PRINTED BY TAYLOR AND FRANCIS,
RED LION COURT, FLEET STREET.

TO
Prof. CHARLES PIAZZI SMYTH, F.R.S.E.,
ASTRONOMER ROYAL FOR SCOTLAND,
ONE OF THE EARLIEST SPECTROSCOPIC OBSERVERS
OF
THE AURORA AND ZODIACAL LIGHT,
THIS VOLUME
IS
RESPECTFULLY DEDICATED
BY
THE AUTHOR.

PREFACE.

Probably few of the phenomena of Nature so entirely charm and interest scientific and non-scientific observers alike as the Aurora Borealis, or “Northern Lights” as it is popularly called. Whether contemplated as the long low quiescent arc of silver light illuminating the landscape with a tender radiance, as broken clouds and columns of glowing ruddy light, or as sheaves of golden rays, aptly compared by old writers to aerial spears, such a spectacle cannot fail at all times to be a subject of admiration, in some cases even of awe.

Hence it is no wonder that the Aurora has always received a considerable amount of attention at the hands of scientific men. Early explorers of the Arctic Regions made constant and important observations of it and its character; and the list of references to works given in the Appendix will show how often it formed the subject of monographs and communications to learned Societies. The early contributions seem relatively more numerous than those of a later date; and the substance of them will be found well summed up in Dr. Brewster’s ‘Edinburgh Encyclopædia’ (1830), article “Aurora.” A most complete and able epitome of our more recent experience and knowledge of the Aurora and its spectrum has been contributed by my friend Mr. Henry R. Procter to the present (9th) edition of the ‘Encyclopædia Britannica,’ article “Aurora Polaris.” It is, however, a drawback to Encyclopædic articles that their matter is of necessity condensed, and that they rarely have the very desirable aid of drawings and engravings to illustrate their subjects. In spite, therefore, of the exhaustive way, both as to fact and theory, in which the contributor to the ‘Encyclopædia Britannica’ has realized his task, it seemed to me there was still room left for a popular treatise, having for its object the description of Auroræ, their characters and spectra. The question of the Aurora spectrum seems the more worthy of extended discussion in that it still remains an unsolved problem. In spite of the observations and researches of Ångström, Lemström, and Vogel abroad, and of Piazzi Smyth, Herschel, Procter, Backhouse, and others at home, the goal is not yet reached; for while the faint and more refrangible lines are but doubtfully referred to air, the bright 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.

TABLE OF CONTENTS.

LIST OF PLATES.

PART I.
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[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.

…

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.”