The equation of time was already known to Ptolemy! See Kevin Karney’s excellent article on this subject in the NASS compendium of December 2009.
Ptolemy’s equation of time was applied to heavenly bodies in general, particularly the moon, to explain differences in their return to the same place in the sky. The equation of time, as applied to the sun and the length of the day, was known early astronomers, although it remained a technical curiosity in the absence of accurate clocks. Tables of its value were published and refined by a number of astronomers, notably by John Flamsteed (1692), who clearly set out the two principal causes. Jack From: R Wall [mailto:[email protected]] Sent: Wednesday, June 22, 2011 7:46 PM To: Jack Aubert; 'Robert Terwilliger'; [email protected]; [email protected] Subject: Re: EoT diagram Hi Jack, Now that’s interesting. I didn’t know there was such a clock as a “Real-time-clock”. I did know that clock makers had included a small sundial with their clocks to allow the owner to adjust their clocks. To do that they must have had a copy of the Equation Of Time. Thanks very much for the information about the Real-Time-Clock. Roderick Wall. From: Jack Aubert <mailto:[email protected]> Sent: Thursday, June 23, 2011 9:17 AM To: 'R Wall' <mailto:[email protected]> ; 'Robert <mailto:[email protected]> Terwilliger' ; [email protected] ; [email protected] Subject: RE: EoT diagram By the late 17th century, as clocks became more accurate, clockmakers struggled with the fact that they did not seem to tell true (solar) time. The Mercure de France in 1738 reported that “Many clockmakers find themselves exposed to criticisms of their methods by those who claim that their clocks are not accurate, since they do not agree with everybody’s favorite neighborhood sundial.” Some attempts were made to force mechanical clocks to adapt to true time. The first true time clocks, designed by the English clockmaker Groton, appeared in London around 1692. William III gave one of them as a present to Charles II of Spain. Clockmakers presented papers to the French Royal Academy of Science on the subject. Several well known clockmakers continued to produce real time clocks: One of these is shown in this illustration http://truesundials.com/real-time-clock.gif from Diderot’s Encyclopedia. The mechanism included a kidney-piece cam for the equation, and a dial with two hands, one golden showing a sun for true time and another steel for mean time. Some of these clocks can be seen at the Conservatoire des Arts et Métiers in Paris. Jack From: [email protected] [mailto:[email protected]] On Behalf Of R Wall Sent: Tuesday, June 21, 2011 8:19 PM To: Robert Terwilliger; [email protected]; [email protected] Subject: Re: EoT diagram Hi Bob, If you have a look at the Jules Audemars Equation of Time watch movement in my link you will see a kidney piece. Roderick Wall. From: Robert <mailto:[email protected]> Terwilliger Sent: Wednesday, June 22, 2011 9:43 AM To: 'R Wall' <mailto:[email protected]> ; [email protected] ; [email protected] Subject: RE: EoT diagram Roderick, The eot watch your link produced does not seem to be mechanical – hence no kidney piece. Google movement equation of time watch Then try the images Here’s one http://www.breguet.com/var/ezwebin_site/storage/images/equation-of-time/3646-5-eng-GB/Equation-of-time.jpg Bob _____ From: R Wall [mailto:[email protected]] Sent: Tuesday, June 21, 2011 6:06 PM To: Robert Terwilliger; [email protected]; [email protected] Subject: Re: EoT diagram Hi again, This is a good link on EOT and watches http://www.timezone...com/extras/200711101492 <http://www.timezone.com/extras/200711101492> Roderick Wall. From: R Wall <mailto:[email protected]> Sent: Wednesday, June 22, 2011 7:08 AM To: Robert Terwilliger <mailto:[email protected]> ; [email protected] ; [email protected] Subject: Re: EoT diagram Hi all, After sending my last email. I thought I should have 1st searched the Internet before sending it: http://forums.timezone.com/index.php?t=tree <http://forums.timezone.com/index.php?t=tree&goto=5710449&rid=0> &goto=5710449&rid=0 Note: scroll down to the larger photo. Looks as if the outer EOT ring can be adjusted (turned) to have the current EOT month at the top 12 o’clock position. And there are other “sun” information, what I’m not sure. By the way ChiLan, I think your time scale is the wrong way around. “+” should be “-“ and “-“ should be “+”. Roderick Wall. From: R Wall <mailto:[email protected]> Sent: Wednesday, June 22, 2011 6:18 AM To: Robert Terwilliger <mailto:[email protected]> ; [email protected] ; [email protected] Subject: Re: EoT diagram Hi ChiLian and Robert, Thanks ChiLan, your EOT curve is interesting. I suppose anything to do with sundials has a high chance of being invented before as sundials have been around for a long time. Robert, the kidney shape cam in the watch is interesting, is this watch still in production and can it be purchased. I’ve never seen a watch with EOT indication. Thanks, Roderick Wall. From: Robert Terwilliger <mailto:[email protected]> Sent: Wednesday, June 22, 2011 5:55 AM To: [email protected] ; [email protected] Subject: RE: EoT diagram The equation graph projected on a circle is used as a "kidney piece" cam in a watch movement that can indicate the equation. Here is a picture of the gear carrying the kidney piece. It turns once a year. http://people.timezone.com/mdisher/decorte/gyro2/gyro2_3.jpg Bob _____ From: [email protected] [mailto:[email protected]] On Behalf Of Chiu ?,Chi lian Sent: Tuesday, June 21, 2011 12:11 PM To: [email protected] Subject: EoT diagram Hi, I figured out a way to plot EoT curve which I didn't see in sundial books I own. Diagram is enclosed here. For a better resolution one, see http://dl.dropbox.com/u/31382133/EoT%20.png Best regards, ChiLian 24.8N 121E _____ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial _____ No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1382 / Virus Database: 1513/3716 - Release Date: 06/20/11 _____ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial _____ No virus found in this message. 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