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    Re: Maskelyne and his "able computers"
    From: George Huxtable
    Date: 2004 Sep 21, 23:50 +0100

    Frank Reed writes-
    >Shall I add Maskelyne's paper from the Philosophical Transactions of 1764
    >describing how to clear a lunar to my web site?
    Lunar distances were computed in four steps, as I understand it.
    First the position of the Moon was calculated, in terms of ecliptic
    latitude and ecliptic longitude, at noon and midnight, using Mayer's
    predictions. These were VERY complex calculations, so the largest possible
    time-interval was chosen, of 12 hours.
    Then interpolations were made between those positions, to get the Moon's
    position at 3-hour intervals. Because the moon's lat and long vary so
    wildly, linear interpolation wasn't sufficient. Instead, a second-order
    interpolation was done, which took the curvature into account, by looking
    at four successive positions of the Moon.
    Then these 3-hour Moon positions were converted to declination and right
    Then appropriate bodies (Sun or stars) were chosen, East and West of the
    Moon, near the Moon's path and with an appropriate angular distance from
    the Moon for easy measurement with a sextant. Then the angle between the
    Moon and the star was calculated from the decs and RAs.
    The same task was given to two "computers", working away from Greenwich,
    who were not allowed to know of each other's existence. Only if their
    predictions agreed were they accepted.
    On one occasion the computers managed to identify each other and compared
    notes in secret, which led to their instant dismissal.
    Derek Howse, "Greenwich Time and the Longitude", is good on this.
    One of Maskelyne's computers, William Wales, accompanied Cook, as
    astronomer, on his second voyage.
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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