Next message: Alexandre E Eremenko: "Re: Timing Lunars with a Rock"
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
