The duration of the aurora is very various. Some times it is formed and disappears in the course of a few minutes. At othcr times, it lasts during the whole night, or even for two or three days together ; and Muschenbroek observed one in 1734, that lasted teu days and nights successively ; and another in 1735, that lasted from the 22d to the 31st of March. The lucid columns are so transparent, that stars of the first and second magnitude are easily seen through them ; these'also frequently shine through the white border of the horizontal cloud, and sometimes, though rare ly, through the opaque.cloud itself. But many parts of the luminous substance are so thin, that the smal lest stars which are visible to the naked eye may be distinguished through them.
, In high northern latitudes, as those of Sweden, Lapland, and Siberia, the aurora; borealcs are singu larly resplendent, and even terrific. They frequently occupy the whole of the heavens ; and, according to the testimony of Maupertuis, Middleton, Krafft, and others, eclipse the splendour of the stars, planets, and moon, and sometimes even of the sun himself. In the north-eastern districts of Siberia, according to the de scription of Gmelin, cited and translated by Dr Blag den, (Phil. Trans. vol. .p. 228.) the aurora is observed 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 appear ance as if a vast tent was expanded in the heavens, glittering with gold, rubies, and sapphire. A more beautiful spectacle cannot be painted ; but whoever should see such a horthern light for the first time, could not behold it without terror. Fur, however fine the illumination may be, it is attended, as I have learned from the relation of many persons, with such a hissing, cracking, and rushing noise through air, as if the largest fire-works wt re playing off. To de scribe what they then hear, they make use of the ex pression spoluchi chogjat, that is, the raging host is passing. The hunters who pursue the white and blue foxes in the confines of the Icy sea, are often overtaken in their course by these northern lights..
Their dogs are then so much frightened that they will not move, but lie obstinately on the ground till the noise has passed. Commonly clear and calm wea
ther follows this kind of northern lights. I have heard this account not from one person only, but confirmed by the uniform testimony of many who have spent part of several years in these very northern regions, and inhabited different countries from the Yenisei to the Lena ; so that no doubt of its truth can remain. This seems, indeed, to be the real birth-place of the aurora borealis.
Maupertuis describes a veryremarkable aurora which he saw at Oswer-Zornea, on the 18th December 1736, and which he says excited his admiration, not withstanding the many extraordinary appearances of this kind to which he had been accustomed to in the Arctic regions. An extensive region of the heavens towards the south appeared tinged of so lively a red, that the whole constellation Orion seemed as if dyed in blood. This light was for some time fixed, but soon became moveable ; and after having successively assumed all the tints of violet and blue, it formed a dome, of which the summit nearly approached the zenith in the south-west. Its splendour was so great, as to be in no degree affected by the strong light of the moon. Maupertuis adds, that lie observed only two of these red northern lights in Lapland, which are • of very rare occurrence in that country, although the aurora there assumes a great variety of tints ; hence they are considered by the natives as of portentous omen, and as the forerunners of some great calamity.
This account of the noises attending the aurora borealis has been corroborated by other testimonies. They have been heard at Hudson's Bay, and in Swe den ; and Muschenbroek mentions, that the Green land whale fishers assured him they had frequently heard the noise of the aurora borealis ; but adds, that no person in Holland had ever experienced this phe nomenon. Mr Cavallo, however, declares, that he has repeatedly heard a crackling sound proceeding from the aurora borealis. (Elem. 2fNat. and Phil. vol. iii. p. 449.) And Mr Nairne mentions, that, being in Northampton at the time when the northern lights were remarkably bright, he is con ident he perceived a hissing or whizzing sound. Mr Belknap, also, of Dover, in New Hampshire, North America, testifies to the same fact. Amer. Trans. vol. ii. p. 196.