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    Re: Point Venus, May 1774
    From: Alexandre Eremenko
    Date: 2007 Apr 29, 14:46 -0400

    
    Dear George,
    
    > | My calculation outlined in the previous message implies
    > | that the going of the Clock from May 2 to May 6 was
    > | approx 22m33sec per day.
    >
    > I think Alex has corrected those numbers in a later message.
    
    Strictly speaking this statement was correct.
    But part of this "going" 1m 22s was known to the astronomers
    of the Cook expedition, ant it was pretty constant.
    Another part is due to the fact that this was a
    "syderal clock". Showing syderial time rather than
    the mean solar time.
    
    > | What sort of "astronomical clock" was this, I don't know.
    > | And why did not they use chronometers instead.
    
    This stement I indeed corrected in my second message.
    The Clock was OK, in the sense that its "going"
    against the syderal time, was constant, and known to
    the astronomers of the Cook expedition.
    
    > Cook didn't have a chronometer,
    > on this, his first voyage. Anyway, on land,
    
    George, this is a misunderstanding.
    I was talking all the time of Cook's SECOND voyage.
    (The dates of observations I am speaking about
    are early May 1774.
    He DID have a chronometer in this voyage.
    
    > should be better than any early chronometer.
    
    It should. When used for observations on land.
    It did not show any absolute time,
    but only relative time (since it was landed and started)
    I did not
    investigate whether its going during a week ot two was
    better or worse than that of their chronometer.
    
    > When you are comparing Cook's altitude
    > observations, what times are you
    > using? Remember, he used apparent time,
    > as did the Almanac then, whereas
    > modern calculations expect GMT.
    > Has that been taken into account?
    
    Sure. As I said I don't use Cook's clock at all.
    I use the true GMT.
    This true GMT is derived from Cook's Sun altitude.
    Assuming that his Sun altitude was very close to
    the true value, because they used the
    "astronomical quadrant" for this.
    
    Strictly speaking, what I am saying is that his
    sun altitude (taken with astronomical, art horizon quadrant)
    is INCONSISTENT with his Moon altitude (taken with I don't
    know what, some sextant or quadrant with respect
    to the real horizon, I suppose).
    Inconsistent in the sense that there was NO TIME
    when these two altitudes were as Cook recorded.
    
    Alex.
    
    
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