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    Lord Kelvin's lunars game (and an old joke)
    From: Frank Reed CT
    Date: 2005 May 26, 22:41 EDT

    In 1908, shortly after the death of the famous  classical physicist Lord
    Kelvin (William Thomson), "The Observatory" published a  note on a little game
    involving longitude by lunar distance observations which  Kelvin had proposed for
    a math competition at Cambridge in 1874. The challenge  he proposed was:
    "  Describe the method of 'lunars' for finding  longitude at sea, explaining
    the use of each of the observations to be made, and  the character of the
    tabular data required. Why is this method rarely used in  modern navigation?
    Show how a castaway in the N. hemisphere could, on  any clear night, with no
    other instrumental appliances than a piece of small  cord, determine his
    latitude approximately, and on moonlight nights, with  favourable stars, his
    longitude, if he has a Nautical Almanac. Estimate limits  of error for each
    determination."
    
    Which was followed by an early version  of an old joke:
    "  One of the other examiners remembers that on this  unusual type of
    question coming before the board, the following solution was  suggested: --Hang up
    the Nautical Almanac by the cord, determine the time of its  swing as a
    pendulum, and hence find the force of gravity; and then find the  latitude from the
    formula connecting it with gravity."
    
    -FER
    42.0N  87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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