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    Re: Lunars in 1766
    From: George Huxtable
    Date: 2004 Oct 2, 09:27 +0100

    Some comments on Alex Eremenko's recent posting about Bougainville's
    circumnavigation.
    
    
    
    He write-
    >The (Russian) book I have and the log translation you have
    >seem to be two different books.
    >My one is a translation of the book published in Paris
    >in 1771, 2 years after the completion of the voyage,
    >and this is definitely NOT a log book. It does not contain daily records.
    >It is just a narrative.
    
    The document that the Hakluyt society translated is rather more than a log
    book, though it does include the daily entries from the log. The word
    "journal" describes it best.
    
    Bougainville's "Voyage autour do monde par la fr?gate du Roi La
    Boudeuse...."  was published in Paris in 1771, and a second edition in 2
    vols in 1772. There's a modern edition in French, "Voyage autour du monde",
    edited by Bideaux and Faessel, Paris, 2001. There's also a book by E
    Taillemite, "Bougainville et ses compagnons autour du monde 1766-1769, in 2
    vols, Paris 1977. I have seen none of these.
    
    >Still earlier in the book he mentions more details about the events
    >on November 27:
    >
    >"...Only on November 27 approximately on Lat 47, when according to
    >our DR we were in 35 leagues from Patagonie, the measurement
    >showed the depth of 70 sazhens [I don't know what unit he uses.
    >It is translated by the Russian word "sazhen". My Russian-English
    >dictionary
    >translates this as "Russian fathom (1.83 meters)"-A.E.]
    >with mud and fine grey and black sand on the floor.
    >Since then we always encountered this ground at the depths
    >67, 60, 55, 50, 47 and finally 40 sazhens until the moment when we saw
    >the land and this was the cape of Vierges.
    
    The Russian "sazhen", if it's 1.83 meters, corresponds exactly to the
    English "fathom". It sounds like someone's best shot at transcribing the
    sound of the word. I think the French equivalent name would be the
    "brasse". All this was before the days of the French revolution and the
    metric system.
    
    The Hakluyt edition has the same information about the soundings, but as
    part of the daily entries from the log. The information in the Russian
    version seems to have been collected together and condensed in an
    abridgment process.
    
    In the late 1700s, unauthorised "pirate" copies and abridgments of popular
    works were rather common, and it may be that the Russian translation was
    made from one of these.
    
    >I did not want to approach the shore too closely, until I reached
    >parallel 49d because I was afraid of a lone rock which I saw in 1765 on
    >the parallel 48d34' S, 6-7 leagues from the shore.
    >I noticed it in the morning at the same moment when we saw the land.
    >The weather was perfect and I could measure our lattitude precisely
    >at noon. [Apparently he refers to 52d mentioned above on Dec 2-A.E.].
    >We passed only 1/4 of a league from this rock.
    
    All this stuff about the rock is missing from the Hakluyt volume, which is
    something of a surprise.
    
    By the way, my 5-vol "Times" atlas of the 1950s shows no hint of any such
    rock or shallowing in that position, which would indeed have been a great
    danger to navigation. If anyone has a sea-chart showing the Patagonian
    coast of Argentina, it would be interesting to learn if such a rock
    appears, or whether Bougainville "imagined" it.
    
    [When Cape Vierges was
    >noticed.
    >Then he describes birds, which I skip.-A.E.]
    
    I can't find the stuff about birds, either. Perhaps Dunmore has made his
    own abridgments, though he doesn't seem to admit to it. It might be
    productive for anyone interested to check his Hakluyt volume against
    Bougainville's 1771 text.
    
    Dunmore also includes journals of some of the personnel on board, but in
    that case he clearly states that these are extracts, covering the Pacific
    regions. He omits the stuff around South America, our present interest.
    
    >I conjecture that the translator was not understanding the text
    >he was translating, not speaking of the numerical data which were
    >probably never carefully proofread. In fact the Russian translator
    >complains
    >in his introduction that "the book is overloaded with details about
    >navigation":-)
    
    This was a common problem, which remains, to a large extent, to this day.
    Translators and editors are selected for their knowledge of the language or
    the geography, not the navigation. Even if a present-day navigator advises,
    he is unlikely to be familiar with the early methods such as lunars.
    
    >BTW, I read the description of the Hadley octant in the book by
    >Norie (1828). It had a veriner permitting to
    >read the angles only to the whole minutes.
    
    Yes, that was common. I recommend you look at listmember Peter Ifland's
    superb book "Taking the Stars", with its many pictures and explanations of
    instruments, ancient and modern.
    
    >So it is not clear to me why Bougainville includes meaningless
    >seconds to his longitude recordings.
    >He did understand the accuracy of his measurements, did not he?
    
    Well, as soon as you start averaging a number of observations, each
    recorded to the nearest minute, you have a problem. How do you denote the
    fractional-minute that results?
    Today we would simply put in a decimal point and use tenths of a minute,
    which accords with the precision of the almanac predictions. The
    conventions of Bougainville's time were that fractions of a minute were
    always denoted in seconds. It didn't imply that in angles given to seconds,
    the individual seconds themselves were meaningful.
    
    The navigator's correction procedures, such as refraction tables, used
    quantities given in minutes and seconds, and so navigators would, from the
    start, work in seconds. It made some sense, of course, to work the
    corrections to a higher level of accuracy than the observations, to prevent
    accumulation of errors, and then if necessary do any "rounding" right at
    the end.
    
    But little of an navigator's work called for the precision of arc-seconds.
    It was just the next unit-of-division after minutes, one of the many
    unfortunate consequences of the sexagesimal system that was imposed on us
    by the Babylonians and Greeks, and has plagued navigators ever since.
    
    I have seen lunar calculations from the early 1800s in which the navigator
    has gone to the absurd lengths of doing his intermediate working to tenths
    of an arc-second.
    
    Certainly, there was no point in Bougainville, or any other navigator,
    quoting his lunar longitudes to the arc-second, when the likely inaccuracy
    amounted to many arc-minutes.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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