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
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
