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