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    Re: ? ? ? David Thompson's Navi gational Technique
    From: Bruce Stark
    Date: 2004 May 30, 20:37 EDT
    Ken,

    Thank you for the valuable David Thompson information. For a long time I've wanted to know something about him. Having an example of his navigation is worth a lot.

    Like George, I'm surprised he took six measurements of the sun's altitude for a time sight. Clearly, he didn't mind a little extra arithmetic.

    Also surprising is that he seems to have taken his courses from the sun, when it was out, rather than from a compass. That's pretty much standard for outdoorsmen when the sun isn't too near overhead, but Thompson must have been unusually good at it.

    The business of proportioning for the distance that fit his supposed Greenwich time, and comparing his cleared distance to it, strikes me odd. At present I can't think what the advantage would be. But, then, I can't think of any disadvantage either. Probably the difference between the Greenwich time per dead reckoning and the Gr. time per lunar wouldn't be enough for the moon's actual, as opposed to her average, orbital speed to have much effect.

    The beauty of Thompson's way is that it highlights something special about the old navigation. As you  say: "He never bothers with a corrected Greenwich time because he deals only in local time. Greenwich time is merely for taking values out of the Almanac."

    His concern is longitude, not the time at Greenwich.

    Bruce
       
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