Yorkville enquirer. [volume] (Yorkville, S.C.) 1855-2006, 1869-06-24
THEORIES OF, AURORAs,


seen near the horizon, bearing some resemblance
to the morning twilight, whence it has received
the name Of aurora. In the Northern Hemisphere
it is usually termed "Aurora Borealis," because it
is chiefly seen in the North. A similar phenome-
ma is also seen in the Southern Hemisphere, where
it is called "Aurora Australis" Each Of them
may, with greater propriety, be called Aurora
Polaris, or Polar Light. They exhibit an end
less variety of appearances In the United States
an aurora is uniformly preceded by hazy or slaty
appearance of the sky, particularly in the neigh
berhood Of the Northern horizon. When the au-
roral display commences, this haiy portion Of the
sky assumes the form of dark bank or segment
of circle in the North, rising ordinarily to the
height of from five to ten degrees. This dark seq
ment is not cloud for the stars are seen through
it as through smoky atmosphere, with little dim
mutton of brilliancy. This dark bank is simply a
dense haze, and it appears darker from the contrast
with the luminous arc which rests upon it In
high Northern latitudes when the aurora covers
the entire heavens, the whole sky seems filed
with q dense haze; and in still higher laitudes,
where the aurora is sometimes seen in the South,
this dark segment is observed resting on the South
ern horizon and bordered by the auroral light. =
Auroras are sometimes observed simultaneously
over large portions Of the globe. The aurora Of
August %, 1859, was seen throughout more than
40 degrees of longitude, from Eastern Europe to
California; and from Jamaica on the South to an
unknown distance in British America on the North.
The aurora Of September 2, 1859, was seen at the
Sandwich Islands; it was seen throughout the
whole of North America and Europe; and the dis
turbance Of the magnetic needle indicated its pres
ence throughout all Northern Asia, although the
sky was overcast, so that at many places it could
not be seen. An aurora was seen at the same
time in South America and New Holland. The
auroras of September 25, 1s41, and November
II, 1S4S, were almost equally extensive.
The height of large number Of auroras has
been computed, and the average result for the up
per limit of the streamers is $50 miles. From
multitude of observations it is concluded that the
aurora seldom appears at an elevation less than As
miles above the earth's surface, and that it fire.
quently extends upward to an elevation Of 500
miles, Auroral arches having well-deGned bor-
der are generally less than 100 miles in height.
Auroras are very unequally distributed over the
earth's surface. They occur most frequently in
the higher latitudes, and are almost unknown
within the tropics. At Havana in latitude % de-
grees, but six auroras have been recorded within
hundred years, and South of Havana auroras are
still more unfrequent. AS we travel Northward
from Cuba, auroras increase in frequency and bril-
Iancy; they rise higher in the heavens and often
er ascend to the zenith. Near the parallel of 40
degrees we find on an average only ten auroras an
nually. Near the parallel Of AZ degrees the aver
age number is twenty annually; near As degrees
the number is forty: and near the parallel OF so
degrees it amounts to eighty annually. Between
this point and tho parallel of 81 degrees, auroras,
during the winter, are seen almost every night.
They appear high in the heavens and as often to
the South as to the North. In regions further
North they are seldom seen except in the South,
and from this point they dimish in frequency and
brilancy as we advance towards the pole. Beyond
latitude 62 degrees the average number of auroras
is reduced to forty annually. Beyond latitude 81
degrees it is reduced to twenty; and near latitude
IS degrees it is reduced to ten annually.
Auroral exhibitions take place in the upper re-
gions of the atmosphere, 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 atmosphere and the clouds
which float in it, parake of the earths rotation, SO
that their relative position is not affected by it.
The same is true of auroral exhibitions. Whenever
an auroral corona is formed, it maintains sensbly
the same position in the heavens during the whole
period of its continuance although the stars mean
while revolve at the rate of Is degrees per hour.
The grosser part of the earth's atmosphere isl