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    Re: Maury and Spooner on longitude at sunset
    From: Frank Reed
    Date: 2015 Oct 21, 09:12 -0700

    Rommel wrote:
    "He [Joshua Slocum] used what was a nice mantle clock of his day for a chronometer and if he had anything like a sextant no one really knows."

    That's wrong. The little clock which Slocum took with him aboard Spray was not a "nice mantle clock," and he did not use it as a chronometer. It was a tiny, "tin" alarm clock, about three inches wide, two inches tall, and one inch deep. Its clock face was the size of the face on an old wristwatch! It was just fine for keeping track of dead reckoning and planning the events of a single day, but it did not serve as a chronometer, except in the very crude sense by which he could detect the approximate change in longitude from sunrise to sunrise and noon to noon (if you're changing your longitude by three or four minutes of time daily, and your clock is accurate to 30 seconds a day, you'll notice the daily changes even though the clock would be hopeless as a chronometer). As for a sextant, of course, he had one, and yes, we do know this. He proudly displayed his beat-up old sextant to anyone who was interested after he returned from his circumnavigation.

    While I'm here... in case anyone is thinking of it, no, Joshua Slocum did not sail the globe "using lunars". Although Slocum shot one lunar approaching the Marquesas and wrote about it beautifully in his book, that was the only one that he shot for at least two-thirds of the circumnavigation. When Slocum informs us that he sailed by the "old ways" he apparently means dead reckoning for longitude and noon Sun for latitude, which was the standard navigational methodology aboard many American vessels even in the 1830s. It's certainly possible to sail around the world using only dead reckoning for longitude. Scientific navigation was invented to make voyages faster, more efficient, less risky. It didn't make sailing over global distances possible... it made it "profitable" --in the broadest sense of the word. Joshua Slocum was a "yachtsman" ...a yachstman on a frugal, pennies-a-day budget, to be sure, but he could pick his sailing times and his courses as they suited him. There was no rush, no cargo to deliver, no battle to be won. That's how Slocum was able to leave behind most of the tools of celestial navigation (except noon Sun for latitude). He didn't need a chronometer or time-keeping... because he was a man of leisure.

    Frank Reed
    Conanicut Island USA

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