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    Lewis and Clark journey: the Astronomical Notebook.
    From: George Huxtable
    Date: 2003 Mar 4, 07:49 +0000

    Lewis and Clark journey: the Astronomical Notebook.
    I have made a transcription of a manuscript document, written by the
    astronomer Robert M Patterson, that Lewis and Clark took with them on their
    famous overland journey  to the Pacific in 1804-6. This became part of the
    Astronomical Notebook of Meriwether Lewis. The document provided advice on
    to the travellers on the astronomical navigation in terms of the solutions
    to 5 "problems".
    Attempts to make this transcript available to a wider readership in the
    form of multiple emails have been unsuccessful, partly because the
    line-wrappings that email transmission inserts disrupt the layout of the
    tables. It became clear that email was not a suitable medium for such a
    I have now put this  information onto a website at-
    which is named-
    "Lewis and Clark journey: the Astronomical Notebook". It comprises the
    transcribed manuscript plus a full commentary to explain any aspects that
    would be unfamiliar to a modern sextant navigator.
    If any reader has difficulties in displaying this, with its monospaced
    table layout, in his browser, I would like to know. Also, I would be happy
    to receive questions and criticisms about its contents.
    It should be read in conjunction with the paper by the late Richard S
    Preston, "The accuracy of the Astronomical Observations of Lewis and
    Clark", in the proceedings of the American Philosophical Society, Vol 144,
    No 2, June 2000, pages 168 to 191, and downloadable from-
    Although Patterson's contribution appears to be very competent, I doubt if
    the travellers considered it to be "user-friendly".
    An interesting aspect of their observations is this-
    I understand that the travellers took with them a sextant and an octant,
    and it was always the octant that was used for their altitude observations.
    Why, I wonder?
    Because there was (of course) no sea horizon to be seen, the travellers had
    to use an artificial horizon, the reflection from a liquid surface in a
    bowl. Because of this reflection, the measured angle is double the
    In Summer, noon Sun altitudes will exceed 45 degrees, so then, the
    measurement will be outside the normal 90 degree span of an octant. The
    octant was fitted for use by back-observation, in which case the range can
    continue beyond 90 degrees. However, when using back observations, I know
    of no way of establishing the index error of the octant. Any suggestions
    from readers?
    Did the travellers then have to assume that over the whole course of the
    journey, despite all the bumps and temperature and humidity changes, a
    wooden octant retained its index error unchanged, perhaps at zero? To me,
    such stability seems most unlikely. If L&C assumed that was the case, to me
    it throws considerable doubt on the accuracy of all their observations of
    altitudes above 45 degrees. Using a sextant would have allowed the
    index-error to be zeroed and accurate altitudes obtained, up to 60 degrees.
    Were the pair competent celestial navigators, I wonder? Reading Preston's
    paper, in his table on pages 185-6 there seem to be major discrepancies
    between their measured latitudes and modern latitudes of positions that are
    supposed to correspond. I think there's some interesting study-work yet to
    be done on these records.
    However, I do not profess to be at all knowledgeable about the Lewis &
    Clark journey myself.
    George Huxtable
    contact George Huxtable by email at george@huxtable.u-net.com
    or by phone at 01865 820222 (from outside UK, +44 1865 820222)
    or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon, UK.

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