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I see I missed the portion of Preston's paper that discusses systematic
error and the ephemerides used by Preston, which were from the Nautical
Almanac of those times.  It follows the table, mostly.  He addresses
some of my questions in that discussion.


On Saturday, Jun 7, 2003, at 10:46 US/Eastern, Fred Hebard wrote:

> In the thread on Maskelyne's tables, George Huxtable very kindly
> provided a link to the late Richard.S.Preston's paper,"the accuracy of
> the Astronomical Observations of Lewis and Clark", downloadable from
> www.aps-pub.com/proceedings/jun00/Preston.pdf.
>
> I read this with great interest, but have some questions.
>
> In the table at the end of the paper, I note that the Lewis & Clark
> latitudes all seem to be out by about 5' of arc.  Is this a large
> amount of error?  It would seem those measurements could be more
> accurate.  I presume Preston used modern ephemerides to calculate the
> positions, but wonder whether the old ones were accurate enough to get
> closer than 5', which then would influence the care with which the
> observations were made.
>
> Bruce Stark has mentioned that he also has become involved in working
> up some of the Lewis and Clark lunar data. From the description in
> Preston's paper, it sounds as if Lewis and Clark took lunars almost
> daily, but Preston summarizes only 20 or so observations.  I wonder
> whether access to the raw data is possible.
>
> Does Preston accurately describe the old methods of using an assumed
> longitude to start iterating toward a more accurate one when
> simultaneous altitudes are lacking?  It would certainly appear so from
> his description.  Our esteemed George Huxtable apparently came to a
> fuller understanding of these calculations more recently, so I wonder
> how Preston stacks up.
>
> I must add a word of thanks to Ken Muldrew for stirring up an
> interesting discussion and prompting George Huxtable to repost the link
> to Preston's excellent (as far as I can tell) paper.
>
> Fred Hebard
>
>
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Frederick V. Hebard, PhD                      Email: mailto:Fred@acf.org
Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
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