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Bill Noyce, you wrote:
"Was that caused by the mix-up with leap year, that Nathaniel Bowditch
made such a big deal about?
Even though 1800 is divisible by four, it wasn't a leap year."

I've been meaning to mention that the "almanac errors" we've been talking
about are not errors, as in mistakes, but inaccuracies in the model of the
Moon's motion. As theory improved and observational data accumulated, the
ability to predict the Moon's position has gotten better and better. In
1803, the position was off by 30 arcseconds on average (in terms of the
absolute error in lunar distances). These were not mistakes. That was simply
the best they could do with the science then available. These almanac
"errors" only affected the "longitude by lunars". Jusr a dozen years later
the inaccuracy had been reduced to about 7 arseconds on average. By 1860, it
was down to 3 arcseconds.

The leap year problem that Bowditch and others noticed was in editions of
Moore's "New Practical Navigator" from the 1790s. This was an actual mistake
 --Moore should not have listed 1800 as a leap year. It was fixed by 1800,
both in Moore and in Bowditch's edited version of Moore, which eventually
became the "New American Practical Navigator", so the only navigators
affected by this error were those who were using an older edition of Moore.
It caused a real error in the Sun's declination and therefore the latitude
by Noon Sun which was a primary method of navigation for the vast majority
of vessels in that period. It was said back then that some vessels were lost
because of this error in Moore's Navigator. I think that may be more legend
than reality --and it didn't hurt sales of Bowditch's revised book to repeat
the story in any case!

 -FER

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