Auroræ: Their Characters and Spectra

CHAPTER V.. Some Qualities of the Aurora: Pp. 33-51.

Some qualities of the Aurora: pp. 33-51.

Noises attending Auroræ: pp. 33, 34.

Colours of Aurora: pp. 35-37.

Height of Aurora: pp. 37-40.

Phosphorescence attending Aurora: pp. 41-44.

Aurora and Ozone: pp. 44, 45.

Polarization of Aurora light: pp. 45, 46.

Number of Auroræ: p. 46.

Duration of Aurora: p. 47.

Travelling of Auroræ (Donati): pp. 47, 48.

Geographical distribution of Auroræ (Fritz and Loomis): pp. 48, 49.

Extent and principal zone of the Aurora: pp. 50, 51.

CHAPTER VI.. Aurora in Connexion With Other Phenomena: Pp. 52-69.

Aurora in connexion with other Phenomena: pp. 52-69.

Auroræ and Clouds: pp. 52-54.

Aurora and Thunder-storms: pp. 54, 55.

Aurora and Magnetic Needle: pp. 55-58.

Auroræ, Magnetic Disturbances, and Sun-spots: pp. 58-62.

Aurora and Electricity: pp. 62-64.

Aurora and Meteoric Dust: pp. 64, 65.

Aurora and Planets Venus and Jupiter: pp. 66, 67.

Aurora and Zodiacal Light: pp. 67-69.

CHAPTER VII.. Aurora-Like Patches on the Partially-Eclipsed Moon: Pp. 70-77.

Aurora-like patches on the partially-eclipsed Moon: pp. 70-77.

CHAPTER VIII.

Aurora and Solar Corona: pp. 78-81.

CHAPTER IX.

Supposed Causes of the Aurora: pp. 82-87.

Prof. Lemström’s Theory: pp. 87, 88.

Theories of MM. Becquerel and De la Rive: p. 88.

M. Planté’s electric experiments: pp. 89, 90.

PART II.. The Spectrum of the Aurora.

THE SPECTRUM OF THE AURORA.

CHAPTER X.

Spectroscope adapted for the Aurora: pp. 91-93.

Spectrum of Aurora described: pp. 94-100.

Flickering of the green line: p. 100.

Mr. Backhouse’s graphical spectra of four Auroræ: p. 101.

Lord Lindsay’s Aurora-spectrum, October 21, 1870: p. 102.

Spectrum of the Aurora Australis: pp. 103, 104.

Professor Piazzi Smyth’s Aurora-spectra: p. 104.

Author’s Catalogue of the Auroral lines: pp. 104-106.

Theories in relation to the Aurora and its spectrum: pp. 106, 107.

CHAPTER XI.

The comparison of some Tube and other Spectra with the Spectrum of the Aurora: pp. 108-120.

Hydrogen-tube: pp. 108-110.

Carbon- and oxygen-tubes: pp. 110-114.

Geissler mercury-tube and barometer mercurial vacuum: pp. 114, 115.

Air-tubes: pp. 115, 116.

Phosphorescent tube: pp. 116, 117.

Spark in air: p. 117.

Spark over water: p. 117.

Phosphoretted-hydrogen flame: pp. 117, 118.

Iron-spectrum: p. 118.

Spectrum of mercury: p. 119.

Table of coincidences: p. 119.

CHAPTER XII.

Notes on Professor Ångström’s Theory of the Aurora-spectrum: pp. 121-127.

CHAPTER XIII.

The Oxygen-spectrum in relation to the Aurora (Procter and Schuster): pp. 128-131.

PART III.

MAGNETO-ELECTRIC EXPERIMENTS IN CONNEXION WITH THE AURORA.

INTRODUCTION: pp. 133-135.

CHAPTER XIV.

Examination of Geissler-tubes under action of the Magnet: pp. 136-146.

Nitrogen-tubes: pp. 136, 137.

Oxygen-tubes: p. 138.

Hydrogen-tubes: pp. 138, 139.

Water-gas tube: p. 139.

Ammonia-tube: pp. 139, 140.

Carbonic-acid tube: p. 140.

Chlorine-tubes: pp. 140, 141.

Iodine-tubes: pp. 141-143.

Bromine-tubes: pp. 143, 144.

Silicic fluoride-tubes: p. 144.

Sulphuric-acid tubes: pp. 144, 145.

Sulphur-tube: pp. 145, 146.

CHAPTER XV.. Effect of Magnet on a Capillary Glass Tube: Pp. 147, 148.

Effect of Magnet on a capillary Glass Tube: pp. 147, 148.

