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574 SWEDENBORG AS A MAN OF SCIENCE. [Doc. 200 .
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When the compass was handled and replaced
under the thread, the needle indicated 8 ° 45’.
After being disturbed by a key go 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 that locality of . 8° 49’.
The difference between my computed declination which is
8 ° 52’ and that which resulted from observation is merely three
minutes ; but if a mean is taken between the first observation
8° 53’ and the second or last 8 ° 52’, the difference is merely
half a minute, which amounts to nothing.
The reason why my computation is so prolix and difficult,
consisting of 28 operations for finding out each declination,
is, that I have to transfer the fluxion of a perpetually spiral
vortex — which is really the origin of the declination of the
magnet - from an algebraic to a trigonometric and arithmetical
computation; and, indeed, without any assistance derived from
previous experiment or trial.
I have to observe that I assumed the eastern longitude of
Upsal from London to be fifteen degrees, in consequence of
information I received in 1710 from the celebrated astronomer
Flamsteed,56 at Greenwich, when I brought him the obsery
ations of two lunar eclipses made by the late Professor
Elfvius,54 which he at once in my presence compared with his
own observations. As soon as I shall be kindly informed of
the approximate longitude and latitude of Torneå, I am ready
to make, and to communicate, a computation for the year 1736 ;
where I am certain a similar result will be obtained to that
which follows herewith.
If any one now, under proper instruction, took the trouble
to compute the declination of the magnet for every fifth degree
of latitude and longitude over the whole globe, between 65
degrees north and south, and also every td or fourth year;
and if afterwards he published his computed declinations either
in the form of an ephemeris or of a chart, it might be deter
mined thereby as well by land as by sea under what degree
in an eastern or western direction any one is or sails; pro
vided the declination of the magnet and also the latitude are
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