NavList:

   

Reply

Ken Muldrew said-

>George mentioned that we shouldn't take the ease with which we read
>off a second hand for granted when considering the difficulties
>encountered by these explorers. Although it seems likely that Lewis,
>as presidential secretary, would have owned a pocket watch and been
>reasonable adept at reading it, he may have recruited an assistant to
>observe the watch when making observations to improve accuracy. I
>presume this is what George is suggesting may be the reason for the
>frequent one minute errors. This explanation does seem to be quite
>compelling. I wonder if the errors persist when the expedition was in
>the neighborhood of the big bend of the Missouri, at the Mandan
>Villages, since they had an accurate map of that region.

Response from George-

Yes, that's just what I was suggesting.

Well, I'm working a long way downstream of the Mandan villages, still
moving up the Mississippi, with L&C, toward St Louis. And at present I have
no ambitions to proceed beyond the borders of Missouri state, all contained
within Moulton Journals, vol 2.

But in answer to Ken's question, I've seen a record of L&C's observations
at winter camp at Fort Mandan, an equal-altitude measurement dated Feb 23
1805, in which it appears that those timing errors of 1 minute were still
being made. This is in Moulton vol 3.

L&C had attempted to determine the longitude of that camp by timing an
eclipse of the Moon, which in itself is not very accurate because the
Earth's shadow is rather fuzzy. However, they made matters worse by
confusion about whether the event was predicted in mean or apparent time,
and failed to allow properly for the large variations that were occurring
in the chronometer rate, so those 1-minute timing errors were not very
significant in that context.

As a result of all this error and confusion, L&Cs longitudes were nearly 90
miles out, whereas previous measurements at the Mandan villages by David
Thompson were within 10 miles. Thompson was a much more experienced
explorer and surveyor, who knew exactly what he was doing with celestial
navigation.

For anyone interested in Fort Mandan, the reference I gave in an earlier
posting has two papers, one by Bergantino about its longitude, the other by
Rudner and Heynau about its latitude. It's at-
"We Proceeded On", vol 27 no 4 (Nov 2001), the quarterly journal of the
Lewis and Clark Trail Heritage Foundation, inc, at 406/454-1234 or
www.lewisandclark.org  ; they will sell back numbers at a modest price.
That issue is a worthwhile buy for anyone interested in the L&C celestial
nav.

===============

Doug Royer ( in a message from Dick Savage) makes an interesting mention of
an account by Stephen Ambrose about timekeeping in 19th century America. He
is an author new to me and I wonder if Doug can provide a more detailed
reference.

In England, church clocks were very common aound 1800, and some of the
older clocks then had only an hour hand. A few of them, to this day,
possess only an hour hand, which was good enough for anyone in the 18th
century. Presumably the sexton, guided by his sundial, would set his clock
to strike in synchronism with other churches that he could hear striking in
adjacent parishes, in those quieter times. In England, parishes were small
enough, and parish churches close enough, that several others would usually
be in earshot. However, the velocity of sound must have perturbed any such
attempt.

George.

================================================================
contact George Huxtable by email at george@huxtable.u-net.com, by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
================================================================

   

Reply