The Universalist. [volume] (Chicago [Ill.]) 1884-1897, 1897-06-26
WHAT CAUSES THE AURORA
BOREALIS.

IL fire-balls were thought miraculous
and portentous in days of yore, what in
depreciation must needs have been put
upon that vastly more picturesque phe-
nomenon. the aurora? Through all the
the city" says the Book OF Maccabeee,
"for the space of almost forty daye, there
we're seen horsemen running in the air,
in cloth of gold, armed with lances, like
a band OF soldiers: and troops Of horse
men 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 glittering of golden ornaments and
harness." Dire omens these; and hard
ly less ominous the aurora seemed to all
succeeding generations that observed it
down till we'll into the eighteenth Gen.
tury-as witness the popular excitement
in England in 1716 over the brilliant
aurora of that year, which became ia.
nous through Halley's description.
But after 1852, when Franklin de-
tAIOuOo bu0 5pOCtoCuidI
meteors came to be regarded as natural
phenomena, the aurora among the rest.
Franklin explained the aurora-which
was seen commonly enough in the eigh-
tenth century, though only recorded
once in the seventeenth-as due to the
accumulation of electricity on the sur
tace of polar SHOWS, and its discharge to
the equator through the upper atmus-
phere. Erasmus Darwin suggested that
the luminosity might be due to the igni-
ton of hydrogen. which was supposed
by many philosophers to form the upper
atmosphere. Dalton, who first meas.
ured the height of the aurora, estimat-
ing it at about one hundred miles,
thought the phenomenon due to mag ct.
ism acting On ferruginous particles in
the air, and his explanation was perhapc
the most popular one at the beginning
Of the century.
Since then multitude of observers
have studied the aurora. but the scien-
tific grasp has found it as elusive in fact
as it seems to casual observation, and
its exact nature is as undetermined to-
day as it was hundred years ago. There
has been no death of theories concern
ing it, however. Blot, who studied it in
the Shetland Islands in 1917, thought it
due to electrified ferruginous dust, the
origin of which he ascribed to Icelandic
volcanoes. Much more recently the idea
of ferruginous particles has been re-
vived. their presence being ascribed not
to volcanoes. but to the meteorites con.
stantly being dissipated in the upper
atmosphere. Ferruginous dust, presum-
ably of such origin, has been found on
the polar SHOWS, as well as on the SHOWS
of mountain-tops, but whether it could
produce the phenomena of auroras is at
least an open question. The prevailing
theory Of today is that the aurora lie due
to a current of electricity generated at
the equator, and passing through upper
regions 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 vacuum bulb by the
passage Of electricity lends support to
the long standing supposition that the
aurora is of electrical origin, but the
subject still awaits complete elucida-
ton. For once even that mystery solver
the spectroscope has been baffled. for the
line it Sits from the aurora is not
matched by that of any recognized SUBJ
stance. A like line is found in the 20
diacal light, it is true. but this is of little
aid, for the zodiacal light, though
thought by some astronomers 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 au-
rora, it has long been known to be init
mately associated with the phenomena
of terrestrial magnetism. Whenever a
brilliant aurora is visible, the world is
sure to be visited with what Humboldt
called magnetic storm-a "storm"
which manifests itself to human senses,
in no way Whatsoever except by defect
ing the magnetic needle and conjuring
with the electric wire. Such magnetic
storms are curiously associated also
with spots on the sun just now no one
has explained, though the fact itself is
unxuestioned. Sun-spots. too, seem d.
rectly linked with auroras, each of these
phenomena passing through periods of
greatest and least frequency in CORES
ponding cycles of about eleven years
DURATION Henry Smith Williams. NJ
d., an Hdrper's Magazine for June
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