Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Accuracy of Lewis and Clark Observations
    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
    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
    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
    Speaking of time, I've run out of it. Will try to get back to this tonight.

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site