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    Re: Lewis and Clark Celestial Navigation Procedures
    From: George Huxtable
    Date: 2002 Nov 24, 18:31 +0000

    Arthur Pearson asked about the lunar navigation of Lewis and Clark.
    A reference appeared recently on this list to a paper about Lewis and
    Clark's navigation,  The paper was "The accuracy of the Astronomical
    Observations of Lewis and Clark", by Richard S Preston, in Proceedings of
    the American Philosophical society, vol 144, No 2, June 20000, pages 168. I
    think it was available from a website but am sorry to say I have lost that
    address. Arthur would find it a most interesting read.
    That paper referred to an Astronomy notebook kept by Lewis, which contained
    instructions, in manuscript, written by the astronomer Robert M Patterson,
    in the form of solutions to 5 "problems".
    I am most grateful to Bruce Stark (well known to this list), for sending me
    a photocopy from a photographic negative of that Patterson document. It had
    many flaws which made it difficult to read, but I have completed a
    transcription to make it more readily understandable to the reader. I have
    added a detailed commentary to explain aspects of the document to a modern
    reader who is familiar with celestial navigation but unfamiliar with the
    concepts and practices of the early 1800s.
    This has been written in two parts as two separate emails: the first
    dealing with solutions to problems 1 to 3 and the second with problems 4
    and 5, and both these documents need to be taken together. These are long
    emails (and Lewis and Clark may be a minority interest) so I will not
    burden the Nav-L list with them (but if anyone asks for them to be posted,
    I will). Instead, if anyone interested contacts me off-list, I will be
    happy to send a copy directly. If any readers would like to check this
    stuff out and inform me of errors or flaws, that would be appreciated.
    Arhur says- I am particularly curious
    >about how closely their methods conformed to our recent discussion, "Re:
    >Use of Sun Sights for Local time, and Lunars for Longitude".
    I can say that Patterson's writeup has helped me to understand how the
    altitudes of the bodies involved in a lunar can be calculated rather than
    It seems that Lewis and Clark always omitted to measure altitudes for their
    lunars, and instead left them to be calculated at a later date. In that way
    they could avoid setting up a reflecting pool, which would otherwise have
    been necessary for their lunars.
    It appears from the Preston paper that some of their latitude observations
    were greatly in error, which might imply that their use of a reflecting
    pool was somewhat error-prone. However, I have made no further
    investigations of my own into the Lewis and Clark results, nor have I seen
    the Ambrose book.
    George Huxtable
    Arthur Pearson said-
    >Ladies and Gentlemen:
    >I am interested in learning more about Lewis and Clark's navigational
    >procedures.  There has been some tangential mention on this list about
    >their lunar methods of obtaining longitude. I am particularly curious
    >about how closely their methods conformed to our recent discussion, "Re:
    >Use of Sun Sights for Local time, and Lunars for Longitude". Stephen
    >Ambrose's book "Undaunted Courage" provides glimpses into how they
    >worked, including the following:
    >*       In Philadelphia, 1803, Lewis acquired "A Practical Introduction
    >to Spherics and Nautical Astronomy" and "The Nautical Almanac and
    >Astronomical Ephemeris" as well as "tables for finding latitude and
    >longitude" (p. 91).
    >*       At one location along the Missouri, Lewis "measured the distance
    >between the sun and the moon's nearest limb forty-eight times.. He
    >faithfully recorded whatever he could whenever he could, leaving up to
    >experts back east to work out the meaning of the figures" (p. 148).
    >*       Ambrose states that "...he wrote a thousand-word description of
    >the instruments he was using, how he was using them, what he was
    >measuring, and so forth.  It seems Lewis wanted to be as sure as he
    >could tat someone someday would take all his figures and make some sense
    >of them."
    >Has anyone on the list examined that thousand word description of how
    >Lewis made his celestial observations?  Would the tables he acquired in
    >Philadelphia have been Bowditch's recently published "New American
    >Practical Navigator"? Is there an essay or paper anywhere on this topic
    >of his celestial procedures? Any insight or direction to additional
    >sources would be most welcome.
    George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    Tel. 01865 820222 or (int.) +44 1865 820222.

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