Frank Cheney
This quote is from the North American Sundial Society description of a sundial in the Old Rose Garden of the Botanical Garden University of California at Berkeley "The armillary dial is made of red bronze and rests on a quarried stone pedestal. The equatorial ring includes hour lines with 15-minute marks and Roman numerals. It was created by Frank Cheney, a UC Berkeley graduate, Class of 1941, and later donated to the Garden by his family. Mr. Cheney was a civil engineer who developed a hobby of building sundials" https://sundials.org/index.php/component/sundials/onedial/612 Probably the same person? Best wishes, Patrick Vyvyan <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Libre de virus.www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Sundial in walking stick
Rather curious to know what it makes finally, from what I can see it looks to be a modern novelty very similar to this one currently out of stock on the Internet https://www.alibaba.com/product-detail/Vintage-Brass-and-Wood-Sundial-Compass_1006081836.html Best wishes to all, Patrick Vyvyan On Sun, 2 Apr 2023 at 06:41, Peter Mayer wrote: > Hi, > > This walking stick with sundial, compass (and flask) is coming up for sale > at an Adelaide auction house. Bids are already above their modest estimate > of sale price. > > > best wishes, > > Peter > > -- > --- > Peter Mayer > Department of Politics & International Relations (POLIR) > School of Social Scienceshttp://www.arts.adelaide.edu.au/polis/ > The University of Adelaide, AUSTRALIA 5005 > Ph : +61 8 8313 5609 > Fax : +61 8 8313 3443 > e-mail: peter.ma...@adelaide.edu.au > CRICOS Provider Number 00123M > --- > > This email message is intended only for the addressee(s) > and contains information that may be confidential > and/or copyright. If you are not the intended recipient > please notify the sender by reply email > and immediately delete this email. > Use, disclosure or reproduction of this email by anyone > other than the intended recipient(s) is strictly prohibited. > No representation is made that this email or any attachment > are free of viruses. Virus scanning is recommended and is the > responsibility of the recipient. > --https://www.adelaide.edu.au/study/ > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: What's the inner scale on this photo for?
I'm afraid I can't give you any answers , but the original is in the Science Museum, London. They don't give any clues either, but I guess you could contact them https://collection.sciencemuseumgroup.org.uk/objects/co143/azimuth-sun-dial-simple-azimuth-sundial Best wishes, Patrick Vyvyan On Mon, 25 Oct 2021 at 14:23, Steve Lelievre < steve.lelievre.can...@gmail.com> wrote: > Hi, > > Today a website called Vermont Free Press published an appallingly > confusing (to me) summary of types of sundials. If you can bear to look, > it's at https://www.vermontpressbureau.com/types-of-sundials/ > > However, there was one thing about it that piqued my interest: the photo > of an azimuth sundial ( > https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg > ). > > From what I can make out, there is a metal flap at the end of the > alidade / sighting arm (the end at top in the photo). It must get turned > up to make a shadow-caster. I guess the arm has to be rotated so that > the shadow falls along it, and time is then read from where the > right-hand edge of the arm crosses the net of hour and declination > lines. But then, wouldn't the screws seen in the upper plate block the > arm from being turned to the required orientation? > > Another bit I can't figure is the little circular scale just north of > the centre of the dial, with the pointer. Perhaps just an Equation of > Time scale? Or perhaps a cam connects it to the arm so that it can be > used to set the arm's length? (The slot in the arm suggests it can be > slid in and out to set the tip at the applicable declination circle, > which is a nifty feature.) > > Cheers, > > Steve > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: What accuracy to aim for with a carefully made sundial?
