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Re: How was GMT originally established ?
From: Thomas Schmidt
Date: 2004 Jan 29, 01:04 +0100
From: Thomas Schmidt
Date: 2004 Jan 29, 01:04 +0100
Patrick Stanistreet wrote: > Just curious but when Harrison created his chronometers > there had to be some standard against which they were > set. Of course land based clocks were around but even > those clocks had to be set against some other standard. > I would guess that the ultimate standard at that time > would have been astronomical. Yes... > But still what exactly > was used to arrive at accuracy of a few seconds. > Was the land based authority setting GMT associated > with the Almanac office? At Harrison's time (17xx) there was no GMT (at least not in the sense of a zone or even universal time) and no associated authority. > Assuming timing of a star one ends up with a sidereal > clock but when did land based clocks achieve sufficient > accuracy to time a star over 24 or more hours so as > to differentiate between sidereal and solar time? Each observatory regularly observed the transits of the sun, corrected for the equation of time and compared the result with the observatory's clock. The clock was usually never reset in order not to disturb its mechanism which would otherwise move irregularly for a while afterwards. The corrections were mathematically added to subsequent clock readings which were thus calibrated to local mean time. It was also known how many seconds the clock gained or lost each day, so the correction could be interpolated accordingly. A good clock did not necessarily run at the correct rate, some error was allowed, but the error of a good clock had to be steady and predictable. I don't know too much about the history of clock accuracy, but my impression is that by the 18th or 19th century a competent astronomer with a good clock and a fresh set of clock corrections may have been able to time an event at the level of a fraction of a second, routinely at least at the level of seconds. I seem to remember dimly that Harrison observed the sun in order to calibrate his clocks, but I don't have a source handy. > Any book recommendations that cover this topic in detail? All of this has nothing to do with GMT in the sense of a standard time which was introduced in the late 1800s. If 'this topic' is the introduction of time zones and standard times, then this would probably be covered in the recent Clark Blaise Time Lord : Sir Sandford Fleming and the Creation of Standard Time Vintage, 2002 Bye, Thomas -- ------------------------------------------------------------------- Thomas Schmidt e-mail: schmidt@hoki.ibp.fhg.de