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    Re: Nautical astronomy was different
    From: Frank Reed CT
    Date: 2004 Oct 24, 02:39 EDT
    Bruce S wrote:
    "First, an example of the sort of thing that can baffle a navigator who's unfamiliar with the old way of thinking. This is from an 1859 edition off Bowditch, in the chapter on lunar observations. Under "General Remarks . . ." Bowditch has this to say:
       'The accuracy of a lunar observation depends chiefly on the regulation of the chronometer, and on the exact measurement of the angular distance between the moon from the sun or star; a small error in the observed altitudes of those objects, will not in general much affect the results of the calculation.'
    The accuracy of a lunar depends on the regulation of the chronometer?! "

    It's an imperfect book. I believe that what we're seeing here was probably nothing more than bad editing on the part of N.I. Bowditch (son of the original N. Bowditch who had taken over a fair share of the editing before N's death and, naturally, all of it after 1837). If you look at editions of Bowditch from 1826 (the latest I can conveniently check) and earlier, the language is almost identical to what you've quoted above except that it says, "the accuracy of a lunar observation depends chiefly on the regulation of the WATCH.." (!!!). This was changed in later editions. I suspect that someone went through the text and replaced watch with the more fashionable word 'chronometer' without thinking about the significance. I think it's important to remember that Bowditch (the original) was in the insurance business for most of his adult life. He was not a seafaring navigator after the publication of the earliest edition of the New American Practical Navigator, and his mathematical hobby had shifted to the Mecanique Celeste. He did not experience the rapid rise in popularity of chronometers, and they did not interest him. Like many of us on this list, he was passionate about lunars because they were an interesting intellectual challenge. In later editions of the Navigator, N. Bowditch treated chronometers as an after-thought. He did understand from the earliest days that a navigator shooting lunars could benefit greatly from an ordinary pocketwatch. The watch would be set to Local Time from a time sight when convenient. "Regulating" it means "setting" it. Then the lunar's Greenwich Time would be compared against the local time. An ordinary watch might be unreliable over longer time periods, but he saw it as an excellent means of carrying the results of a time sight forward into the day.

    Bruce S also wrote:
    "To come to my point, Raper devotes a chapter to getting Greenwich time from the moon's altitude. The method explained there makes the LOP approach look like a Rube Goldberg contraption. It is brief, and the working of it is free of those loose joints. How could Chichester have missed that chapter? For that matter, how could the other authorities who endorsed the LOP lunar, or invented it themselves, have missed it? "

    Because no great weight is attached to a dead science? There was a lot of crap written about lunars after they became largely irrelevant to practical navigation in the latter half of the 19th century. There probably will continue to be in years to come. Then again, I anticipate some great things being written about lunars in the near-term...

    What you've written about Chichester and all is certainly a good and important lesson, but I really don't think it's relevant to your initial points about how 19th century navigators had some radically different perspective on time and longitude. I do not believe that they did.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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