Action of magnet on a bar of heavy glass: pp. 147, 148.

CHAPTER XVI.

Effect of Magnet on wide Air (Aurora) tube: pp. 149-153.

Stratification (note on): pp. 149, 150.

Effect of magnet on Plücker (air-) tube: pp. 150-152.

Effect of magnet on Plücker tube (tin chloride): pp. 152, 153.

Effect of magnet on tin-chloride Geissler tube: p. 153.

CHAPTER XVII.. Effect of Magnet on Bulbed Phosphorescent Tube: Pp. 154-156.

Effect of Magnet on bulbed Phosphorescent Tube: pp. 154-156.

Effect of magnet on small phosphorescent (powder) tubes: pp. 156, 157.

Lighting-up tubes with one wire only (Marquis of Salisbury’s observations): pp. 157, 158.

CHAPTER XVIII.. Action of the Magnet on the Electric Spark: Pp. 159, 160.

Action of the Magnet on the Electric Spark: pp. 159, 160.

CHAPTER XIX.

The Discharge in vacuo in Larger Vessels, and Magnetic Effects thereon: pp. 161-165.

Some of Baron Reichenbach’s magnetic researches tested: pp. 165, 166.

Summary of the foregoing Experiments and their Results: p. 167.

CHAPTER XX.. Some Concluding Remarks: Pp. 168-171.

Some concluding Remarks: pp. 168-171.

APPENDICES.

A. References to some Works and Essays on the Aurora: pp. 173, 174.

B. Extracts from the Manual and Instructions for the (English) Arctic Expedition, 1875: pp. 175-181.

C. Extracts from Parliamentary Blue-book, containing the “Results derived from the Arctic Expedition, 1875-76:” pp. 182-188.

D. Aurora and Ozone: pp. 189-193.

E. Dr. Vogel’s Inquiries into the Spectrum of the Aurora: pp. 194-207.

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.

THE AURORA AND ITS CHARACTERS.

CHAPTER I.

THE AURORA AS KNOWN TO THE ANCIENTS.

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, quum velut corona cingente introrsus igneus cœli recessus est similis effossæ in orbem speluncæ. Sunt Pithitæ, quum magnitudo vasti rotundique ignis dolio similis, vel fertur vel in uno loco flagrat. Sunt Chasmata, 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.

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.”

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 of space. There are Pithitæ, when the expanse of a vast and rounded fire similar to a tub (dolium) is either carried about or glows in one spot.

“There are Chasmata, when a certain portion of the sky opens, and gaping displays the flame as in a porch. The colours also of all these are many. Certain are of the brightest red, some of a flitting and light flame-colour, some of a white light, others shining, some steadily and yellow without eruptions or rays.

“Amongst these we may notice, what we frequently read of in history, the sky is seen to burn, the glow of which is occasionally so high that it may be seen amongst the stars themselves, sometimes so near the Earth (humilis) that it assumes the form of a distant fire. Under Tiberius Cæsar the cohorts ran together in aid of the colony of Ostia as if it were in flames, when the glowing of the sky lasted through a great part of the night, shining dimly like a vast and smoking fire.”

From the above passages many striking particulars of the Aurora may be gathered; and by the division of the forms of Aurora into classes it is evident they were, at that period, the subject of frequent observation. The expression “et quod frequenter in historiis legimus” shows, too, that the phenomena of Auroral displays were a matter of record and discussion with the writers of the day.

Various forms of Aurora may be recognized in the passages from Chap. xiv.; while in those from Chap. xv. a careful distinction is drawn between the Auroræ seen in the zenith or the upper regions of the sky, and those seen on the horizon or apparently (and no doubt in some cases actually) near the Earth’s surface.

The description of the cohorts running to the fire only to find it an Aurora, calls to mind the many similar events happening in our own days. Not, however, but that a mistake may sometimes occur in an opposite direction. In the memoirs of Baron Stockmar an amusing anecdote is related of one Herr von Radowitz, who was given to making the most of easily picked up information. A friend of the Baron’s went to an evening party near Frankfort, where he expected to meet Herr von Radowitz. On his way he saw a barn burning, stopped his carriage, assisted the people, and waited till the flames were nearly extinguished. When he arrived at his friend’s house he found Herr von Radowitz, who had previously taken the party to the top of the building to see an Aurora, dilating on terrestrial magnetism, electricity, and so forth. Radowitz asked Stockmar’s friend, “Have you seen the beautiful Aurora Borealis?” He replied, “Certainly; I was there myself; it will soon be over.” An explanation followed as to the barn on fire: Radowitz was silent some ten minutes, then took up his hat and quietly disappeared.

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