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DOCUMENT 42.
PROF. ELFVIUS54 TO SWEDENBORG . *
Upsal, July 28, St. Swithin’s day, 1711.
Most honoured Mr. Swedberg,
My good old friend and cousin,
With great joy I read your letter to the
Librarian ; from which I not only learn that your health is
good, but also that you apply yourself with most praiseworthy
industry to the study of mathematics, and the things belonging
thereto. Of this I am heartily glad, and I wish you all success
in accomplishing your laudable design. I am coming to you
now with a few small matters, which I should like to know
myself, and which may also be of some use to you in your
pursuits.
1. That you try to be present, at all hazards, while Flam
steed is making some observations; that you notice how
he conducts them ; that you describe bis instruments with all
the apparatus belonging to them, and especially the diopters,
whether they are provided with a movable limb, after the
manner of Hedräus, or with cross-lines, as is the case in
Tycho’s instruments, or with a screw in the limb, which
Robert Hooke so strongly recommends, against the opinion
of Hevelius; also whether he uses a telescope in the place of
the diopters, and how it is fastened. How the instrument is
placed parallel with the horizon ; and especially that you find
out all about the micrometer, which is placed inside the tube,
* Benzelius’ Collection, Vol. XL, No. 67.
+ Lars Spole (when ennobled Rosenborg), brother of Mrs. Elfvius,
married Magdalena Schönström , cousin of Emanuel Swedenborg, on the
ground of which relationship Prof. Elfvius addressed Swedenborg as cousin .
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