A basic problem with the accuracy of sundials is the Analemma. Due to the tilt of the Earth, the position of the shadow for a given time moves in a "figure-of-eight" shape over the course of the year. Therefore, even if the sundial is very accurately marked and positioned, the shadow will only fall exactly on the hour line twice a year - the winter and summer solstices. The figure-of eight Analemma is quite often marked for midday (and can serve to give the date as well). On large sundials, the Analemma may also be marked for every hour - but on a smaller dial, this can be visually very confusing! Another solution, used on heliochronometers, is to allow the dial to rotate against a scale marked with the appropriate Analemma offsets according to the date. Best wishes, Patrick On Tue, 30 Jul 2019 at 14:40, wrote: > Hi Steve, > > as I built a large one (https://Kepleruhr.eu with 240m²) and thought some > about getting as accurate as possible here are my readings so far: > > 1) If you go for a sharp edge you will find out that the penumbra is all > the > times about 2 min in width which is the wandering time of all of the sun > diameter: The sun diameter is roughly 0.5° in the sky and it takes roughly > 2 > min for the sun to move this angle. The penumbra in angle does not depend > on > the distance from the gnomon to the face. So I would suggest that the > reading would be +/-2 min for untrained and about +/-1 min for trained > observers. This is valid for sundials using the bypassing shadow of the > Gnomon or the moving flare of any rectangle or circular iris. > > 2) I estimate a reading accuracy of the Kepleruhr by +/-15 sec (at high > noon > only): There is a wandering flare of 2 cm (+/- penumbra) with two side > edges > on a line of 2 cm which increases the reading accuracy. This wandering > flare > is produced by a spherical Nodus with this 2 cm gap southwards. There are > some movies at the concerning YouTube-channel (links given at the website). > > 3) In my case I made the calibration of the sundial by >a) calculate the hour and day line positioning by given parameters > (declination, geometry of gnomon, Nodus, wall) >b) erect the gnomon to the wall firstly without the painting >c) observe the shadow at one of the next fully sunny days - taking > series > of photos, calibrate them with respect to lens distortions, positioning, > etc >d) find the hourly shadow positions by machine vision techniques >e) adjust the above given parameter set as long as the total error of > deviations between the calculated and measured positions got a minimum >f) calculate the lines with the latest parameter set and do the > painting. >g) BINGO - it turned out (observing the sundial since years) that the > lines correctly follow the shadow on time. > > 4) I am on to build a sundial with a second reading of high noon - and did > do the concerning presentations (theory, fulfilled and planned > implementation steps) at sundial conferences in Austria. > > Good luck! > Kurt > > -Ursprüngliche Nachricht- > Von: sundial [mailto:sundial-boun...@uni-koeln.de] Im Auftrag von Steve > Lelievre > Gesendet: Dienstag, 30. Juli 2019 19:38 > An: Sundial List > Betreff: What accuracy to aim for with a carefully made sundial? > > Hello everyone, > > I'm planning to make a small vertical west dial, about 1m for the width of > the dial face, at my latitude of 49N. It will not use a nodus. > > The angular width of the sun makes it hard to get a really accurate time > reading, but there will also be small errors from mis-positioning of the > dial plate when installing (declination and inclination), imprecise > positioning of the gnomon or the hour lines, and perhaps other causes too. > > First, questions directed at those of you who have practical experience of > creating vertical sundials: If I'm careful and have a well-machined gnomon, > what level of accuracy might be achievable in practice? I assume > +/- 5 minutes throughout the day and year is fairly easy to achieve, but > what about +/- 2 minutes, or even +/- 1 minute? How well did you do? How > did > you measure your wall's declination? > > Second, have there been any studies of how well dial users compensate for a > penumbra - by which I mean gathering data from volunteers, studying the > spread of errors in time readings taken from a dial versus a reference time > source? (without employing a shadow sharpener) > > Thanks, > > Steve > > > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Wheatstone's polarizing sundial
