The Plymouth weekly Democrat. (Plymouth, Ind.) 1860-1869, 1869-06-10
Theories of the Aurora BoreaIis.

| THE Polar Light is light which is fre.
! quently seen near the hOriZ N, bearing
| some resem blsnce to the morning twilight,
whence 1t has received the name Of Au-
rora. In the northern hemisphere it is
usually termed Aurora BOrealis" be-
cause 1t IS chiefly seen in the north A
similar phenomenon is also seen in the
southern hemisphere, where it is called
aurora Australis." Each of them NAV.
with greater prOprietv, be called Aurora
Polaris," or Polar Light, They exhibit an
endle-s variety of appearance. In the
United States an aurora is uniformly pre-
ceded by hazy or slaty appearance of the
sky, particularly in the neighbOrhood of
the northern horizon. When the aurOral
display commences, this hazy 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 il as
through smoky atmosphere, with little
diminuion 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 COW
ers the entire heavens, the whole skv
seems filled with dense haze and in still
higher latitudes, where the aurora is some
times seen in the south, this dark segment
| is observed resting on the southern hori-
zon and bOrdered by the auroral light.
Auroras are sometimes observed simulta-
neously over large portions of the globe.
The aurora Of August %, 1859, was seen
throughout more than 40 degrees of
longitude, from Eastern Europe To Cali
fornia; and from Jamaica on the south to
an unknown distance III British America
on the north. The aurora of September
2, 1859 was seen at the Sandwich Islands:
1t vas seen throughout the " hole f North
America and Europe and the disturbance
OF the magnetic needle indicated its pres
ence throughout all Northern Asia, al
though 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 p, 1871, and November Il,
1913, were almost equally extensive.
The height OF b large number Of auroras
has been computed, and the average re-
suit Tor the upper limit of the steamers
is 450 miles. From mu titude of obser-
vations it is concluded that the aurora sell
dom appears at an elevation less than
about fOrty-t five miles above the earths
surface, and that it frequently extends up
ward to an elevation of 800 miles Auroral
arches having well-defined border 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 trop-
les. AT Havana, in latitude % degrees,
h,xt l., !
hundred years, and south of Havana
auroras are still more unfrequent AS we
travel northward from Cuba, auroras in
crease in frequency and brilliancy they
rise higher III the heavens, and oftener as
cend to the zenith. Near the parallel of
40 degrees we ind on an average only ten
auroras annually. Near the parallel of
AZ deerees the average number is twenty
annually near 40 degrees the number is
forty and near the parallel Of 80 degrees
it amounts to eighty annually. Between
this point and the parallel of 62 degrees
auror4s, during the winter, are seen al
most every night. They appear high in
the heavens, aud as often to the south as
the north. In regions further north they
are seldom seen except in the south, and
from this point thes diminish in frequen-
cy and brilliancy as We advance toward
the pole Beyond latitu ie 81 degrees the
average number of auroras is reduced to
forty annually. Beyond latitude 81 de-
grees 1t Is reduced 10 twenty; and near
latitude 7S degrees it is reduced to ten an
nually.
Auroral exhibitions take place in the
upper regions of the atmosphere, since
they partake of the earth's rotation. All
the celestial bodies have an apparent mO-
ton from east to west, arising from the rota-
ii N of the earth; but bodies belonging to
the earth, including the atmosphere and The
clouds which float In 1T, partake of the
earth's rotation, that their relative posi-
ton is not affected by it. The same is true
of aurOral exhibitions. Whenever the
aurOral corona is formed, it maintains son
sibly the same position In the heavens
during the whole period of its continuance,
although the stars meanwhile revolve al
the rate of ID degrees per hour
The grosser part of the earth's atmos-
phere Is limited To moderate distance
from the earth. At the height of little
over four miles, the density of the air is
only one half what it is at the earths sur
face. AT the height OF fifty miles the at
mosphere Is well nigh inappreciable in its
effect upon twilight. The phenomena of
lunar eclipses indicate an appreciable at
mOsphere at the height of sixty six miles
The phenomena OF shooting stars indicate
an atmosphere at the height of 200 or 300
miles, while the aurora indicates that the
atmosphere does not entirely cease aJ the
height of 500 miles AurOral exhibitions
take place, therefore, III an atmosphere of
extreme rarity; so rare, indeed, that if,
in experiments with an air-pump, we
could exhaust the air as completely, we
should say that we had obtained 3 perfect
vacuum.
The auroral beams are simply spaces
which are illuminated by the flow of cleo
tricity through the upper regions of the
atmosphere. During the auroras of 1859
these beams were nearly 500 miles in
length, and their lower extremities were
elevated about 40 miles above the earths
surface. Their tops inclined toward the
south about II degrees in the neighbor
hood of New Yoi k, this being he position
which the dipping needle there assumed =
Professor LOoDats, IN Hdrper's Magazine
for June
A FEW days ago, while Judge Barker
was presiding over the Supreme Court at
Lockport, N. Y, juryman WAS absent
from his seat, all the others being occu
pied. A dog, looking for the master. very
~ took ha ~. 4