Ellsworth American. [volume] (Ellsworth, Me.) 1855-current, 1869-06-10
Theorys Of Auroras.

4 ne isiSuN ~ ~ ~
| frequently seen near the horizon. bear
ing some resemblance TO the morning
twilight, whence 1t has received the
name of aurora. In the northern hem
ispherc it Is usually termed aurora
borcalis," because it is chiefly seen in
the north. A similar phenomenon is
also seen in the southern hemisphere,
where il is called aurora Australis,"
Each Of them may. with greater pro-
prietv. be called .Anrora Polaris" or
Polar Light They exhibit an endless
variety of appearance. In the United
States an aurora is uniformly preceded
by hazy or slaty appearance of the
sky, particularly in the neighborhood
of the northern horizon. W hen the
auroral display commences, this hazy
portion OF the sky assumes the form Of
dark bank or segment Of circle in
the north, rising ordinarily 10 the
height of from FIVE 10 ten degrees.
This dark segment is not a cloud, for
the stars are seen through il as through
smoky atmosphere. with little dimlnn-
iion OF brilIiancy This dark bank is
simply dense haze. and it appears
darker from the contrast with the lum-
inous are which rests upon it, la high
northern attitudes, when the aurora
covers the entire heavens, the whole
sky seems filed with dense haze
anl in still higher latitudes, where the
aurora is sometimes seen in the south.
TIN, dark segment is observed resting
on the southern horizon and bordered
by the auroral light.
Auroras are sometimes observed
simu ltaneously over large portions of
the globe. The aurora Of August 2s,
1883, was seen throughout more than
l4a degfees of longitude, from Eastern
Europe to California and from Jamal-
ca on the south u an unknown dis
tance in British America on the north.
The aurora of September =, 1893, was
seen at the Sandwich Islands II was
seen throughout the whole Of North
America and Europe and the disturb
ance of the magnetic needle indicated
its presence throughout all Northern
Asia, although the sky was overcast,
so that mt many places it could not be
seen. An aurora was seen at the same
time in south America and New llol-
land. The aurora, Of September -.
ISIS, were almost equally extensive.
The height of large number Of an
roras has been computed. and the aver.
age result for the upper limit of the
streamers is 40 miles. From null
titude of observations il j. ccnclu ded
that the aurora seldom appears AT an
elevation less than about 10 miles
above the earth's surface, and that 1t
frequently extends upward To an eieva-
ton Of 500 miles. Auroral arches haN-
ing well-detined border are generally
less than 100 miles III height.
Auroras are very unequalIy dl>tri-
buted over the earths surface. They
occur most frequently IN the higher
latitudcs. and are almost unknown
within the tropics. At Havana. IN
latitude % degrees. but SIX auroras
have been recorded within hundred
wears. and south Of Havana auroras
are still more untrequent. A. We
ravcl northwafd from Cuba, auroras
increase in frequency and brilhancy
| they rise higher IN the heavens, anu
| ottencr ascend to the ZENITH. Nen
the parallel Of 40 degrees We find on
an average only ten auroras annually
Near the parallel of ~ degrees the
average lumber is twenty annually :;
near 45 degrees The number is forty !;
and near the parellel of 30 degrees it
amounts To eighty annually. Between
this point and the parallel Of " de-
grses auroras. during the winter, are
seen almost every night. They ap
pear high III the heavens and q, Of
ten to the south as the north. La re-
gions further north they are seldom
seen except in the south, and from this
point they diminish i'll frequency and
brillancy a. we advance toward the
pole. Beyond latitude 81 degrees the
average number OF auroras is reduced
to forty annually. Beyond latitude 81
degrees it is reduced To twenty: and
near latitude 7S degrees it Is reduced
To ten annually.
Auroral exhibitions take place in
the upper regions OF the atmosphere
since they partake of the earth's ro
tation. All the celestial bodies have
an apparent motion from east to west
arising from the rotation of the earth
but bosiie. belonging TO the earth. in
clading the atmosphere and the clouds
which float in it, partake of the earth
rotation. so that their relative position
is not affected BY it. The same il
true Of auroral exhibitions. When
ever an auroral corona is formed.
maintains sensibly the same position
in the heavens during the whole pcrio'
of its continuance, although the star
meanwhile revolve at the rate Of Is de
Q grees per hour.
Q The grosser part of the earth's u
. mosphere is limited to = moderass dii
i lance from the earth. At the heigt