Re: azimuth lines
Hi Frank et al, Dials with azimuth lines are rare but not unknown in the UK. Writing from memory, there is a rather nice one on Grundisburgh church near me and I believe the famous Queens' College, Cambridge, dial also has them amongst all the other furniture. There are a few others, I'm sure: didn't Ian Butson restore a wooden one? The key requirement, of course, is that there has to be a nodus so the gnomon on your lighthouse dial can't be original. The dial is in obvious need of restoration, or at least conservation. Perhaps a nodus could be added. Once the spacings of the azimuth lines have been measured, the trig to calculate the nodus position is straigntforwrad. Regards, John D -- Dr J Davis Flowton Dials From: Frank Evans To: Sundial Sent: Thursday, 1 August 2013, 14:03 Subject: azimuth lines Greetings, fellow dialists, Attached is a picture of the dial on a lighthouse in North Shields, England (55N 1.5W). It is probably from the eighteenth century and is badly eroded. As well as its hour marks it has a series of vertical azimuth lines labelled with the points of the compass. These may lie between the solstice curves. I am at a loss as to how the lines would have worked. There is no sign of a nodus on the gnomon (which looks old). Possibly, if there was a date scale associated with the azimuth lines, now eroded away, then it would be possible to get the sun's bearing from where the time line crosses the azimuth line but that looks pretty cumbersome. Any suggestions? Frank 55N 1W --- https://lists.uni-koeln.de/mailman/listinfo/sundial--- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: azimuth lines
The Queens' College dial certainly has azimuth lines as John wrote. Frank, is it possible that some feature of the rather nice ornamental and unusual gnomon support provides the nodus? Working from the azimuth line spacing you should be able to estimate the required height of the nodus and see whether this is at all plausible. The "8" support looks too low down the dial really, but it may be worth a calculation if only to rule it out! Regards Andrew James Secure Meters (UK) Ltd. is a registered company in England: 2199653 Secure House, Moorside Road, Winchester, SO23 7RX This correspondence is confidential and 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. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Re azimuth lines
Hi Frank E, As Frank K has said, your suggestion for reading azimuths with a polar-oriented gnomon and a set of declination lines (rather than with a nodus) is perfectly possible. But, in my experience, it would make the dial somewhere between very rare and unique as all the English examples I've ever seen make (or made) use of a nodus. Apart from anything else, trying to read shadows and dec lines on a wall sundial taxes the eyesight and visual coordination. FK's wacky idea of a secondary, vertical, gnomon to indicate azimuth directly is fun. There are cases on horizontal dials (eg the Whitehouse dial in Cumbria) where this was done. But again, I've never seen it on a vertical. Any chance of the dial being conserved/restored? Regards, John - Dr J Davis Flowton Dials From: Frank Evans To: "King, Frank" ; "Davis, John" ; andrew.ja...@securetogether.co.uk; Sundial Sent: Friday, 2 August 2013, 20:36 Subject: Re azimuth lines Greetings, fellow dialists, Thanks to all for suggested solutions to my dial puzzle. As I read the dial picture, the azimuth lines related to the supposed nodus would have extended from the summer solstice curve, visible on the dial, up to a winter solstice curve now lost. If so this rules out the use of the figure 8 gnomon support as a nodus as its shadow in the picture falls outside this frame. Suggestions so far are that the gnomon is a replacement together with indications of how a new nodus might be calculated. I am still wondering about the alternative suggestion I made that there was no nodus but a vertical date scale at the sides. Then, selecting the date, you follow the declinational curve from there to the point where the gnomon shadow crosses the azimuth line and that gives the sun's bearing. Is this correct in principle and do any dials anywhere use this method? Frank 55N 1 W--- https://lists.uni-koeln.de/mailman/listinfo/sundial
