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Subject: Preston's paper on Lewis & Clark's Navigation
From: Fred Hebard (Fred@XXX.XXX)
Date: Sat Jun 07 2003 - 10:46:02 EDT
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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