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    Re: Thomas Jefferson and Lunar Obs.
    From: Frank Reed
    Date: 2005 Apr 8, 18:10 EDT
    George H wrote:
    "I don't recall seeing any accounts of travellers being assisted by the
    observatory after their return, to correct lunar-based or Jupiter-based
    longitudes for errors in prediction. That's not to say it didn't happen,
    and I would welcome any references to it, if it did."
    Remember, a few weeks ago, George, when Matthew Flinders' cat came up in discussion??
    I followed up with his words on this very topic of correcting observed lunar longitudes with Greenwich observations... You even commented on the post as follows:
    "Frank's quote from Flinders about after-the-event correction of longitudes
    is indeed of great interest."
    But to save looking through the archives, here's the relevant passage again:
       "The publication in 1814 of a voyage commenced in 1801, and of which all
    the essential parts were concluded within three years, requires some
    explanation. Shipwreck and a long imprisonment prevented my arrival in England until
    the latter end of 1810; much had then been done to forward the account, and
    the charts in particular were nearly prepared for the engraver; but it was
    desirable that the astronomical observations, upon which so much depended,
    should undergo a recalculation, and the lunar distances have the advantage of
    being compared with the observations made at the same time at Greenwich; and in
    July 1811 the necessary authority was obtained from the Board of Longitude. A
    considerable delay hence arose, and it was prolonged by the Greenwich
    observations being found to differ so much from the calculated places of the sun and
    moon, given in the Nautical Almanacks of 1801, 2 and 3, as to make
    considerable alterations in the longitudes of places settled during the voyage; and a
    reconstruction of all the charts becoming hence indispensable to accuracy, I
    wished also to employ in it corrections of another kind, which before had been
     adopted only in some particular instances."
       --Matthew Flinders, 1814.
    Note that Flinders was correcting observations taken just a few years before the Lewis & Clark expedition.
    And George wrote:
    "One difficulty arises from the English weather. Not only did the sky have
    to provide a clear view of the Moon, at the moment of local transit for the
    traveller, but to obtain a time correction from Greenwich, the sky would
    also have to be clear, at the moment of that transit, at the observatory."
    The discrepancy between the almanac data and the Moon's actual position appears to be rather slowly changing, over the course of a few days, so one observatory would probably suffice. Of course, you could always build two. The instruments required are specialized, but not impossibly expensive even for the young USA.
    And wrote:
    "Another difficulty arises from international politics of the time. Would
    American travellers, departing in 1803, be able to rely with confidence on
    future cooperation from the British Commissioners of Longitude?"
    I agree. It would have been reckless to depend on the political situation hence a local US observatory would have been much better. William Dunbar himself had a nice observatory down among the bayous of Louisiana back then.
    "I understand that available in America at that time was a local edition of
    the Nautical Almanac, and I would be interested to learn whether this was
    produced by agreement with the Board of Longitude, or whether it was a
    pirated copy."
    There were several by Blunt, Garnett, Patten published in America between about 1802 and 1855 (the latter date is when the "American Nautical Almanac" became available, as a subset of the "American Ephemeris & Nautical Almanac"). I've never seen the early American re-publications refered to as pirated in the same sense that Moore had been pirated by Blunt, for example. It does not appear that the UK Board of Longitude claimed any form of copyright over the data in the Nautical Almanac despite the fact that the data could potentially be used by an enemy. It would have been difficult to sustain international cooperation over the development of the science of navigation if the results were treated as proprietary.
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