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Subject: Re: Accuracy of Lewis and Clark Observations
From: Bruce Stark (Stark4677@XXX.XXX)
Date: Thu Aug 08 2002 - 15:40:26 EDT
George may be new to Lewis & Clark, but he's already focused on the important
questions.
Bill Noyce has given a good answer to the first question, but I have more to
add on that subject. The chronometer was an Arnold, one of the best.
Bergantino figured it stopped or ran down about twenty times as I recall. Not
surprising, considering the conditions of the trip. The instrument's main
value was in keeping track of elapsed time, not Greenwich time. Navigation
manuals through the middle of the nineteenth century show how watches and
chronometers were used. Lewis and Clark seem to have followed the usual
procedures.
It didn't matter what Greenwich time was. Whatever the chronometer read when
a morning or afternoon time sight was taken showed how fast or slow it was on
local time. That's what time sights were for, to find the time. "Time" always
meant local apparent time unless the label or context made clear otherwise.
Lewis and Clark used equal altitudes instead of time sights, but to explain
why they did so would take us off in another direction.
When a lunar observation was taken the chronometer reading was recorded along
with each distance. The difference between local time, per chronometer, and
Greenwich time, per lunar, gave the longitude-by-observation.
Also, as Bill pointed out, if the chronometer could carry the local time of
camp "A" until you were at camp "B" and got an observation for local time
there, you had the difference of longitude between camps. So if you'd
established a good longitude at "A" you also had a good longitude for "B."
All the equal altitudes, lunars, and time-azimuths were timed with the
chronometer. It's just that the chronometer didn't tell what Greenwich time
was.
Speaking of time, I've run out of it. Will try to get back to this tonight.
Bruce
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