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    Re: Nautical astronomy was different
    From: Bruce Stark
    Date: 2004 Oct 21, 14:26 EDT
    Frank,

    You wrote: "
    Your specific interpretation (that lunars did not yield 'time') is clearly your own culinary product. Unfortunately, I think you may have used too much salt."

    Well, I've failed to make my point.

    Later in the same posting you wrote: "
    Maybe you could explain what you mean by 'forcing present-day logic on it'. In other words, what do you think other people have said about lunars that is an example of present-day logic being applied in error?" (For those who haven't been following the thread, "it" is the old nautical astronomy.)

    Glad to.  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?!

    Next, an example of a blunder that was made by someone who supposed, because he understood celestial navigation, that he also understood nautical astronomy.

    Sir Francis Chichester, as we old-timers remember, was famous for his high-speed, single-handed sail around the world. As I recall, he was trying to beat the record of the square-rigged ships that had raced each other around the world trying to be the first to bring the Australian wheat harvest to Europe. But that experience was the very least of his credentials as an authority on celestial navigation. Among other things, he'd written a four-volume treatise on the subject. If you can find a copy of his "Along the Clipper Way," read pages 170 and 171. It's near the end of the chapter on Cape Horn.

    In those pages Chichester mentions his familiarity with Raper's "Practice of Navigation." And, in the same pages, he demonstrates his inability to come to terms with the contents of it. I'll limit myself to one of the ways he demonstrated that.  

    Wanting to look into lunar distances, Chichester turned to his copy of Raper, and was "horrified" by the amount of calculation. Later, pondering the problem of getting GMT from the moon, he came up with a "simple" solution: a way of getting GMT by using the moon's altitude. He had discovered (like others before and after him) the LOP lunar.

    He sent the idea to one of the foremost authorities on the theory of navigation, who pronounced it "elegant," and said that, as far as he could discover, it was new. Chichester, of course was pleased. His only regret was that the idea had not been though of long ago, when it would have been a "godsend to navigators."

    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?

    It seems possible that at least part of the reason was that it wasn't headed "Finding the Time by the Moon's Altitude." The chapter was headed "Finding the Longitude by the Moon's Altitude."

    That would be about a time sight of the moon, wouldn't it?

    Bruce

       
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