Auroræ: Their Characters and Spectra

BY J. RAND CAPRON, F.R.A.S.
“And now the Northern Lights begin to burn, faintly at first, like sunbeams playing in the waters of the blue sea. Then a soft crimson glow tinges the heavens. There is a blush on the cheek of night. The colours come and go; and change from crimson to gold, from gold to crimson. The snow is stained with rosy light. Twofold from the zenith, east and west, flames a fiery sword; and a broad band passes athwart the heavens, like a summer sunset. Soft purple clouds come sailing over the sky, and through their vapoury folds the winking stars shine white as silver. With such pomp as this is Merry Christmas ushered in, though only a single star heralded the first Christmas.”—Longfellow.
LONDON: E. & F. N. SPON, 46 CHARING CROSS. NEW YORK: 446 BROOM STREET. 1879.

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.


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.