236 Causes of the Aurora Borealis. 



l 



while the more quiet minded and careful observer has discovered 

 that they are often preludes to high winds and tempests. 



Many theories have been proposed to account for the phenomenon, 

 but the explanations are unsatisfactory ; the inquiry still arises why 

 the aurora is visible in the temperate and frigid zones, while it is never 

 seen within the tropics — why it is so uncertain in its returns, observing 

 no periodical law — why it is at one time so brilliant, and at otner times 

 only a pale gleam in the edge of the horizon — why, in the temperate 

 latitudes, it appears in an arc of the northern hemisphere, while in the 

 arctic circle it is always seen in the south — why it is visible as the 

 twilight appears, and generally extinguished near or soon after mid- 

 night — and why it is seen shooting and corruscating in streams and 

 spires, emulating the lightning in vividness, and the rainbow in col- 

 oring ; and again, silently rising in a compact majestic arch of stea- 

 dy white light, apparently durable and immovable, and yet so evanes- 

 cent, that while you look upon it, it is not. 



The various aspects of the boreal lights in these latitudes are fa- 

 miliar to every one, although it may not be equally well known, that 

 they increase in vividness, splendor and frequency near and within 

 the polar circle, Mavpertuis remarks, that in Lapland, " the sky 

 was sometimes tinged with so deep a red that the constellation Orion 

 looked as though it were dipped in blood, and that the people fa" c,e J 

 they saw armies engaged, fiery chariots, and a thousand prodigies 

 and that the red colors were deemed a presage of misfortune. 

 Gmelin relates that in Siberia, between the Lena and Jenesei, on the 

 confines of the icy sea, " the spectral forms appear like rushing ar- 

 mies ; the hissing crackling noises of those aerial fireworks so terrify 

 the dogs and the hunters that they fall prostrate on the ground, and 

 will not move, while ' the ranging host is passing.' " 



Kerguden describes " the night as brilliant as the day," «• laL 

 50°, between Iceland and the Ferro Islands, " the heavens being on 

 fire with flames of red and white light, changing to columns and 

 arches, and at length confounded in a brilliant chaos of cones, pyra- 

 mids, radii, sheaves, arrows, and globes of fire."f 



But the evidence of Capt. Parry is of more value than that of the 

 earlier travelers, as he examined the phenomenon under the most »- 



> 

 * 



* Memoir on the measure of a degree, at the polar cirelp 

 t Kergiielen's voyage to the North. 



