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    Re: Precision of lunars
    From: Alexandre Eremenko
    Date: 2007 Apr 17, 13:59 -0400

    
    Dear George,
    I am glad that the three long messages
    I recently posted finally led to some feedback:-)
    (I already was beginning to think that this kind of posting
    is not of interest to the list members anymore.
    I am waiting for your opinion on Cook's maps.
    
    Let me make few minor comments on your message.
    
    > precisely-navigated balcony in the whole state of Illinois.
    
    Indiana.
    
    > In Navlist 2574, Alex quoted a favourite guru of mine,
    > Lord Kelvin,
    
    I would like to add that a whole volume of his collected
    papers is devoted to navigation. The volume I cited
    in my message. The company "Kelvin and Hughes" derives
    his name from the same person (which came as a big surprise
    to me). His most important inventions in the area
    of navigation, as I understand were a) a much better compass
    than models used in those days, b) a tide predicting machine
    and c) a deep sounding machine.
    His inventions and discoveries in other areas of physics
    mathematics and engineering are much more famous than these.
    
    > That lecture,
    > given in 1875 before he was Lord Kelvin,
    > as Sir William Thomson, shows the
    > sticking power of audiences and lecturers of those days.
    
    I doubt he actually delivered that whole lecture
    in one meeting:-)
    What is published as a "lecture" is sometimes a very expanded
    version of the actual speech.
    
    > In Kelvin's day the astronomical data had to come from
    > the nautical almanac,
    
    I suppose that when Kelvin was speaking of the limits
    of Lunars accuracy he meant the same as I mean:
    the accuracy of actual measurement of a distance.
    I believe that VERY precise reduction methods and
    "almanac data" were available to Kelvin (as they are
    available to me now), not limited to then existing
    Nautical Almanac. In the second half of XIX century,
    obtaining very precise data as well
    as very precise calculations
    did not constitude a problem in principle and could not
    influence the limit of the lunars accuracy.
    
    So I completely agree when you say:
    
    > It was all down to the skill of the observer,
    > and the precision
    > of his sextant, which was comparable
    > with the instruments of today.
    
    But I would be very interested in discussing the
    last part of this sentence. Where the best
    mid XIX century sextants
    better (or comparable, or wirth)
    than the best sextants available today?
    
    I have no definite opinion on this topic but have a lot
    of all sort of arguments and evidence in both directions.
    I can discuss some comparison results of my
    vernier C. Plath vs SNO, for example.
    
    Alex.
    
    
    
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