The Black Hills union. [volume] (Rapid City, Pennington County, Dakota [S.D.]) 1889-1904, 1897-08-06
CAUSES AURORA BoREALls.
Exact Nature of the Phenomenon Still q
Mystery.

Exact Nature Of the henomen Still .
Mystery.
If fire-halls we're thought miraculous
and portentous in days Of yore, what
Interpretation must needs have been
put upon that vastly more picturesque
phenomenon, the aurora? asks Har-
per's Magazine. Through all the
city," says the Book of Maccabees, "for
the space IT almost forty days, there
We're seen horsemen running in the
air, In cloth of gold, armed with lances,
like a band of soldiers; and troops Of
horsemen in array e"ncountering and
running n against another, with
shaking Of shields and multitude of
pixies, and drawing of swords and cast
ing OF darts, and glittering of golden
ornaments and harness." Dire omens
these; and hardly less ominous the
aurora seemed to all succeeding gen
erations that observed it down till we'll
into the eighteenth century-as wit
ness the popular excitement Ia Eng
land IN l7l6 over the brilliant aurora
or that year, which became famous
through Halley's description. But af-
ter 1852, when Franklin dethroned the
lightning, all spectacular meteors came
to be regarded as natural phenomena,
the aurora among the rest. Franklin
explained the aurOra-which was seen
commonly enough in the eighteenth
century, though only recorded once
Ii the seventeenth-as due to the &C
emulation of electricity on the sur
faee of polar SHOWS and it's discharge
TO the equator through the upper at
nosphere. Erasmus Darwin suggest
ed that the luminosity might be due to
the ignition Of hydrogen, which was
supposed by many philosophers to
form the upper atmosphere. Dalton,
who first measured the height of the
aurora, estimating it al about 100
miles, thought the phenomenon due to
magnetism acting on ferruginous par
ticles in the air, and his explanation
was perhaps the most popular one at
the beginning Of the century. Since
then a multitude of observers have stu
died the aurora, but the scientific grasp
mas found it as elusive in fact as it
seems to casual observation, and it's
exact nature is as undetermined to-day
as 1t was 100 years ago. There has been
no dearth of theories concerning it,
oWever Blot, who studied it in the
shetland islands in 1917, thought it
due to electrified ferruginous dust. the
origin Of which he ascribed to Ice
landic volcanoes. Much. more recent
~ the idea Of ferruginous particles has
been revived, their presence being as
crlbed not to volcanoes but to the me-
teorltes constantly being dissipated in
the upper atmosphere. Ferruginous
dust, presumably of such origin. has
been found on the polar SHOWS, as we'll
DIS on the SHOWS OF mountain tops, but
whether it could produce the phenom-
ena OF auroras is at least an open uues-
tlon. The prevailing theory of to-day
IS that the aurora is due to a current
OF electricity generated at the euua-
tor, and passing through upper re-
gions of space. to enter the earth at
the magnetic poles-simply reversing
the course which Franklin assumed.
The similarity of the auroral light to
that generated in a vacuum bulb by
the passage Of electricity lends sup
port to the long-standing supposition
that the aurora is of electrical origin
out the subject still awaits complete
calculation. For once even that mys-
.~ery-solVer, the spectroscope, has been
baf1ed, for the line it Sits from the
aurora is not matched by that of any
recognized substance. A like line is
found in the zodiacal light, it is true.
out this is of little aid, for the zodiacal
llget, though thought by some astro-
nomers to be due to meteor swarms
o the sun, is held to be, on the
WHOLE, as mysterious as the aurora it.
self.