Prof. Hansteen on the Aurora Borealis. ' 91 
1. When the aurora borealis is vivid, the horizontal magnet 
becomes restless, varies in a few minutes from three, four, to five 
degrees from its ordinary place, and sometimes gets into a qui- 
vering motion, which shews, that, at that time, the magnetic 
powers of the earth are in a state of great agitation. % A short 
time before the aurora borealis appears, the intensity of the mag- 
netism of the earth is apt to rise to an uncommon height ; but 
so soon as the aurora borealis begins, in proportion as its force 
increases, the intensity of the magnetism of the earth decreases, 
recovering its former strength by degrees, often not till the end 
of twenty-four hours. These changes are sometimes so sudden, 
that I once observed a considerable difference in the space of 
from two to three minutes. (The Professor here details an ex- 
periment made with a fine magnetic needle, suspended by the 
thread of a silk worm. He counted its vibrations to the amount 
of 360 ; and dividing this number into equal portions, and com- 
paring by a chronometer the time occupied by each portion, he 
found a difference in the number of vibrations performed in the 
same time, far exceeding any thing which could arise from the 
inaccuracy of the observation, proving a difierence during the 
time of the experiment in the intensity of the magnetic force.) 
From this, he says, it seems to follow, that the polar lights are 
the effect of an uncommonly high magnetic intensity, which in- 
tensity lets itself off, as it were, by the polar lights, and thus 
sinks under its common strength. 3. During the time of a 
powerful display of the aurora borealis. Mallet and others have 
found no uncommon strength of electricity in the air, which 
seem to disprove the hypothesis of Franklin. 4. The Reverend Mr 
Steenbuck, who was the editor, and, in a great measure, the au- 
thor of the Description of the Kingdom of Norway., published 
under the name of Jessen, and who was himself born in the pro- 
vince of Trondheim, relates, concerning the arch of the aurora 
borealis, that, according to the accounts of old people, this arch 
was wont to appear lower on the horizon in Nordland, and near- 
er to the true north ; that, since these times, it has risen higher 
in the sky, and removed from the meridian towards the west. 
This agrees entirely with the change of place of the North 
American magnetic pole, by which it lies some nearer to us, 
and lies in a plane which forms a larger angle with the meri- 
