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Re: Accuracy of Lewis and Clark Observations
From: Bruce Stark
Date: 2002 Aug 8, 15:40 EDT
From: Bruce Stark
Date: 2002 Aug 8, 15:40 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