The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1869-06-03
miscellaneous.
Theorys of Auroras.

From an article By Prof Loomi., of
Yale College, in Ha,pcr's Mrgaaiae for
June, We make the following extracts
The Polar Light is a light which is
is frequently seen ncgr the horizon,
bearing some resemblance to the
morning twilight, whence it has
received the name Of aurora. In the
northern hemisphere 1t is usually term
ed aurora borealis,' because it is chiefly
seen IN the north. A similar pheuom.
euon is also seen in the southern hemls
phcrc, where it is called aurora Aus.
trails Each Of them may, with greater
propricty, be called Aurora polaris.
or F1iir Liyht They exhibit an end.
less variety Of appearances. In the
United States an aurora is uniformly
proceeded by hazy or slaty appearance
Of the sky, particularly in the ucishbor.
hood of the northern horizon When
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 to
the height Of from five to ten degrees.
This dark segment is not cloud, for
the stars are seen through it as through
a smoky atmosphere, with little diminu.
tion OF brilliancy. This dark bank is
simply dense haze, and it appears
darker from the contrast with the lumi.
nous arc which rests upon it. In high
northern attitudes, when the aurora
covers the entire heavens. the whole
sky seems filed with dense haze and
in still higher latitudcs, where the
aurora is sometimes seen in tho south,
this dark segment is observed resting
on the southern horizon aud bordered
by the auroral light.
Auroras are sometimes observed ST.
mutaneously over large portions Of the
globe, The aurora ot August 2S, 1859,
was seen throughout more than 40
degrees of longitude, from Eastern Eu.
rope 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 disturbance of the
magnetic needle indicated its presence
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 10 South
America and New Holland. The auroras
Of September %, 1871, and November
II, 1913, were almost equally extensive.
The height Of large number of au-
roras has been computed, and the aver.
arge result for the upper limit of the
streamers is 400 miles. From multi
tude of observations it is concluded that
the aurora seldom appears at an eleya-
tion less than about As miles above the
carths surface, aud that it frequently
extends upward to an elevation of 800
miles. Auroral arches having q well.
defined border are generally less than
100 miles iii height.
Auroras are very unequally distribu.
ted over the earth's surface. They oc-
cur most frequently in the higher lati-
tudes, and are almost unknown within
the tropics. At Havana, in latitude %
degrees, but six auroras have been re-
corded within hundred years, and
south of Havana auroras are still more
uufrequent As we travel northward
from Cuba, auroras increase 10 frequency
aud brilliancy; they rise higher in the
heavens, and oitener ascend to the
zenith. Near tho parallelof 40 degrees
we find on 40 average only ten auroras
annually Near the parallel Of AZ de-
gross the average number is twenty
annually; near 45 degrees the number
is forty; and near the parallel Of 80
degrees it amounts to eighty annually
Between this point.a and the parallel Of
SO degrees auroras, during the winter,
are seen almost every night Thep ap-
pear high ID the heavens, aud asf often
to the south as the north In regions
farther north they are seldom seen exl
cept 10 the south. aud from this Joint
they diminish in frequency aud bril-
liaDcy as we advance toward the pole.
Beyond latitude G2 degrees the average
pumber Of auroras is reduced TO forty
annually. Beyond latitude 67 degrees
It is reduced to twenty; aud near lati.
tude rs 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 rotation.