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    Preston's paper on Lewis & Clark's Navigation
    From: Fred Hebard
    Date: 2003 Jun 7, 10:46 -0400

    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
    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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