These splendid meteors are generally considered as the result of a
combination of the two powers of magnetism and electricity. When the
_light_, or _aurora_, appears chiefly in the north part of the heavens,
it is called the _aurora borealis_, or northern lights; and when chiefly
in the south part, the =aurora australis=, or southern lights. Where the
coruscation is more than ordinarily bright and streaming, which,
however, seldom occurs in the north, it is denominated =lumen boreale=;
and where these streams have assumed a decided curvature, like that of
the rainbow, they are distinguished by the name of luminous arches.
The aurora is chiefly visible in the winter season, and in cold weather.
It is usually of a reddish color, inclining to yellow, and sends out
frequent coruscations of pale light, which seem to rise from the horizon
in a pyramidal, undulating form, shooting with great velocity up to the
zenith. It never appears near the equator; but of late years has
frequently been seen toward the south pole. The =aurora borealis= has
appeared at some periods more frequently than at others. This phenomenon
was so rare in England, or so little regarded, that its appearance was
not recorded in the English annals between a remarkable one observed on
the fourteenth of November, 1554, and a very brilliant one on the sixth
of March, 1716, and the two succeeding nights, but which was much
strongest on the first night. Hence it may be inferred, that the state
of either the air or earth, or perhaps of both, is not at all times
fitted for its production.
The extent of these appearances is surprisingly great. The very
brilliant one referred to above was visible from the west of Ireland to
the confines of Russia, and the east of Poland, extending over, at the
least, thirty degrees of longitude, and, from about the fiftieth degree
of latitude, over almost all the northern part of Europe. In every
place, it exhibited, at the same time, the same wonderful features. The
elevation of these lights is equally surprising: an =aurora borealis=
which appeared on the sixteenth of December, 1737, was ascertained, by
means of thirty computations, to have an average hight from the earth of
one hundred and seventy-five leagues, equal to four hundred and
sixty-four English miles.
Captain Cook, in his first voyage round the world, observed that these
coruscations are frequently visible in southern latitudes. On the
sixteenth of September, 1770, he witnessed an appearance of this kind
about ten o’clock at night, consisting of a dull, reddish light, and
extending about twenty degrees above the horizon. Its extent was very
different at different times, but it was never less than eight or ten
points of the compass. Rays of light, of a brighter color, passed
through and without it; and these rays vanished and were renewed nearly
in the same time as those in the =aurora borealis=, but had little or no
vibration. Its body bore south-south-east from the ship, and continued,
without any diminution of its brightness, till twelve o’clock, when the
observers retired. The ship was at this time within the tropic of
Capricorn.
On the seventeenth of February, 1773, during his second voyage, Captain
Cook speaks of a beautiful phenomenon that was observed in the heavens.
“It consisted of long columns of a clear white light, shooting up from
the horizon to the eastward, almost to the zenith, and spreading
gradually over the whole southern parts of the sky. These columns even
sometimes bent sideways at their upper extremity; and, although in most
respects similar to the northern lights, (the =aurora borealis= of our
hemisphere,) yet differed from them in being always of a whitish color;
whereas ours assume various tints, especially those of a fiery and
purple hue. The stars were sometimes hidden by, and sometimes faintly to
be seen through the substance of these southern lights, =aurora
australis=. The sky was generally clear when they appeared, and the air
sharp and cold, the mercury in the thermometer standing at the
freezing-point; the ship being then in fifty-eight degrees south.” On
six different nights of the following month (March) the same phenomenon
was observed.