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Ken,

> You wrote:

> Were these altitudes taken at
> night using a sea horizon? (...one last hope
> for a sensible explanation).

No, they were taken in conjunction with Sun-Lunar
distances. Thus Sun was shining.

On May 1774 (my first two postings under Point Venus)
they were taken with ordinary sextant/quadrant,
against a sea horizon, but the height of the observer
over the horizon was not recorded.

On August 27 1773 (my last posting on Point Venus)
they were taken with astronomical quadrant using
a plumb line instead of the horizon.

I have the following possible explanation.
The timing of these altitudes was not done carefully.
Presumably they used one clock with which three
simultaneous observations were timed
(Sun alt, Moon alt and the Lunar).
Of course they took most care to time the Lunar.

So perhaps when the guy taking the lunar said "Now!"
the person in charge of the clock recorded the time.
The two other guys taking altitudes did not give
separate commands to record the time, and tried to
record their altitudes approximately at the time
when they heard this "Now" signal.
This could easily lead to several seconds or more mismatch
in the timing of altitudes. And the altitudes change
quickly...

This is my conjecture.
In any case it seems clear that they did not really care
much about accuracy of these altitudes.
Perhaps they dod not inspect the verniers with magnifying glass
being afraid to miss the next "Now" from the Lunar guy.
But I even don't know whether their
sextants/quadrants were equipped
with any magnifying glasses. Probably not, as they had
large radii.

There can be other explanations as well: the corral reef/waves
obscuring the horizon under Moon... etc.

Alex.




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