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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Timing Lunars with a Rock
From: Frank Reed CT
Date: 2005 Jul 17, 21:23 EDT
From: Frank Reed CT
Date: 2005 Jul 17, 21:23 EDT
Here's a nice trick. A rock on a string and an assistant with a bag of pebbles will make do for a clock for timing the separate sights involved in a lunar observation. The details: " Pendulum.--A Traveller, when the last of his watches breaks down, has no need to be disheartened from going on with his longitudinal observations, especially if he observes occulations and eclipses. The object of a watch is to tell the number of seconds that elapse between the instant of occulation, eclipse, etc., and the instant, a minute or two later, when the sextant observation for time is made. All that a watch actually does is to beat seconds, and to record the number of beats. Now, a string and stone, swung as a pendulum, will beat time; and a native who is taught to throw a pebble into a bag at each beat, will record it; and, for operations that do not occupy much time, he will be as good as a watch. The rate of the pendulum may be determined by taking two sets of observations, with three or four minutes' interval between them; and, if the distance from the point of suspension to the centre of the stone be thirty-nine inches, and if the string be thin and the stone very heavy, it will beat seconds very nearly indeed. The observations upon which the longitude of the East African lakes depended, after Captain Speke's first journey to them, were lunars, timed with a string and a stone, in default of a watch." --From "The Art of Travel: Shifts and Contrivances Available in Wild Countries" by Francis Galton, London, 1872. (google it if you want to read it. lots of other interesting suggestions) -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars