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Gary LaPook wrote:

I don't know what happened there in May, 1774 but I do know what
happened there on July 11, 2005, I sat there with my sailing crew
drinking Hinano beer! The area is a park now with a lighthouse and a
commemorative plaque to the 1769 expedition.



On Apr 24, 8:24 am, alex  wrote:
> What exactly happened in Point Venus in Thaiti
> in the first week of May, 1774?
>
> Point Venus, S 17d29'8, W 149d29.6 (from Terraserver)
> In the records we find the following data:
>
> date, time-by-the-clock,
> zenith distance of the Sun,
> altitude of the Moon,
> distance from the Sun to the Moon,
> Barometer, thermometer,
> derived longitude. Errors of the Quadrants (all three).
> No dip or alt above sea level is recorded.
>
> The question is what can we do with these data.
> Let me try to assess the reliability of each piece.
>
> Time-by-the-clock seems pretty useless;
> my preliminary investigation shows that this was a really
> lousy clock (see below).
> Zenith distance of the Sun seems to be the most reliable
> number. It was taken by an "astronomical quadrant"
> A stationary one, of the type of transit/theodolite,
> I suppose. And it took the zenith distance rather
> than altitude, so I suppose it is dip-independent.
> The Error of this quadrant is recorded as 21",
> a quantity one can neglect for the first approximation.
> (See below why I prefer to neglect their recorded IC,
> at least in the first step of this investigation).
> The altitudes and the distances were recorded
> "as read on the sextant scales", no corrections added,
>
> The main problem is to determine the GMT of each observation
> as precisely as we can.
>
> I used the following method. For the given date,
> I determine GMT from their presumably
> most precise observation, the Sun zenith distance.
> I use Frank's calculator to do this.
>
> The procedure is exactly the following.
> I take their Sun ZD, convert it to altitude,
> subtract refraction and add/subtract Sun SD,
> according to the limb observed.
> Then I find by trial-and-error, using the Frank
> calculator, the GMT of the moment when the Sun was
> on this altitude on that day, in their position
> (Terraserver position).
>
> Then I use this GMT, and this position, to compute
> the rest of the quantities: Moon alt, and Sun-Moon dist.
> Then I reduce their Moon alt using parallax, refraction
> and Moon SD.
> Then I record the errors:
> a) of their watch, as compared with GMT
> b) of their Moon altitude and
> c) of their Lunar distance.
>
> 1. The clock was terrible. Going 1-2 MINUTES PER DAY!!!
> Irregularly. They should had better used a sandglass:-)
> I conclude from the citation below that the clock was
> regulated to sideral time, rather than mean solar time,
> but in any case, their time records do not help in
> determining the GMT with reasonable precision.
>
> It is very interesting, what Wales (the astronomer
> in this expedition) says about this clock:
>
> "...it may not amiss to take notice of some
> very extraordinary irregularities, which happened to
> the going of the Clocks..."
>
> "The Clock B lost 1m22s a day on syderal time at Otaheite,
> lat 17d29'1/4 S and long 210d25' E from April 23d
> to May 9th, 1774; but I here reject its loss
> between April 30-th and May 1st,
> as it appears to have lost exactly 1m more on that day
> than on any other;
> a circumstance I cannot account for PROPERLY,
> as I never, that I know of, left the case or face of
> the Clock unlocked." And  he continues:
>
> "There is however little doubt but that some WITTY
> Gentleman or other found means to open it, and put the
> Clock a minute back,
> I suppose to try whether or no the
> ASTRONOMER could find it out."
>
> (Astronomical Observations... p. xvi. Emphasized words
> are in his text). I suppose when he says 1m22s a day
> he means that the AVERAGE LOSS was 1m22s EVERY DAY.
> I only investigated 3 days so far (May 1-3).
>
> And I have to say that they were negligent in recording
> the date, but this is easy to fix.
> (For example, they never make clear whether they record
> the local date or Greenwich date, and how do they count the
> local date. Given that their longitude was
> "210 East" as they say:-) this makes the thing puzzling
> in the beginning. But I was able to fix all GMT dates
> beyond reasonable doubt:-)
>
> This message is too long. I will continue in the next one.
>
> Alex.


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