Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1Humboldt, Alexander von
History
Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1
Humboldt, Alexander von
Astronomy; Cosmography; Physical geography; Science -- History
[footnote] **[Professor Challis of Cambridge, states that in the Aurora of
October 24th, 1847, the streamers all converged toward a single point of the
heavens, situated in or very near a vertical circle passing through the
magnetic pole. Around this point a corona was formed, the rays of which
diverged in all directions from the center, leaving a space free from light:
its azimuth was 18 degrees 41' from south to east, and its altitude 69
degrees 54'. See Professor Challis, in the 'Athenaeum', Oct. 31, 1847.] --
Tr.
In the northern latitudes,
p 196
in the immediate vicinity of the magnetic pole, the smoke-like conical
segment appears less dark, and sometimes is not even seen. Where the
horizontal force is the weakest, the middle of the luminous arch deviates
the most from the magnetic meridian.
The luminous arch remains sometimes for hours together flashing and kindling
in ever-varying undulations, before rays and streamers emanate from it, and
shoot up to the zenith. The more intense the discharges of the northern
light, the more bright is the play of colors, through all the varying
gradations from violet and bluish white to green and crimson. Even in
ordinary electricity excited by friction, the sparks are only colored in
cases where the explosion is very violent after great tension. The magnetic
columns of flame rise eithr singly from the luminous arch, blended with
black rays similar to thick smoke, or simultaneously in many opposite points
of the horizon, uniting together to torm a flickering sea of flame, whose
brilliant beauty admits of no adequate description, as the luminous waves
are every moment assuming new and varying forms. The intensity of this
light is at times so great, that Lowenorn (on the 29th of June, 1786)
recognized the coruscation of the polar light n bright sunshine. Motion
renders the phenomenon more visible. Round the point in the vault of heaven
which corresponds to the direction of the inclination of the needle, the
beams unite together to form the so-called corona, the crown of the northern
light, which encircles the summit of the heavenly canopy with a milder
radiance and unflickering emanations of light. It is only in rare instances
that a perfect crown or circle is formed, but on its completion the
phenomenon has invariably reached its maximum, and the radiations become
less frequent, shorter, and more colorless. The crown and the luminous
arches break up, and the whole vault of heaven becomes covered with
irregularly-scattered, broad, faint, almost ashy-gray luminous immovable
patches, which in their turn disappear, leaving nothing but a trace of the
dark, smoke-like segment on the horizon. There often remains nothing of the
whole spectacle but a white, delicate cloud with feathery edges, or divided
at equal distances into small roundish groups like cirio-cumuli.
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