The
following is the description given by Humboldt in "Cosmos":--
"An aurora borealis is always preceded by the formation in the horizon
of a sort of nebulous veil, which slowly ascends to a height of 4 deg.,
6 deg., 8 deg., and even to 10 deg.. It is towards the magnetic meridian
of the place that the sky, at first pure, begins to get brownish. Through
this obscure segment, the color of which passes from brown to violet,
the stars are seen, as through a thick fog. A wider arc, but one of
brilliant light, at first white, then yellow, bounds the dark segment.
Sometimes the luminous arc appears agitated, for hours together, by a
sort of effervescence, and by a continuous change of form, before the
rising of the rays and columns of light, which ascend as far as the
zenith. The more intense the emission of the polar light, the more
vivid are its colors, which, from violet and bluish white, pass through
all the intermediate shades of green and purple-red. Sometimes the
columns of light appear to come out of the brilliant arc mingled with
blackish rays, resembling a thick smoke; sometimes they rise
simultaneously from different points of the horizon, and unite
themselves into a sea of flames, the magnificence of which no painting
could express; for, at each instant, rapid undulations cause their form
and brilliancy to vary.
Pages:
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292