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    Re: Lunars
    From: Fred Hebard
    Date: 2007 Sep 24, 07:11 -0400

    I fail to understand what the date of invention of the quadrant has
    to do with the accuracy set for the longitude prize.  It would seem
    that John Karl's explanation may be correct, in that the advisors to
    Parliament may have recommended setting the accuracy to 30' because
    they figured that lunars would be the method chosen and that 1' of
    arc was about the limit of accuracy for such a measurement,
    regardless of the instrument.
    Fred Hebard
    On Sep 24, 2007, at 12:18 AM, frankreed@HistoricalAtlas.net wrote:
    > And you asked:
    > "BTW, in the book I make the observation that the sun-moon distance
    > changes
    > about one minute of arc per two minutes of time.  So to do better than
    > finding UT to with one minute requires some pretty adroit
    > observing.  And if
    > the LD distance were accurate to one minute of arc, the longitude
    > would be
    > accurate to only about 30'.  Doesn't this explain why the  famous
    > British
    > Parliament Prize was for determining longitude better than 30' of
    > arc?? "
    > Nope. Just a coincidence. The prize rules were set in 1714. That's
    > even
    > before the invention of the reflecting octant, which soon led to the
    > sextant. In 1714, it was still harder to imagine measuring the lunar
    > distance at a sufficiently accurate level for determining a useful
    > longitude. Typical latitude measurements using the non-reflecting
    > instruments of that era were known to be accurate to roughly +/-10
    > minutes
    > of arc --sometimes better, sometimes worse.
    >  -FER
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