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    Re: Old Style Lunar
    From: Ken Muldrew
    Date: 2005 Jan 11, 13:16 -0700

    On 11 Jan 2005 at 15:02, Frank Reed wrote:
    > "The airport elevation at Rocky Mountain House, Alberta is 3,242  feet."
    > Which would decrease refraction values (absolute values) for all altitudes
    > below 45 degrees by more than a tenth of a minute of arc --and increasing
    > to 0.5  minutes of arc at 10 degrees altitude (10% of the standard sea
    > level values).  Did Thompson correct for this?
    I don't think so, but his journals are just too devoid of details to know
    for sure. He always records temperature so I might be able to discover
    whether he takes that into account by re-doing one of his calculations
    where the temperature is quite extreme.
    > Most accounts of lunars were
    > written for observers at sea level, literally. Of course, if he measured
    > barometric pressure  at all, I suppose it would necessarily have been with
    > a barometer calibrated at  low altitude which would account for refraction
    > at mountain altitudes automatically (assuming he had tables that covered
    > such low pressures).
    There are some instances where he determines barometric pressure by
    measuring the boiling point of water, but only in high mountain passes. I
    doubt that he accounted for pressure elsewhere on his travels. I was just
    wondering if the apparent systematic error in his latitude data might be
    from neglecting the altitude.
    Ken Muldrew.

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