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Doc. 200.] EXTRACT FROM PROFESSOR CELSIUS. 567
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position of the thread was exactly on 0 of the two graduated
brass -arches. After the thread had been removed the needle
was allowed to swing on its pivot, the whole being covered by
a glass-shade.
I then observed the declination of the needle
towards the west, away from the pole line to be 8° 53’
After the needle had been removed from its
place by means of a key, it stood at 8° 50’
When the compass was handled and replaced
under the thread, the needle indicated . 8° 45’
After being disturbed with a key 8° 47’
When the compass was rubbed and replaced
under the thread . 8° 50’
From all of which results a mean declination
of the needle towards the west for this locality of . 8° 49’
As Assessor Swedenborg has shown how the deviation of
the magnetic needle may be found out a priori for any given
locality, Magister Hiorter245 upon my request has computed
by means of 28 operations the declination of the magnetic
needle for the present time at Upsal according to his theory,
and has obtained 17° 2 }’
A difference from the result obtained by ob
servation of 8° 13;’
He has also computed the declination for
Torneå for April 17, 1736 12° 22’
Which according to my observations is 5° 5’
Thus differing from the real observation 7° 17’
From this it is made sufficiently clear that some improve
ment is necessary in the Assessor’s hypothesis.
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