Early Telescope

[ReneZ]

There's an article about it, retrievable on-line, in German:
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In the right margin there's a button for the PDF copy of the whole article.
Even if you can't read it, it's worth looking at its several illustrations

This discusses three versions of this illustration:
One in MS St.Gallen 18, p.45, from approx. the year 1000,
one in MS. Vat.Lat. 644 (10th Century), and one in Venetian MS Marc.Lat.VIII from the
12th-13th Century. That is the one you were showing here.
Another illustration is from a MS lost in 1944.
As the article describes, the tubes were used to look at stars. First they were oriented to the celestial
pole. After that, they would compare the positions of stars circling around the pole with a chart with
24 radii, and be able to tell the time during the night.