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Everyone knows Dresden art galery with its famous Sixtine Madonna
by Rafael:-)
But there is a less known place nearby:
the Museum of Mathematical Instruments.
They have many wonderful things including  a globe
made by Merkator himself, and Hershel-made telescopes.
(And Pascale's own computer, and many star and Earth globes ranging from
XVI to XX century, chronometers etc.)

On the Cel Nav side, they have an octant in excellent condition
(J. Makrow 4 Upper East Smithfield, London 1845,
ebony/brass) and most interestingly,

A Troughton reflecting circle No. 131.
I made careful sketches of it.
Hope to be able to answer any questions about it.
The circle is 1.5ft diameter (445 mm),
it has silver scale divided to 10' and nonius to 10".

There are actually 3 arms with 3 noniuses (verniers).
The rays are crossing (see our previous discussion on
reflecting circles initiated by George), and there
is indeed a "dead range".

The device is in excellent condition, made in 1780,
and even the  mirrors look great:-)

I spent a lot of time looking at it, and only after that
went to see the Sixtine Madonna:-)

Alex.

P.S. Also made a careful examination of the octant.
It looks like a cheap variety: there is even no index
mirror adjustment. (However the horizon mirror has two
skrews as on the modern sextants).

A

   

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