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George H you wrote:
"It seems that the  British almanac had become unduly complacent, and had
just kept on churning  out lunar distance predictions that were no better
than those that had been  supplied to Cook by Maskelyne, 90 years earlier,
in spite of the advances in  astronomy that had taken place in the meantime."

There's a little more to  it than that. The tables for the Moon were improved
several times from 1767 up  through 1808 or so. By that date the lunar
distance tables were very good with  errors typically as small as 6 to 12 seconds of
arc. But after that, they  stopped improving and began a slow decline. The
British Nautical Almanac  calculators continued to use tables (Burckhardt's, I
think) prepared way back in  1808 decades later. The predictions of the tables
became steadily worse (I  haven't investigated yet whether this decrease in
accuracy was happening  linearly with time or perhaps quadratically). This must
have contributed to some  extent to the declining use of lunars... but perhaps
it was also a result of  that decline.

And:
"Chauvenet is emphatic, in 1868,  about  the
importance of this matter for US Navy vessels."

He's emphatic, but  he was a bit of a voice in the wilderness. It would be
interesting to know how  many US Navy navigators ever got around to shooting
lunars and reducing them via  Chauvenet's method. By this date it seems that
lunars had already become what  they are again today --a good challenge and a test
of a skilled  navigator.

-FER
42.0N 87.7W, or 41.4N  72.1W.
www.HistoricalAtlas.com/lunars

   

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