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George,
I suspect that there are some
substantial (mathematical) problems
with back sights in general,
not just the rigidity of an instrument.

All papers on the subject I read yesterday
are divided into two categories:

a) papers of theorists (like Wollaston,
who did not actually sail, and I probably did
not experiment with a quadrant)
and

b) papers of people who actually tried the back
sights.

Wollaston proposed exactly what I proposed:
measuring the dip, and the procedure of
back sight index correction.

However all who actually tried repeat that
this does not work.

As a result, they soon gave up the idea of
taking back sights. I am trying to understand mathematical
reasons of this. I just don't believe that the
main obstacle could be in sextant/octant rigidity:
they knew very well how to make good instruments.

Alex.

   

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