 Check out the bookstore at IRBS.com |
|
|
|
|||||
|
||||||
From: Frank R (no email)
Date: Fri Apr 08 2005 - 18:10:44 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.
And:
"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.
-FER
_www.HistoricalAtlas.com/lunars_ (http://www.HistoricalAtlas.com/lunars)
|