RE: The Housewife's Trick
I think I remember hearing that one of the two horizontal dials at Erddig (near Wrexham, North Wales - the sundial nearer the house) was loose on its pedestal and that members of the Yorke family rotated it twice yearly during the twentieth century to allow for Summer Time. Can anyone confirm this? Andrew James PRI Limited, PRI House, Moorside Road Winchester, Hampshire SO23 7RX United Kingdom Tel: +44 (0) 1962 840048 Fax: +44 (0) 1962 841046 www.pri.co.uk PRI Limited is a company registered in England and Wales with company number 2199653 The Intelligent Metering Company This correspondence is confidential and is solely for the intended recipient(s).If you are not the intended recipient, you must not use, disclose, copy, distribute or retain this message or any part of it. If you are not the intended recipient please delete this correspondence from your system and notify the sender immediately. This message has been scanned for viruses by MailControl. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The Housewife's Trick
Chris, I did a fairly extensive analysis of The Housewife's Trick in "Herbert's Correction", The Compendium, June 1998, 5(2):24-27. Fred Sawyer - Original Message - From: Chris Lusby Taylor To: Sundial List Sent: Sunday, January 21, 2007 8:52 PM Subject: The Housewife's Trick In his wonderful book on sundials, AP Herbert referred to "The Housewife's Trick" of turning a sundial to correct for the Equation of Time. He seemed to be suggesting that it was a well-known trick - take your horizontal sundial, turn it to agree with a watch and it will continue to tell better time than it would if aligned due north-south. He was, of course, writing in England. This trick would not work well much nearer the equator. Has anyone any evidence that housewives do this? Has anyone investigated whether it works? I have in the back of my mind that I've seen it analysed somewhere but I forget where. Anyway, I've just looked into it, as I've been trying to invent a universal sundial base that would allow any sundial mounted on it to be adjusted for the Equation of Time. Before making something theoretically correct, I thought it might be worth seeing if the "housewife's trick" is actually good enough. (Those of you who know me are probably horrified but, hey, I'm an engineer.) I examined two versions of the trick: turn the dial and gnomon together or turn just the dial, leaving the gnomon unmoved. If you turn just the dial the effect is to leave the shadow unmoved, but to move the hour lines. Apart from the minor problem that the hour lines normally radiate from two different points on either side of the gnomon, the effect of turning the dial is independent of the sun's declination, so easy to calculate. For my latitude (51 degrees) it isn't at all bad! It can reduce the difference between sun time and clock time to less than 3 minutes, and, typically, less than 1 minute throughout the day. If you turn the dial and gnomon together, the effect on the dial's timekeeping is a complicated function of the sun's declination and time of day. But the result seems to be even better, typically less than a minute error except when the sun is very low in the sky. (These are my preliminary, unchecked, theoretical results. I may be wrong. It wouldn't be the first time.) Luckily for us in the northern hemisphere, the trick works better here than in the southern hemisphere as it works poorly in summer, but the EoT is small then. So I'm inclined to forget about making a polar axis EoT base for sundials and just use the housewife's trick. It should be easy to make a turntable to mount a sundial and to mark on it the rotation needed for any date. Thank you APH. Chris Lusby Taylor 51.4N 1.3W .. -- --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
The Housewife's Trick
In his wonderful book on sundials, AP Herbert referred to "The Housewife's Trick" of turning a sundial to correct for the Equation of Time. He seemed to be suggesting that it was a well-known trick - take your horizontal sundial, turn it to agree with a watch and it will continue to tell better time than it would if aligned due north-south. He was, of course, writing in England. This trick would not work well much nearer the equator. Has anyone any evidence that housewives do this? Has anyone investigated whether it works? I have in the back of my mind that I've seen it analysed somewhere but I forget where. Anyway, I've just looked into it, as I've been trying to invent a universal sundial base that would allow any sundial mounted on it to be adjusted for the Equation of Time. Before making something theoretically correct, I thought it might be worth seeing if the "housewife's trick" is actually good enough. (Those of you who know me are probably horrified but, hey, I'm an engineer.) I examined two versions of the trick: turn the dial and gnomon together or turn just the dial, leaving the gnomon unmoved. If you turn just the dial the effect is to leave the shadow unmoved, but to move the hour lines. Apart from the minor problem that the hour lines normally radiate from two different points on either side of the gnomon, the effect of turning the dial is independent of the sun's declination, so easy to calculate. For my latitude (51 degrees) it isn't at all bad! It can reduce the difference between sun time and clock time to less than 3 minutes, and, typically, less than 1 minute throughout the day. If you turn the dial and gnomon together, the effect on the dial's timekeeping is a complicated function of the sun's declination and time of day. But the result seems to be even better, typically less than a minute error except when the sun is very low in the sky. (These are my preliminary, unchecked, theoretical results. I may be wrong. It wouldn't be the first time.) Luckily for us in the northern hemisphere, the trick works better here than in the southern hemisphere as it works poorly in summer, but the EoT is small then. So I'm inclined to forget about making a polar axis EoT base for sundials and just use the housewife's trick. It should be easy to make a turntable to mount a sundial and to mark on it the rotation needed for any date. Thank you APH. Chris Lusby Taylor 51.4N 1.3W ..--- https://lists.uni-koeln.de/mailman/listinfo/sundial