Frank, Geoff, Thank you for the comment and the appreciation concerning the page about the Prague clock on my website.
It is very likely that the clock work is designed to indicate the mean solar time. In a source - I don't find it no more - I found that someone was charged with the task of fixing by hand the clock regularly on solar time with the help of a sundial. The clock work provided a good indication between two adjustments. This was especially necessary for a right indication of Bohemian and unequal hours. Measurement of Bohemian and Unequal hours depends on the time of sunrise and sunset. They are symmetrical in relation to real noon and asymmetrical in relation to noon in mean solar time. Since the symmetrical layout of the indication of this hours on the Prague clock a correct reading can only with the clock set to true solar time. I found the name of the astronomer in charge of the scientific maintenance of the Prague clock on this moment. I asked him for clarification and wait for his answer. Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 28-feb-2011, om 12:32 heeft The Thurstons het volgende geschreven: > Willy, > > Thank you for starting this interesting discussion and for directing us to > your website with its marvellous coverage of the Prague clock. It prompted me > to consult Henry King's book entitled "Geared to the Stars" which deals among > other things with astronomical clocks. He seems to have thoroughly > investigated the mechanism of the Prague clock and here is what he wrote in > 1978 about the clockwork as it was in 1865: > > "The horizontal input arbor ended in a long lantern pinion of 24 teeth. This > rotated 15.25 times in 24 hours and meshed with three concentric wheels 1.14m > in diameter and provided with 365 teeth(zodiac), 366(sun) and 379(moon). In > 24 mean solar hours, 24x61/4 or 366 teeth of the pinion rotated the sun-wheel > once while the zodiac-wheel advanced one tooth and the moon wheel slipped > back 13 teeth." > > He continues as follows: > > "The three large concentric wheels...........still form part of the dialwork, > but they are no longer turned by a simple pinion and the moon-wheel has a > correcting mechanism added by Boehm in 1865." > > This suggests to me that the original clockwork turned the sun-wheel at a > regular rate to match the mean sun and there is no record of a subsequent > equation of time modification since I find it hard to believe that such a > modification would have escaped the notice of Henry King. This evidence makes > me think that Frank King is correct in his guess. > > Geoff Thurston > From: [email protected] [mailto:[email protected]] On > Behalf Of Frank King > Sent: 28 February 2011 07:54 > To: Willy Leenders > Cc: Sundial sundiallist > Subject: Re: A blunder on the astronomical clock in Prague > > Dear Willy, > > I am not very familiar with the Prague > clock and I am confused by the recent > messages. You say: > > ... the clock indicates now Central > European Time rather than solar time > as it once was... > > This suggests something far more radical > than simply setting the clock for the > wrong longitude to keep the tourists happy. > > If I interpret you literally, you seem to > be saying two conflicting things about > the mechanism at the heart of the clock: > > NOW: the clock indicates Central > European Time - this suggests > exactly 24 common hours each day > (albeit set for the wrong longitude). > > IN FORMER TIMES: the clock indicated > local sun time - this suggests that > there were NOT exactly 24 common hours > each day because sun time is not quite > in step with common hours. > > QUESTION > > Did the clock really indicate local sun > time before it was adapted to keep tourists > happy? > > If the answer is yes, that means the clock > mechanism used to take account of the Equation > of Time AND that this mechanism has now been > disconnected. Can this be true? > > My guess is that the clock used to indicate > local MEAN sun time but I should like to have > that guess confirmed or rejected! > > Frank H. King > Cambridge, UK > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1204 / Virus Database: 1435/3471 - Release Date: 02/27/11 >
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