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    Theodilite Shots by Day
    From: Peter Fogg
    Date: 2002 Feb 4, 12:41 +1100

    Explorers of the Antarctic, such as Douglas Mawson in the early years of
    the last century, used a theodolite (or something similar) as their
    principal method for fixing their position using sun sights and for
    aligning their compass (which was close to useless so near to the South
    Magnetic Pole).
    
    In summer, weather permitting (his book was called 'The Home of the
    Blizzard') the sun was just above the horizon and circled it in endless
    day. When its azimuth was at 90� or 270� the resulting line of position
    would give them a longitude and at 360� or 180� they could obtain a
    latitude. In practice, like the rest of us, they took sights when
    weather permitted, and used ded. reckoning to fill in the gaps. It must
    have worked, navigating their way back to base camp seems to have been
    the least of their problems, and they produced accurate maps.
    
    By way of contrast, various intrepid souls insisted on crossing from
    British India into Tibet, particularly during the latter half of the
    19th century, as if its blank expanses (on their maps) were an affront.
    The Tibetans wished to be left in peace and would expel them when they
    were found so they went disguised, often as Hindu pilgrims. An intrument
    on a tripod was a teeny bit suspicious so their main tool was the prayer
    wheel, still widely used in Tibet. Its a bit like a child's rattle, held
    in one hand, a weight on a string spins a cylinder which is inscribed
    with a prayer and thus mechanically propelled, hopefully earning much
    merit. The pundit's version was calibrated to assist them to record the
    distances covered at a set pace with paper, pencil, and notes kept
    inside. A sextant was useful in secluded places, not just for fixing a
    position but also for calculating heights and distances - its mostly up
    and down country.
    
    
    

       
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