The morning news. [volume] (Savannah, Ga.) 1887-1900, 1897-07-04
PHENOMENA OF THE AURORA.

Still q Puzzle to Scientific Observers.
DR.. Henry S. Williams, in Harper's Mag
azine.
If fre-balls were thought miraculous
and portentous in days of yore what in
depreciation must needs have been put
upon that vastly more picturesque phe-
nomena, the aurora? Through all the
city," says the book of Maccabees, "for
the space of almost forty days, there were
seen horsemen running in the air. in
cloth of gold, armed with lances, like a
band of soldiers; and troops of horsemen
in array encountering and running one
against another. with shaking of shields
and multitude of pixies, and drawing of
swords, and casting of darts, and glitter
ing of golden ornaments and harness"
Dire omens these; and hardly less ominous
the aurora seemed to all succeeding gen.
erations that observed 1t down till Will
into the eighteenth century-as witness
the popular excitement in England in 17l6
over the brilliant aurora of that ear,
which became famous through Us
description.
But after 1852, when Franklin ION
ed the lightning, all spectacular nleteors
ena, the aurora among the rest. Frank
lin explained the aurora-Which was seen
commonly enough in the eighteenth CEN
fury, though only recorded once in the
seventeenth-as due to the accumulation
of electricity on the surface of polar
SHOWS and its discharge to the equator
through the upper atmosphere. Erasmus
Darwin suggested 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 hight of the au-
rora, estimating it at about 100 miles,
thought the phenomenon due to magnet
ism acting on ferruginous particles 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
studied the aurora, but the scientific
grasp has found 1t as elusive in fact as it
seems to casual observation, and its ex-
act nature is as undetermined to-day as
1t was hundred years ago. There mas
been no dearth of theories concerning it,
however Blot, who studied it in the Shet-
land Islands in 1917, thought it due to cleo
trifed feruginous dust, the origin of which
he ascribed to Icelandic volcanoes. Much
more recently the idea of ferruginous par
ticles has been revived, their presence be-
ing ascribed, not to volcanoes, but to the
meteorites constantly being dissipated in
the upper atmosphere. Ferruginous dust,
presumably of such origin, has been found
on the polar SHOWS, as well as on the
SHOWS of mountain tops, but whether 1t
could produce the phenomena of auroras
is at least an open question. The prevail
ing theory of to-day is that the aurora is
due to a current of electricity generated
at the equator. and passing through upper
regions of space 20 enter the earth at the
magnetic poles-stmply 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 support to
the long-standing supposition that the au-
rora is of electrical origin. but the subject
still awaits complete elucidation. For once
even that mystery-solver, the spectre
scope, has been baffled, 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, IL Is true,
but this is OF little aid, for the zodiacal
light, though thought by some astrono-
mers to be due TO meteor swarms about
the sun, is held TO be, on the whole, as
mysterious as the aurora itself.
Whatever the exact nature of the aurora
Il has long been known TO be intimately
associated with the phenomena of terres-
trial magnetism. Whenever a brilliant au-
rora is visible, the world is sure to be Wis
tied with what Humboldt called a magnet
10 storm-a storm" which manifests It.
self TO human senses in no way whatso-
ever except by detecting the magnetic
needle and conjuring with the electric
wire. Such magnetic storms are curiously
associated also with spots on the sun-just
how no one has explained, though the fact
itself is unquestoned. Sun-spots, too.
seem directly linked with auroras each
OF these phonemena passing through pc
RODS Of greatest and least frequency in
corresponding cycles Of about II years
duration.