Wheatstone's Polarizing Dial An explanation of Wheatstone's invention is to be found in the Report of the meeting of the British Association for the Advancement of Science in Swansea held in 1848, although to be honest it's scientific foundation has me a little challenged! The report is available online at https://www.biodiversitylibrary.org/item/46637#page/188/mode/1up Should you have access to an original paper copy, the description of the Polarizing Dial begins on page 10. The numeral scale represents one complete day of 24 hours - it seems the device can work even without direct sunlight. Best wishes, Patrick Vyvyan On Tue, 21 May 2019 at 16:07, Maes, F.W. wrote: > Recently the Tesseract Catalogue 109 was announced on this list. Item nr. > 13 is a polarizing sundial by Charles Wheatstone. A virtually identical > dial is in the collection of the Greenwich museums, see: > https://collections.rmg.co.uk/collections/objects/265579.html. > I have never understood how this sundial works. The hour scale shows 2 x > 12 hour numbers in a semicircle. So whatever pattern is observed in the > black glass reflector, it is obviously supposed to rotate over 180° in 24 > hours, which is half the angular velocity of the sun itself. How does this > frequency division-by-two come out? Can anybody explain? > > Thanks! > Frans Maes > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
short BBC video
Enjoyable short video 3 minutes, featuring Adrian Rodriguez Cozzani which may be of interest: https://www.bbc.com/reel/video/p074qwm6/the-guardian-of-the-sands-of-time --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Accuracy of wristwatch as compass
Dan, Using a watch seems too imprecise to give more than a general idea of the direction of North. However, the basic concept has been developed to provide precision solar compass instruments. In most cases these come with tables to correct latitude, date and local solar time. If you don't know it, you might enjoy a glance at Malcolm Barnfield's article *The Sundial goes to War * http://www.sundials.co.za/THE%20SUNDIAL%20GOES%20TO%20WAR%20web.pdf Best wishes, Patrick Vyvyan On Mon, 22 Oct 2018 at 14:09, fabio.sav...@nonvedolora.it < fabio.sav...@nonvedolora.it> wrote: > dear Dan > > the wristwatch as compass has 3 problems: > a) it shows the time of a different longitude, the one of the time-zone > (GMT or DST). > You should correct it for the local time but it is possible only if you > know your longitude. > > b) you should correct the time also for eot, it means you should start > with the local Sun time for the longitude where you'll use it. > > You can admit a little bit of imprecision avoiding a) and b), if your > longitude is not so far from the one of the time-zone. > > c) you have to rotate the watch around the 3-9 axes of the colatitude > angle, so you have to evaulate also your latitude. > > Overall it isn't a reliable way to find the north, it is useful to have > a rough estimate if you haven't other instruments. > > I have some 3D drawings for a book I'm writing, I attach 2 images, if > you wish I can send you, or anyone who request them, a more defined jpg. > > ciao Fabio > > -- > > Fabio Savian > fabio.sav...@nonvedolora.it > www.nonvedolora.eu > Paderno Dugnano, Milano, Italy > 45° 34' 9'' N, 9° 9' 54'' E, UTC +1 (DST +2) > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Dickens' sundial
Can't help with the current location, I'm afraid. But this link may be of interest to some https://www.bodleian.ox.ac.uk/johnson/jj-images/galleries/dickens It illustrates publicity for a commemorative version of Dickins' sundial made by Francis Barker and which copies the original commissioned by the writer. Best wishes, Patrick Vyvyan On 21 July 2018 at 04:21, Ian Maddocks wrote: > Hello Diallists > > > Whilst trawling Instagram #sundial i found this, asking for info about a > dial once belonging to Charles Dickens. Can anyone help them? > > There's a drawing and photo provided in the link below > > https://www.instagram.com/p/BldQFsbAixH/?tagged=sundial > > > Ian Maddocks > Chester, UK > 53°11'50"N 2°52'41"W > > > > > dickensmuseum <https://www.instagram.com/dickensmuseum/>The Missing > Sun-Dial > ** > The sun-dial stood 4ft 8in high, in the garden at Gad’s Hill (Dickens's > final home) in a most prominent position as it was considered one of > Dickens's most valuable treasures. > * > After Dickens’s death [in 1870], it was bought by Mr. Crighton, of > Rochester. Alice Morse Earle, in her 1902 book Sundials and Roses of > Yesterday, says that the dial was later sold in London for the sum of £50. > An article in the Pittsburg Press, 14 February 1899, gives more details > “There is offered for sale by a curiosity dealer in London the old sun-dial > and stone column formerly the property of Charles Dickens.’ In 1907 it was > exhibited in the ‘Pickwick exhibition’ in London, and had been lent by the > company Francis Barker sundial and barometer specialists, 12 Clerkenwell > Road, London. The company was also making replicas of the original to sell. > * > As we continue our search, let us know if you can shed any light on the > mysterious whereabouts of the sundial. > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Sundials in Belgrade / Novi Sad
