unaltered in position. When the sky was not clouded over and the faint
light of the aurora was not dimmed by the rays of the sun or the full
moon, these arcs commonly began to show themselves between eight and
nine o'clock P.M., and were then seen without interruption during
midwinter till six, and farther on in the year to three o'clock in
the morning. It follows from this that the aurora even during a minimum
year is a permanent natural phenomenon. The nearly unalterable position
of the arcs has further rendered possible a number of measurements of
its height, extent, and position from which I believe I may draw the
following inferences that our globe even during a minimum aurora year is
adorned with an almost constant, single, double, or multiple luminous
crown, whose inner edge is situated at a height of about 200 kilometres
or 0.03 radius of the earth above its surface, whose centre, "the
aurora-pole," lies somewhat under the earth's surface, a little north of
the magnetic-pole, and which, with a diameter of 2,000 kilometres or 0.3
radius of the earth, extends in a plane perpendicular to the radius of
the earth, which touches the centre of the circle.

[Illustration: THE COMMON AURORA ARC AT THE "VEGA'S" WINTER
QUARTERS. ]

[Illustration: AURORA AT THE "VEGA'S" WINTERER QUARTERS, 3RD MARCH
1879, AT 9 P.M. ]

[Illustration: DOUBLE AURORA ARCS SEEN 20TH MARCH 1879,
AT 9.30 P.M. ]

[Illustration: ELLIPTIC AURORA SEEN 21ST MARCH, 1879, AT 2.15 A.M. ]

[Illustration: ELLIPTIC AURORA SEEN 21ST MARCH, 1879, AT 3 A.M. ]

I have named this luminous crown _the aurora glory_ on account of
its form and its resemblance to the crown of rays round the head of
a saint. It stands in the same relation to the ray and drapery
auroras of Scandinavia as the trade and monsoon winds in the south
to the irregular winds and storms of the north. The light of the
crown itself is never distributed into rays, but resembles the light
which passes through obscured glass. When the aurora is stronger,
the extent of the light-crown is altered double or multiple arcs are
seen, generally lying in about the same plane and with a common
centre, and rays are cast between the different arcs. Arcs are
seldom seen which lie irregularly to or cross each other.

The area in which the common arc is visible is bounded by two circles
drawn upon the earth's surface, with the aurora-pole for a centre and
radii of 8 deg. and 28 deg. measured on the circum