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Subject: Lewis and Clark journey: the Astronomical Notebook.
From: George Huxtable (george@XXX.XXX)
Date: Tue Mar 04 2003 - 02:49:43 EST
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
document.
I have now put this information onto a website at-
www.huxtable.u-net.com/lewis01.htm
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-
www.aps-pub.com/proceedings/jun00/Preston.pdf
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
altitude.
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
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contact George Huxtable by email at george@XXX.XXX
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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