NavList:

Dear George,

Thank you very much for your reply.

I wish to cover some aspects of it in further detail as follows :

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Kermit asks several relevant questions, and I will offer some "informed
guesses", and suggestions.

"1 - We are to assume that all observations are supposed to be made on
board a non-moving vessel and at the very same time."

No, they will mostly have been made from a vessel under way, except for
those taken in harbour at the foot of that page. However, each
corresponding set, of lunat distance and altitudes, may well have been
taken simultaneously, as such vessels were well-manned, with a number of
competent observers on board, and provided with two brass sextants, and
most likely a number of wooden octants, good enough for taking altitudes. I
imagine the Navy making a bit of a ceremony of the job.

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MT COMMENT HERE : I see what you mean. Obviously HM Ship certainly was (fast) moving. My only point of adressing this assumption here was under the following approach : if we are to reprocess to-day these historical data (through one method or the other), I do not see any other realistic option than "pretending" that all measures occured at the same time and from a non-moving vessel. From the published data, and for lack of more specific details, I cannot take any other "reasonable" assumption to carry out my computations, while at the same time I have to appreciate that my computation results might be "biased" due to this lack of all relevant data. Would you agree here ?

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Regarding the heights ... the only TWO reasonable assumptions here seem to be :

- either they are just corrected for sextant error (for the same reasons as here above, no possibility for a more "resonable" assumption) and in such case we have to process them as such,

- or they are unrefracted topocentric because, to the best of my knowldge - and thank you for any correction here - , that was the form (i.e. Body Center Unrefracted Topocentric) which was then required to carry out most conventional Lunar Clearings.

DOES ANYBODY KNOW whether these heights are simply "corrected for Sextant error" or whether they have already been 'pre-processed' into "Body Center Unrefracted Topocentric" heights ?

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"These are common printers' dagger symbols, that refer to a footnote
somewhere, on another page. Perhaps Kermit may find it helpful to compare
with the publicly-available text for the third voyage, which may offer an
analogy, on this matter and perhaps on others..

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OK, Good Idea. I will look it up and let our NavList Community know about my findings, unless meanwhile some sharp shooter has found the meaning of these dagger symbols ...

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For stars (I don't think lunar distances to planets were predicted until a
later era), except very close to exact full moon, it should be rather easy
to work it out. A planetarium program might be useful here (and elsewhere).
What's needed is to know whether it's before, or after, full Moon, and
whether the star was East or West of the Moon, which the almanac always
made clear.

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Yes good idea, anyway researching which Limb was used is not a tremendous task. As an example, I would think that the very first observation with Antares was with the Moon's FAR Limb.

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Thank you also for your insight of the Time variable used then, i.e. Greenwhich Apparent Time, instead of Mean Time as nowadays. ( + the 12 hour correction of course).

If we want to "reprocess these data" the ancient way, YES we need to use GAT.

On the other hand we can as well just reprocess all these data through modern computation methods, and then compare Longitudes, or even full positions.

Thank you also for the interesting information on the Longitudes Cyclic "worldwide" monthly (or so) oscillations. It is good to know.

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Thank you again and

Best Regards

Antoine M. "Kermit" Couëtte
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