274 
NWATOURE 
[Fuly 23, 1885 
THE AURORA? 
I. 
R. TROMHOLT has rendered a great service to 
science by the travels and observations recorded 
in these volumes ; indeed, it would not perhaps be going 
too far to say that we have here, brought before us in the 
most interesting manner, one of the best organised 
attempts to study the aurora that has been made for 
many years, the credit for which must be given to the 
organisers of the International Polar Research Expedition 
of 1882-83. Mr. Tromholt’s duty was to observe all 
auroral phenomena in the Lapp settlement of Kouto- 
kzeino, and above and beyond this to observe in such a 
way that, in combination with other observations arranged 
for at the Norwegian station at Bossekop in Finmarken 
and the Finnish one at Sodankyla in the centre of Finland, 
certain conclusions might be arrived at regarding the 
height at which the various displays take place. 
The results, however, recorded in these volumes are by 
no means limited to the height of the aurora. The constant 
study afforded to Mr. Tromholt and his con/fréres at the | 
other stations of one of the most awe-inspiring phenomena 
which it is given to man to witness have permitted 
generalisations to be reached and hypotheses to be 
broached of the greatest scientific interest ; and this must 
be our excuse for dwelling on the general results of this 
recent work in the present article, including also a notice 
of those of Nordenskjéld in the Vega Expedition 1878-79. 
Let us begin by considering the general phenomenon 
of an aurora as seen in Northern Europe. Mr. Tromholt 
gives the following general description of a great 
display :— : 
“Tt is a lovely evening in spring or autumn. The light 
is fast fading away in the west, and one star after another 
comes out of the azuresky. Suddenly a peculiar vibrating 
luminosity appears high up in N.E., now with a soft 
purple tinge, and now diffused with long narrow streamers, 
reaching to the Pole star, or beyond. It is wafted to and 
fro like a curtain before a light breeze, and its light 
becomes more and more intense as Night spreads her 
dark veil over the sky. Suddenly the luminous cloud is 
furrowed from one end to another by a bunch of streamers, | 
the lower, emerald-green ends of which rest almost on 
the horizon, while the upper diffuse points, which flame | 
with a purple lustre, reach right up to the Zenith, 
Streamer oscillates by streamer, more and more follow, 
and, with a rapidity almost startling, the aurora expands 
westwards, and shortly after the whole northern sky is a 
bath of fire. Like a curtain woven of light and colour 
the streamers hang fairy-like in the air; here and there 
they form large graceful folds and sway to and fro in 
wonderful beauty, as if the wind played on the radiating 
drapery. Red and green play alternately in the lower 
border of the curtain. For a few minutes longer the 
marvellous play of light lasts, the varying forms, colours, 
and motions charm the mind as much as the eye—the 
forces are then exhausted, the lovely picture grows more 
and more obscure, and the forms are dissolved into large 
soft clouds of light, covering nearly the entire northern 
half of the heavens. 
“Down by the horizon there is still, however, great 
activity, as here a couple of arcs have formed, the con- 
stant-changing play of which enchains the spectator 
during the evtyacte between the past and coming scene 
of the sublime drama which Nature performs on the great 
stage of heaven : now faint, then strong, soon symmetrical, 
soon serpent-like, in one moment split into three or four 
arcs, and again gathering into one, now woven with all 
the lovely colours of the rainbow, now throwing forth rays 
and resembling the ornamental pipes in an enormous 
organ—such is the spectacle I gaze on. 
* “Under the Rays of the Aurora Borealis.” By S. Tromholt. Edited 
by Carl Siewers. (London : Sampson Low and Co., 1885.) 
“At this moment a narrow, white streamer suddenly 
leaps up from the horizon in the east, a similar one 
appears in the west ; they both grow rapidly in length, 
their points meet, and a grand arc spans the sky right 
above the observer. Simultaneously two long and broad 
sheafs of streamers, woven of white and red filaments, 
develop at the bases of the arc. The luminosities on the 
northern sky again catch fire, and soon after the whole 
heavens in the north is again ablaze. Quicker and 
quicker the motions become and intenser the colours, 
higher and higher the streamers travel, the points ap- 
proaching the great arc, which is moving slowly south- 
wards. Other groups of streamers form at greater alti- 
tudes, in east and west, and the luminous masses cover 
more and more of the sky. Now a number of white 
bands suddenly appear overhead, shoot right across the 
sky from east to west, and then rush southwards, and 
vanish. By this time the luminous masses have crossed 
the zenith, the points of the streamers meet in a spot high 
in the southern sky, while in the east and west the sphere 
of the streamers moves gradually southwards. A wonder- 
ful spectacle is now presented to view. In every direction 
the whole sky is covered with bunches of streamers, all of 
which point to this spot—the magnetic zenith—and 
transform the vault of heaven into one gigantic lustrous 
cupola, the beauty of which no pen can describe, no 
brush depict. All the marvellous zwances of colour of 
the rainbow contribute to ornament the vault; here is 
the tender green of the emerald, the grand purple of the 
ruby, and the charming blue of the sapphire, all blended 
together in a thousand shades. Here gamble a flock 
of yellow-green flames, and there mighty pillars rise as if 
to support the luminous vault, while yonder the sky is 
covered with a transparent drapery shot with red, behind 
which dazzling white streamers stand forth. It is the 
auroral corona. 
“A lovelier spectacle is not given the human eye to 
behold ; he who has not seen it cannot form an idea of 
its magnificence—it defies description. 
“For a moment the glorious, luminous vault remains 
thus in majestic beauty, then the supporting arches 
tremble for a moment, and fall, the faint light-clouds 
remaining in the southern sky vanish, and the aurora 
recedes to the northern sky. Here the streaming and 
play of colour continues for a while in manifold variation ; 
but the area of the luminosity grows smaller and smaller, 
and moves steadily downwards to the horizon. A remark- 
able phenomenon now occurs in the soft luminosities, 
which still stand high in the northern sky: they appear 
to leap upwards with the rapidity of lightning, and then 
disappear ; in several other spots similar clouds come 
forward and chase each other over the sky. The eye is 
hardly able to follow their strange gambols. Again the 
streamers grow in length, the light-clouds cease their 
play, and once more the streamers approach the zenith. 
But now they do not cross it ; they remain in majestic 
rest for a few seconds, and then slowly disappear. 
“Hour after hour this marvellous display continues in 
the northern sky, now stronger now fainter, and often it 
does not cease before the first streaks of dawn appear in 
the east.” 
It must not be imagined, however, that the displays 
generally are of this brilliancy ; aurora are generally 
much weaker, and in these cases the phenomena are 
different. Here is a general description of a weak 
aurora :— 
“The sun set some hours ago. The purple glow in the 
west has disappeared, myriads of stars stud the dark 
canopy. Far down on the horizon, in north-west and 
north, lies a faint vague cloud of light, upwards and 
downwards fading into the sky . . . : 
“Soon after, tiny spots of intense light begin to appear 
in the luminous cloud, while at times the entire oscillating 
luminosity disappears from the sky. But still the light is 
