Next message: Bill: "Re: Instumental error?"
Fred,
I apologize to you and to the list:
I mistyped the web address.
The corrected address is:
http://adsabs.harvard.edu/cgi-bin/
nph-bib_query?bibcode=1888AN....118Q.383S&db_key=AST
(Again, remove carriage return!)
In general, this archiv contains about 30 XIX century
papers with keywords "sextant", "errors", "eccentricity" etc.
I am glad it is free.
The author speaks of a meridian circle rather than a theodolite.
Somehow on the first reading I had a wrong impression
that the trick can be done with an ordinary theodolite.
But when I started to explain this to the list, I encountered
difficulties, so I looked at the paper again, and noticed that a hudge
objective lens is required.
The ordinary methods involving theodolite are probably
the "outdoor methods". I mean you put some vertical sticks
on a large distance from your position, and measure the horizontal
angles with your sextant and then with theodolite.
The large distance is required because you cannot assure
that both measurements are exactly from the same position.
For example, if you need 0.1' precision, and are
able to keep the position to 1 inch (I doubt is is easy to
do better than that,
even with sophisticated tripods), the sticks should
be at the distance of 3400 feet which is hard, of course.
Any indoor method I can imagine would use one or several reflecting
surfaces, but the problem of crating parallel rays is hard.
Alex.
