Auroræ: Their Characters and Spectra. J. Rand Capron
and sharp red and green lines, which mainly characterize the spectrum, are as yet unassociated with any known analogue.
With these views, and to incite to further and closer observations, I have been induced to publish the present volume as a sort of Auroral Guide. For much of the history of the Aurora I am indebted to, and quote from former articles and records, including the two excellent Encyclopædic ones before referred to. Mr. Procter, Mr. Backhouse, and my friend Mr. W. H. Olley have each kindly furnished me with much in the way of information and suggestion. Dr. Schuster has lent me tubes showing the true oxygen spectrum; while Herr Carl Bock, the Norwegian naturalist, has enabled me to reproduce a veritable curiosity, viz. a picture in oil painted by the light of a Lapland Aurora. The experiments detailed in Part III. were suggested by the earlier ones of De la Rive, Varley, and others, and demonstrate the effect of the magnet on electric discharges. For assistance in these I am indebted to my friend Mr. E. Dowlen.
The illustrations are mainly from original drawings of my own. Those from other sources are acknowledged. Messrs. Mintern have well reproduced in chromo-lithography the coloured drawings illustrating the Auroræ, moon-patches, &c.
LIST OF PLATES.
| Plate. | |||
|---|---|---|---|
| I. | The Aurora during the Ice-pressure | To face page | 14 |
| II. | Aurora seen by Dr. Hayes, 6th January, 1861 | ” ” | 16 |
| III. | Aurora, Guildford, Oct. 24, 1870 | ” ” | 18 |
| IV. | Aurora, Guildford, Feb. 4, 1872; Eclipsed Moon, Aug. 23, 24, 1877 | ” ” | 20 |
| V. | Corona, Graphical Auroræ, Zodiacal Light, &c. | ” ” | 21 |
| VI. | Aurora, Guildford, Feb. 4, 1874; Spectrum des Nordlichts (Vogel) | ” ” | 22 |
| VII. | Aurora, Kyle Akin, Isle of Skye, Sept. 11, 1874 | ” ” | 24 |
| VIII. | Herr Carl Bock’s Lapland Aurora, Oct. 3, 1877 | ” ” | 25 |
| IX. | Compared Aurora and other Spectra. Loomis’s curves of Auroras, Magnetic Declination, and Solar Spots | ” ” | 59 |
| X. | Spectroscope, Micrometer, Tubes | ” ” | 91 |
| XI. | Aurora-spectra, Candle-spectrum | ” ” | 102 |
| XII. | Aurora-spectrum, Solar spectrum, and Candle-spectrum | ” ” | 104 |
| XIII. | Vogel’s Aurora-lines, Aurora-lines near G, and in the red and green | ” ” | 108 |
| XIV. | Aurora, Hydrocarbons, Oxygen | ” ” | 110 |
| XV. | Aurora and Air-tubes, &c. | ” ” | 115 |
| XVI. | Aurora, Phosphoretted Hydrogen, Iron, &c. | ” ” | 117 |
| XVII. | Effect of Magnet on Tubes and Spark | ” ” | 134 |
| XVIII. | Same, and Oxygen-spectrum | ” ” | 154 |
PART I.
THE AURORA AND ITS CHARACTERS.
CHAPTER I.
THE AURORA AS KNOWN TO THE ANCIENTS.
Seneca’s ‘Quæstiones Naturales,’ Lib. I. c. xiv. Description of Auroræ.
In Seneca’s ‘Quæstiones Naturales,’ Lib. I. c. xiv., we find the following:—“Tempus est, alios quoque ignes percurrere, quorum diversæ figuræ sunt. Aliquando emicat stella, aliquando ardores sunt, aliquando fixi et hærentes, nonnunquam volubiles. Horum plura genera conspiciantur. Sunt Bothynoë[1], quum velut corona cingente introrsus igneus cœli recessus est similis effossæ in orbem speluncæ. Sunt Pithitæ[2], quum magnitudo vasti rotundique ignis dolio similis, vel fertur vel in uno loco flagrat. Sunt Chasmata[3], quum aliquod cœli spatium desedit, et flammam dehiscens, velut in abdito, ostentat. Colores quoque omnium horum plurimi sunt. Quidam ruboris acerrimi, quidam evanidæ ac levis flammæ, quidam candidæ lucis, quidam micantes, quidam æqualiter et sine eruptionibus aut radiis fulvi.
…
Seneca, c. xv.
C. xv. “Inter hæc ponas licet et quod frequenter in historiis legimus, cœlum ardere visum: cujus nonnunquam tam sublimis ardor est ut inter ipsa sidera videatur, nonnunquam tam humilis ut speciem longinqui incendii præbeat.
“Sub Tiberio Cæsare cohortes in auxilium Ostiensis coloniæ cucurrerunt, tanquam conflagrantis, quum cœli ardor fuisset per magnam partem noctis, parum lucidus crassi fumidique ignis.”
Translation.
We may translate this:—“It is time other fires also to describe, of which there are diverse forms.
“Sometimes a star shines forth; at times there are fire-glows, sometimes fixed and persistent, sometimes flitting. Of these many sorts may be distinguished. There are Bothynoë, when, as within a surrounding corona, the fiery recess of the sky is like to a cave dug out