The Sun.
London, England, 1848-10-26 00:00:00

THE AURORA BOREALIS OF
OCTOBER 18, 1848.

(From the Liverpool Mercury of Tuesday.)
r On Wednesday evening la-t, October 18, there oc-
curred an aurora borealis, which, for length of dura-
Von, brilliance, and variety of effects, has probably
not been excelled, if equalled, for many years. it is
thought desirable to place on record some of the fea-
tures of this phenomenon, in the hope that due atten •
tion may in time be drawn to an effect of nature at
once mysterious and beautiful, and which is so much
neglected, and so rarely seen with attention even when
it occurs. The summer of 1848 has been unusually
wet and cold. The easterly winds, of which we have
generally an average of two spells in a year, which
bring fine clear weather, in summer and frost
in winter, set in about a week ago. The lath
instant was extremely cold for the season, there being
ice in many places, a rather rare thing in England in
October. During the course of the day a few slight
showers of fine snow and hail indicated the state of
the atmosphere, which became gradually free from
clouds towards sunset, after which, and as night ap-
proached, the arc of the heavens presented a cloudless
sky of intense blue.
and starry

At a quarter to seven a plain whitish light began
to diffuse itself over the northern hemisphere, em-
bracing fully 1410 degrees of the horizon, having the
north for the centre, and extending to the zenith.
This faint suffusion of light slightly dimmed the
stars which it covered, was most intense or whiter at
the extremes, east and west, and gave the southern
hemisphere an appearance of depth of blue, of dark-
ness, and brilliance of star light apparently mere
intense, but which must be attributed to the contrast.

As the evening proceeded faint vertical rays began
to shoot from the horizon towards the zenith, which
gave every indication of an appearance of this pheno-
menon of unusual magnitude. As these rays, still of
a pale colour, increased, an arc of shadowy darkness
but having evident light behind it, began to Occupy
the northern part of the horizon, extending to about
30 degrees each side of the north point.
About half-past seven the light corruscations began
to assume colours of the most delicate reds, blue
greens, and some of the most indefinable gradations,
varying in effect and intensity of light till nine o'clock,
when every accompaniment of this phenomenon in-
creased in brilliancy and effect.
The shadowy arc extended in length and altitude,
overtopping Ursa Major, and becoming double, its
light edge being surmounted by a dark ridge or arch,
which was again tipped with light, and from this last
ridge the vertical rays chiefly ascended. This shadowy
arc did not preserve its form in continuance ; it
assumed d
different altitudes, and occasionally became
indented in its surface, so as to form a series of seg-
ments of the circle. The character of the shadowy
arc was particularly noticed, because light could be
seen through it, and although the vertical rays were
seen chiefly to ascend from its edge, yet they evi-
dently ascended from beneath the horizon, because,
when one of unusual magnitude and intensity of
light arose, the shadow was not strong enough
to conceal it; it could be distinctly traced be-
hind the shadow, which appeared as a veil, to
the line of the horizon. Although coloured
rays appeared at various times, the greatest
intensity was from nine to eleven o'clock. The
central rays due north were chiefly of the pale blue
greens, lilac, pale blue, and grey; the red rays were
chiefly confined to the extreme east and west, and
were more coloured near the zenith, where a broad
expanse of the most luminous and beautiful red was
slightly purpled by its transparency showing the blue
of space beyond; this red, as it decayed, mingled
gradually and softly with the sky, becoming More
purple as the red grew weaker, till lost to vision in a
cloudy appearance at the zenith.
During the culmination of this effect a most extra-
ordinary appearance ensued; the rays had chiefly
mowed vertically, and from the horizon towards the
zenith, but they now began to move occasionally
horizontally, crossing each other with the rapidity
of lightning, and, it is believed, always from east to
west. This had a most extraordinary appearance,
and whenever it took place a corresponding change as
rapid took place at the zenith, as the illuminating
rays changed their position.

