Nashville union and American. [volume] (Nashville, Tenn.) 1868-1875, 1869-05-30
THE NORTHERN LIGHTS.
Theories OF the Aurora ROrealis-rhe
Height or AuRoras and where they
Most Frequently Appear.

. | the June number of Harper's Ma.
azfne, on the Aurora Borealis, frol
? which we extract as follows:
The Polar Light is light whic
is frequently seen near the horizon
bearing some resemblance to tn
morning twilight, whence it has re
eeived the name of aurora. In tn
northern hemisphere it is usual.
termed Aurora Borealis because
is chiefly seen in the north. A sim
| liar phenomenon is also seen IN thu
southern hemisphere, where 1T i:
called Aurora Australis. Each o.
them may with, greater propriety
be called Aurora Polaris, or Polar
Light. They exhibit an endless
variety of appearances. In the
| United States an aurora is uniformly
preceded by a bazy or slaty appear
| ance of the sky, particularly In the
neighborhood of the northern hor-
lion. When the auroral display
commences, this hay portion OF the
sky assumes the form OF a dark
bank or segment of a circle in the
north, rising ordinarily to the height
of from five to ten degrees. This
dark segment is not a cloud, for
the stars are seen through it as
through smoky atmosphere, with
little diminution of brilliancy. This
dark bank is simply dense haze,
and it appears darker from the
contrast with the luminous arc
which rests upon it. In high
northern ATTITUDES, when the aurora
covers the entire heavens, the whole
sky seems filed with q dense haze
and in still higher ATTITUDES, where
the aurora is sometimes seen in the
south, this dark segment is OBJ
served resting on the southern hor-
lion and bordered by the auroral
light.
Auroras are sometimes observed
simultaneously over large portions
of the globe. The aurora of Au.
gust, %, 1859, was seen through
out more than 140 degrees of lOngi
tude, from Eastern Europe to Cali
fornia and from Jamaica on the
South to an unknown distance in
British America on the North. The
aurora of September 3, 1859, was
seen at the Sandwich Islands; it
was seen throughout the whole Of
North America and Europe; and
the disturbance of the magnetic
needle indicated its presence
throughout all Northern Asia, al
though the sky was overcast so
that at many places it could not be
seen. An aurora was seen ut the
same time in South America and
New Holland. The aurora of Sep
tember %, 1911, and November II,
1858, were almost equally extensive.
The height of large number OF
auroras has been computed, and the
average result for the upper limit
of the streamers is $50 miles.
From a multitude Of observations
it IS concluded that the aurora sell
dom appears at an elevation less
than about forty-fiVe miles above
the earth's surface, and that it fire.
quently extends upward to al. ele-
walton of 500 miles. Aurora arches
having a well-defned border are
generally less than 100 miles in
height.
AurOras are very unequally dis
tributed over the earth's surface
They occur most frequently in the
highest ATTITUDES, and are almost
unknown within the tropics. At
in latitude 90 degrees, but
six auroras have been recorded
within a hundred years, and south
of Havana auroras are still more
As we travel north
ward from Cuba, auroras increase |
in frequency and brilliancy; they
rise higher in the heavens, and
Oftener ascend to the zenith. Near |
the parallel of 40 degrees We find on
an average only ten auroras annu-
ally. Near the parallel of AZ de-
grees the average number is twenty |
annually; near 45 degrees the num-
Der is forty; and near the parallel
Of fifty degrees it amounts to eighty /
annually. Between this point and
the parallel of 60 degrees auroras /
during the winter are seen almost
every night. They appear high in
The heavens, and as often to the |
south as the north. In regions fur
Their north they are seldom seen
except in the south, and from this
point they diminish in frequency |
and brilliancy as we advance toward
the pole. Beyond latitude G2 de-
grees the average number of aurO-
ras is reduced to forty annually.
Beyond latitude 81 degrees it is re
duced to twenty; and near latitude
78 degrees it is reduced to ten an
nually.
Auroral exhibitions take place in
the upper regions of the atmOs-
phere, since they partake of the |
earth's rotation. All the celestial
bodies have an apparent motion
from east to west, arising from the
rotation of the earth but bodies
belonging to the earth, including
the atmOspheres and the clouds
which float in it, partake of the
earth's rotation, so that their rela
tive position is not affected by it.
The same is true of auroral exhibi-
tions. Whenever the auroral cOro-
ma is formed, it maintains sensibly
the same position in the heavens
during the whole period of its con-
tinuance, although the stars mean
while revolve at the rate of fifteen
degrees per hour.
The grosser part of the earth's
atmosphere is limited TO moderate
distance from the earth. AT the
height of q little over four miles, the
density of the air is only one-half
what it is at the earth's surface. At
the height of fifty miles the atmos-
phere is well-nigh inappreciable in
its effect upon twilight. The phenO-
mena of lunar eclipses indicate an
appreciable atmosphere at the