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    Re: Bligh's noon by chronometer
    From: Frank Reed
    Date: 2010 May 31, 06:25 -0700

    George, you wrote:
    "And then, the latitude could be readily calculated
    from the altitude at that moment, knowing the time difference from noon,
    using the Ex-meridian Tables. That was primarily what those tables were
    for."

    Sure. Of course. The fact that Bligh mentioned these "exactly at noon" sights suggests he didn't know ex-meridian sights or didn't find them convenient. The "ex-meridian" method in general was certainly available at an early date but it may not have gained much attention as early as 1788, and it didn't have that catchy name yet. In the 1790s, it's in Moore under the heading:
    "To find the Latitude by one Altitude of the Sun, when the Time is not more distant than one Hour from Noon".
    And of course, it's in Bowditch, tied up a bit, a few years later under the title:
    "To find the Latitude by one Altitude of the Sun, taken near noon, having the time of observation by a well regulated watch".

    Did Bligh really get any advantage beyond calculational convenience from a sight "exactly" at noon as opposed to ten minutes from noon (where the time of noon has been determined from a morning time sight advanced by the dead reckoning)? Or did he not have the nececssary "algorithms"? In other words, if he had taken the Sun's altitude ten minutes from noon, would it have made any material difference to the accuracy of the resulting latitude if he knew the calculation? Or did he simply not know how to do it? I am just posing this as a general topic of discussion. Go wherever you want with it (anyone).

    Speaking of the Devil, I wanted a photo of a Bounty replica for the talk I'm doing after dinner Saturday night so I went here http://www.tallshipbounty.org/. I found a good photo, and just for fun I checked the vessel's current position on that web site. It turned out it was about ten miles from Mystic, Connecticut. Small world! For a moment I thought about borrowing the ship itself as a prop for the talk. Alas, it was a position that was nearly two weeks old so the ship has moved on and will be a couple of hundred miles away instead. But it's coming to Chicago in August; I'll go grab my own photo then.

    -FER


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