At about a quarter-past nine a splendid meteor
passed from east to west, its course being nearly
horizontal ; it was speedily exhausted, and it left the
ocular deception of a train of light after it, which is
often seen. Afterwards the moon rose and gave
increased beauty to the scene. At eleven the splen-
dour and intensity of the, rays began to decrease;
instead of the sharply-defined rays which previously
shot in streams from the edge of the shadow, and
which continued to be most dense at the extreme
east and west, broad expanses of delicate light and
colour continued to ascend from the shadowy arc
occasionally seen behind it, and gradually decreasing
till a soft blue grey light suffused the heavens as at
the beginning ; and a little after one the effect ceased,
save that a softened twilight pervaded the north, the
southern hemisphere having throughout preserved a
continued and intense darkness, unaffected even by
the slightest reflection.
The aurora borealis assumes different characters,
and may be classified into four descriptions, as fol-
lows : That which presents a dark shadowy arc,
assuming various altitudes, surrounded by a faint or
strong colourless light, but without rays proceeding
from it. Second, that which, in addition to the above,
projects rays to the zenith, which assumes various
colours, and adds the additional phenomenon of motion.
The first seldom extends to more than sixty degrees of
the horizon having the north for the centre; the second
extends to various distances, but never beyond ninety
degrees each side the north point, nor beyond the
zenith of the spectator. The third has an expansive
light, without the dark concave shadow, and without
rays—but in diffused masses ; this is the strongest
with regard to colour; their transparent masses of
brilliant reds and purples, and more dslicate tones
covering the heavens, but through which the stars
may be seen ; these masses frequently extend beyond
the zenith, and beyond 180 degrees of the horizon,
the north being the centre, the masses of colour
ceasing, changing, or pervading the sky with the
utmost rapidity. The fourth and last is rarely seen,
even by those whom habits, from whatever cause,
have led them to watch atmospheric effects at all
hours, and for many years. These are horizontal
rays of the aurora borealis, which shoot from north
to south, arising and terminating in a point; which
keep near the surface of the earth, are colourless, and
said to be accompanied by a slight rushing noise, as
of a switch gently struck through the air. The
effects of this description are exceedingly faint and
delicate, appear to be confined to the lower portions
of the atmosphere, and are unaccompanied by any
demonstrations of light or colour in the higher regions
of air.

To whatever cause the whole of these phenomena
may be ascribed, whether of electricity or any other,
we leave to those able to speculate on the subject.
We wish only to offer a few remarks on the colour of
the aurora, to show that it is simply an effect of the
common law of light, which is the origin and cause
of all colour.
Affirming pure light to be white, and the absence
of all light to be darkness or black, all gradations of
colour between are the result of the density of the
former and its admixture with the latter. This
theory is established by the agreement of the effects
with the cause, which are as follow :----Light pro-
jected into a pure atmosphere, illuminated by itself, is
colourless or white ; but the illuminated medium
through which light passes becoming more dense, it
becomes yellow, and so increases to the utmost den-
sity that light is capable of being transmitted by,
which is red, which is the most powerful of all co-
lours. The least mixture of pure white or light with
darkness produces blue; a more dense stage of
light—
namely yellow, mixed 'with darkness, is green; and
its most dense stage, or red rays, mixed -With dark-
ness, become purple. These can be modified infi-
nitely, to every possible grade of colour, every shade
of which will agree with the theory of their cause—
namely, light and darkness. As, for instance, the
least possible degree of darkness mixed with the
utmost density light is capable of, namely red, pro-
duces crimson, crimson diluted again with pure light
becomes pink, &c.
These remarks are thought necessary, because the
effects of the aurora borealis exactly coincide with the
theory here expressed, the colour of the- rays being
neither more nor less than their light (from whatever
cause) being modified by density and mixture with
darkness. This accounts for the crimson rays being
chiefly confined to the east and west, where we have
shown the light was most dense and accumulated,
the crimson being caused by the most dense or red
rays, still being so thin and transparent as to cause
the darkness or blue beyond to be dimly seen
through.
From the same cause the different rays assumed
different colours, exactly in proportion as the light
was more or less dense, and capable of overpowering
or amalgamating with the darkness it penetrated.
The reason why the rays nearer the earth were more
faint in colour, and those more distant more intense,
is accounted for entirely on the principle of density;
the same that causes the zenith of daylight to be
more blue from thinness, and the sun to be red at
setting.
We have endeavoured, with some difficulty, to
render our account of this phenomenon as familiar as
possible, and free from technical terms, being desirous
that all classes of our readers should avail themselves
of a description by an eye-witness of this extraor-
dinary and beautiful effect.

MARBLES FOR THE MUSEIIAL—The large quantity
of ancient marbles which have recently been brought to
this country from Bombay, by one of her Majesty's
ships, for the British Museum, have been deposited in
that establishment. The packages in which they were
contained were fifty-five in number.