o’clock, the Rev. Chas. Gape saw at Rushall Vicarage, Scole, Norfolk, in the E.S.E., very frequent flashes or streaks of a pale blue colour darting from the earth towards the heavens like an Aurora. The day had been dull and close, with distant thunder. In the E.S.E. it was dark, but overhead and everywhere else it was clear and starry.
Mr. J. R. Capron’s White Aurora of September 11th, 1874.
Mr. J. R. Capron’s white Aurora of Sept. 11, 1874.
On September 11, 1874, we were at Kyle Akin, in the Isle of Skye. The day had been wet and stormy, but towards evening the wind fell and the sky became clear. About 10 P.M. my attention was called to a beautiful Auroral display.
Double arc of pure white light in the N.
No crimson or rose tint was to be seen, but a long low-lying arc of the purest white light was formed in the north, and continued to shine with more or less brilliancy for some time. The arc appeared to be a double one, by the presence of a dark band running longitudinally through it.
White streamers. Auroral bow believed to be near the earth.
Occasional streamers of equally pure white light ran upwards from either end of the bow. The moon was only a day old, but the landscape was lighted up as if by the full moon; and the effect of Kyle Akin lighthouse, the numerous surrounding islands, and the still sea between was a true thing of beauty. The display itself formed a great contrast to the more brilliant but restless forms of Auroræ generally seen. I particularly noticed a somewhat misty and foggy look about the brilliant arc, giving it almost a solid appearance. The space of sky between the horizon and the lower edge of the arc was of a deep indigo colour, probably the effect of contrast. I had a strong impression that the bow was near to the earth, and was almost convinced that the eastern end and some fleecy clouds in which it was involved were between myself and the peaks of some distant mountains.
I have not seen any other account of this Aurora, of which I was able at the time to obtain a sketch. This is reproduced on Plate VII. It was a lovely sight, and wonderfully unlike the cloud-accompanied and crimson Auroræ which I had seen in the South.
It is noticed in Parry’s ‘Third Voyage’ that the lower edge of the auroral arch is generally well defined and unbroken, and the sky beneath it so exactly like a dark cloud (to him often of a brownish colour), that nothing could convince to the contrary, if the stars, shining through with undiminished lustre, did not discover the deception.
No trace of brown colour in segment of sky below the arc.
I saw no trace of brown colour. The segment below the arch resting on the horizon was of a deep indigo colour.
Plate VII.
Dr. Allnatt’s Aurora, June 9th, 1876.
Dr. Allnatt’s Aurora, June 9, 1876. Band of auroral light appeared. Streaks of cirro-stratus divided the Aurora. Want of electric manifestations attributed to absence of sun-spots.