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    Re: Jack Aubrey's fixing of longitude
    From: Frank Reed
    Date: 2011 Jun 20, 14:55 -0700

    Geoffrey, you wrote:
    "I think the observation may have been supposed to be a lunar
    occultation of Venus. But I cannot make sense of "Two seven four" as a reading."

    The only thing I can think of is some number of seconds of time. They would have needed an accurate time sight for local apparent time just before the occultation in order to convert it to a longitude. We could imagine they made that local time observation, maybe using a leveled instrument like a theodolite to get the exact altitude of the Sun or perhaps Venus. At the instant that observation was made, an assistant would start counting seconds (with a swinging pendulum?). Two observers with two telescopes observe Venus slide behind the limb of the Moon. This can take more than a minute. Ever seen the Moon occult a planet? It can be quite dramatic. When the last bit of Venus disappears, each observer would note the seconds and call out that number: "two seven four". While this "fits" reasonably well as far as I can see, it's just a guess, of course, since there is no further detail in the novel.

    Incidentally, this would count as a very exotic observation. It's the sort of thing that might have been done by a professional astronomer on a voyage of exploration but would be really unlikely on an ordinary Royal Navy vessel. It adds to the "larger than life" character of O'Brian's heroes.


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