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    Coordinates on Cook's maps
    From: Alexandre Eremenko
    Date: 2007 Apr 15, 10:40 -0700

    I used photocopies of the original maps of
    Cook's expedition published by Hakluyt Soc.
    by Cambridge University Press
    in 1955 (Available at Purdue library).
    There are 68 maps and shore views,
    and the collection is claimed to be complete.
    Only the following maps have the right scale and
    coordinates on the sides, with longitude from Greenwitch,
    to determine positions
    of certain points with 1' accuracy.
    
    I choose a conspicious point on a map,
    usually a cape, take its coordinates from the map,
    and then try to identify the same point on
    Terraserver photos. The results are rounded to 1 minute.
    First error is in latitude, second in longitude.
    
    First voyage (no chronometers were available):
    
    Chart 9.  Cook's coords:      16d40'S 151d29'W
              Terraserver:        16d41'S 151d32'W Er:-1', -3'
    Chart 13. East Cape: 37d43'S 179d0'E,
              Terraserver:        37d41'  178d33'  Er:+2', +27'
              Table Cape:         39d07'  178d25'
              Terraserver:        39d12'  178d00'  Er:-5', +25'
    Chart 18. Cape Teerawitte:    42d21'S 175d35'E
              Terraserver:        41d18'  174d42'  Er:+3', +53'
              Cape Campbel:       41d41'  175d13'
              Terraserver:        41d47'  174d20'  Er:-6', +53'
    Chart 24. Cape York:          10d42'S 141d42'E
              Terraserver:        10d43'  142d36'  Er:-1', -54'
    
    
    Second and third voyages (both chronometers and Lunars used):
    
    Chart 35. Friendly Islands:   21d16'S 174d44'E
              Terraserver:        21d17'  174d55'  Er:-1', -11'
    Chart 55. N point Hawaii isl: 20d17'N 156d00'W
              Terraserver:        20d16'  155d52'  Er:+1',  +8'
              Karakakooa bay:     19d28'N 156d00'
              Terraserver:        19d28'N 155d56'  Er:-0',  +4'
    Chart 57. Aivatcvhka bay:     52d54'N 157d33'E
              Terraserver:        52d56'  158d28'  Er:-2',  -45'
              Another point there:52d51'  157d48'
    
    Second and third voyages (both chronometers and Lunars used):
    
    Chart 35. Friendly Islands:   21d16'S 174d44'E
              Terraserver:        21d17'  174d55'  Er:-1', -11'
    Chart 55. N point Hawaii isl: 20d17'N 156d00'W
              Terraserver:        20d16'  155d52'  Er:+1',  +8'
              Karakakooa bay:     19d28'N 156d00'
              Terraserver:        19d28'N 155d56'  Er:-0',  +4'
    Chart 57. Aivatcvhka bay:     52d54'N 157d33'E
              Terraserver:        52d56'  158d28'  Er:-2',  -45'
              Another point there:52d51'  157d48'
              Terraserver:        52d53'  158d42'  Er:-2',  -54'
    
    The average absolute error in latitude is 2.3'.
    The average absolute error in longitude is 33' (36' in
    the first voyage).
    This corresponds to a Lunar distance measurement
    accuracy of about 1', approximately.
    
    I may conclude that the measurement accuracy was
    about 1', and extra 1' in latitudes comes from
    the horizon (or perhaps they used wood quadrants
    instead of metal sextants for
    altitudes, as Norrie advises:-)
    
    The log of astronomical observations shows that enormous
    number of measurements was made for each Lunar,
    with 3 or 4 sextants and different observers.
    It seems that to determine longitudes of important points
    on the shore they made around 100 measurements altogether
    for each such point.
    
    It is interesting to find out how much of these
    errors is due to the almanac errors.
    
    Alex.
    
    
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