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    Re: Easy Lunars in 1790
    From: Ken Muldrew
    Date: 2006 Apr 27, 14:09 -0600

    On 27 Apr 2006 at 15:55, Fred Hebard wrote:
    > On Apr 27, 2006, at 3:38 PM, Ken Muldrew wrote:
    > > Note: I haven't corrected the data for temperature or pressure (his
    > > altitude above sea level was about 3250 ft.).
    > >
    > Ken,
    > Depending upon the temperature, pressure can add a fairly significant
    > correction, especially at 3250 ft.  Here at 2000 ft one almost drops
    > off the bottom of the Nautical Almanac correction chart.  Did
    > Thompson record barometric pressure?  I would think he might have
    > done this for height above sea level determinations.  If so,  I would
    > expect he also would have recorded temperature.
    There are a couple of cases in mountain passes where he records the
    boiling point of water to measure his altitude (and my recollection is
    that he substantially overestimated that altitude) but in general he does
    not record barometric pressure. I haven't found a case where he adjusts
    for temperature, but when he requested thermometers, his reason was for
    correcting for refraction. Most of my recalculations have been for lunars,
    which are too involved to be sure of a temperature allowance. When I find
    the time I'll look at some meridian altitudes to see if he compensated for
    temperature on a regular basis.
    Ken Muldrew.

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