Auroræ: Their Characters and Spectra. J. Rand Capron
of light rolls slowly from one side to the other. It begins to grow clear over the ice; some of its groups are discernible. The arch is still distant from the zenith, a second detaches itself from the dark segment, and this is gradually succeeded by others. All now rise towards the zenith; the first passes beyond it, then sinks slowly towards the northern horizon, and as it sinks loses its intensity. Arches of light are now stretched over the whole heavens; seven are apparent at the same time on the sky, though of inferior intensity. The lower they sink towards the north the paler they grow, till at last they utterly fade away. Often they all return over the zenith, and become extinct just as they came.
Band of light appears. Second band and rays.
“It is seldom, however, that an Aurora runs a course so calm and so regular. The typical dark segment, which we see in treatises on the subject, in most cases does not exist. A thin bank of clouds lies on the horizon. The upper edge is illuminated; out of it is developed a band of light, which expands, increases in intensity of colour, and rises to the zenith. The colour is the same as in the arch, but the intensity of the colour is stronger. The colours of the band change in a never-ceasing play, but place and form remain unaltered. The band is broad, and its intense pale green stands out with wonderful beauty on the dark background. Now the band is twisted into many convolutions, but the innermost folds are still to be seen distinctly through the others. Waves of light continually undulate rapidly through its whole extent, sometimes from right to left, sometimes from left to right. Then, again, it rolls itself up in graceful folds. It seems almost as if breezes high in the air played and sported with the broad flaming streamers, the ends of which are lost far off on the horizon. The light grows in intensity, the waves of light follow each other more rapidly, prismatic colours appear on the upper and lower edge of the band, the brilliant white of the centre is enclosed between narrow stripes of red and green. Out of one band have now grown two. The upper continually approaches the zenith, rays begin to shoot forth from it towards a point near the zenith to which the south pole of the magnetic needle, freely suspended, points.
Corona formed.
“The band has nearly reached it, and now begins a brilliant play of rays lasting for a short time, the central point of which is the magnetic pole—a sign of the intimate connexion of the whole phenomenon with the magnetic forces of the earth. Round the magnetic pole short rays flash and flare on all sides, prismatic colours are discernible on all their edges, longer and shorter rays alternate with each other, waves of light roll round it as a centre. What we see is the auroral corona, and it is almost always seen when a band passes over the magnetic pole. This peculiar phenomenon lasts but a short time. The band now lies on the northern side of the firmament, gradually it sinks, and pales as it sinks; it returns again to the south to change and play as before. So it goes on for hours, the Aurora incessantly changes place, form, and intensity. It often entirely disappears for a short time, only to appear again suddenly, without the observers clearly perceiving how it came and where it went; simply, it is there.
Single-rayed band.
“But the band is often seen in a perfectly different form. Frequently it consists of single rays, which, standing close together, point in an almost parallel direction towards the magnetic pole. These become more intensely bright with each successive wave of light; hence each ray appears to flash and dart continually, and their green and red edges dance up and down as the waves of light run through them. Often, again, the rays extend through the whole length of the band, and reach almost up to the magnetic pole. These are sharply marked, but lighter in colour than the band itself, and in this particular form they are at some distance from each other. Their colour is yellow, and it seems as if thousands of slender threads of gold were stretched across the firmament. A glorious veil of transparent light is spread over the starry heavens; the threads of light with which this veil is woven are distinctly marked on the dark background; its lower border is a broad intensely white band, edged with green and red, which twists and turns in constant motion. A violet-coloured auroral vapour is often seen simultaneously on different parts of the sky.
Aurora in stormy weather. Fragments.
“Or, again, there has been tempestuous weather, and it is now, let us suppose, passing away. Below, on the ice, the wind has fallen; but the clouds are still driving rapidly across the sky, so that in the upper regions its force is not yet laid. Over the ice it becomes somewhat clear; behind the clouds appears an Aurora amid the darkness of the night. Stars twinkle here and there; through the opening of the clouds we see the dark firmament, and the rays of the Aurora chasing one another towards the zenith. The heavy clouds disperse, mist-like masses drive on before the wind. Fragments of the northern lights are strewn on every side: it seems as if the storm had torn the Aurora bands to tatters, and was driving them hither and thither across the sky. These threads change form and place with incredible rapidity. Here is one! lo, it is gone! Scarcely has it vanished before it appears again in another place. Through these fragments drive the waves of light: one moment they are scarcely visible, in the next they shine with intense brilliancy. But their light is no longer that glorious pale green; it is a dull yellow. It is often difficult to distinguish what is Aurora and what is vapour; the illuminated mists as they fly past are scarcely distinguishable from the auroral vapour which comes and goes on every side.
Bands. Rays reach the pole. No noise.
“But, again, another form. Bands of every possible form and intensity have been driving over the heavens. It is now eight o’clock at night, the hour of the greatest intensity of the northern lights. For a moment some bundles of rays only are to be seen in the sky. In the south a faint, scarcely visible band lies close to the horizon. All at once it rises rapidly, and spreads east and west. The waves of light begin to dart and shoot, some rays mount towards the zenith. For a short time it remains stationary, then suddenly springs to life. The waves of light drive violently from east to west, the edges assume a deep red and green colour, and dance up and down. The rays shoot up more rapidly, they become shorter; all rise together and approach nearer and nearer to the magnetic pole. It looks as if there were a race among the rays, and that each aspired to reach the pole first. And now the point is reached, and they shoot out on every side, to the north and the south, to the east and the west. Do the rays shoot from above downwards, or from below upwards? Who can distinguish? From the centre issues a sea of flames: is that sea red, white, or green? Who can say? It is all three colours at the same moment! The rays reach almost to the horizon: the whole sky is in flames. Nature displays before us such an exhibition of fireworks as transcends the powers of imagination to conceive. Involuntarily we listen; such a spectacle must, we think, be accompanied with sound. But unbroken stillness prevails; not the least sound strikes on the ear. Once more it becomes clear over the ice, and the whole phenomenon has disappeared with the same inconceivable rapidity with which it came, and gloomy night has again stretched her dark veil over everything. This was the Aurora of the coming storm—the Aurora in its fullest splendour. No pencil can draw it, no colours can paint it, and no words can describe it in all its magnificence.”
A reproduction of the woodcut in Payer’s ‘Austrian Arctic Voyages,’ illustrating some of the features of the above description, will be found on Plate I.
In the ‘Edinburgh Encyclopædia,’ article “Aurora,” we find:—
Descriptions of Auroræ in high Northern latitudes.
“In high Northern latitudes the Auroræ Boreales are singularly resplendent, and even terrific.
“They frequently occupy the whole heavens, and, according to the testimony of some, eclipse the splendour of stars, planets, and moon, and even of the sun itself.
In Siberia.
“In the south-eastern districts of Siberia, according to the description of Gmelin, cited and translated by Dr. Blagden (Phil. Trans. vol. lxxiv. p. 228), the Aurora is described to begin with single bright pillars, rising in the north, and almost at the same time in the north-east, which, gradually increasing, comprehend a large space of the heavens, rush about from place to place with incredible velocity, and finally almost cover the whole sky up to the zenith, and produce an appearance as if a vast tent were expanded in the heavens, glittering with gold, rubies, and sapphires. A more beautiful spectacle cannot be painted; but whoever should see such