Milutin Tadic has a site dedicated to sundials in former Yugoslavia: http://yusundials.com/category/old-yu-sundials/ There was also a recent project to install sundials in some 80 schools in Serbia. See: https://www.researchgate.net/publication/312305100_Sundials_as_Environmental_Posters Hope this is of interest, best wishes, Patrick *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 26 September 2017 at 03:42, Dan-George Uza wrote: > Hello, > > I will be travelling to Belgrade and Novi Sad next week. Can you recommend > a few sundials for me to visit there? Haven't found any on Sundial Atlas. > > Thanks > > Dan Uza > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Impact of making instruments out of boxwood
In the case of southern England, the principal source seems to have been Box Hill in Surrey, some 20 miles south of London - so, close enough to supply instrument makers (musical and scientific) in the capital. However the origins of the site are not clear. Some suggest medieval, others the 17th century. In the latter case, this would suggest the woodland was managed, presumably factoring in supply and demand. Best wishes to all, Patrick *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 7 September 2017 at 04:55, Patrick Powers wrote: > Hi John, > > Answer is I don’t know but it seems from the link below that all the > different varieties of box known at the time in Roman times were abundant. > If you can put up with the use of CE and BCE, see: > https://www.ebts.org/2013/12/boxwood-in-roman-times-by-mark-v-braimbridge/ > I expect that just as with oak (especially) but also with other tree > varieties in what is now Great Britain, the old forests were simply > over-harvested to their present state of relative rarity but that there was > never any real ‘national concern’ because there were always other sources > elsewhere. Indeed, by the thirteenth century it was as cheap to import oak > and fir (deal) from the Baltic as it was to bring it from anywhere in > Britain outside the home counties; presumably a symptom of the > extraordinary demand in London as well as of difficulties with overland > transport. > We also need to remember that the population of England in Tudor times was > only about 4 million, having risen from 2 million not long before, so > demand for things made of box would surely have been quite low. > Patrick > > > *From:* John Pickard > *Sent:* Thursday, September 07, 2017 2:25 AM > *To:* Sundial List > *Subject:* Impact of making instruments out of boxwood > > Good morning, > > This is purely a curiosity question. > > Box wood was favoured for rules and instruments for centuries when ivory > was > either too expensive or not available for some reason. Given the number of > rules etc. made from box wood, I would expect some contemporary concern > about the reduction in the number of trees available. > > My questions: > > 1. Where did all the box wood come from? > 2. Was there ever a shortage? > > > Cheers, John > > John Pickard > john.pick...@bigpond.com > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: How to save a sundial?
Yes, it should be possible. Wallpaintings have been removed from churches etc. The normal technique is to "stick" some sort of support to the front of the plaster to enable removal, then when it is fixed to a new back, this provisional support can be removed. Sounds simple, but there are many considerations including the nature of the paint and the plaster. There is some general information at https://en.wikipedia.org/wiki/Detachment_of_wall_paintings I would very definitely recommend seeking professional advice from a local museum, university etc with experience in this type of work. Best wishes, Patrick *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 24 August 2017 at 16:14, Dan-George Uza wrote: > Hello, > > There's a sundial on a ruined building which is going to be torn down > soon. We are trying to save it by removing the underlying plaster in one > piece. Can this be done? Any advice? > > Thanks, > > Dan Uza > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Barrington Court multi-face dial
Just in passing, the Barrington Court dial is clearly related to one in Old Westbury Gardens, New York, which were created in 1906. http://sundials.org/index.php/component/sundials/onedial/5 Perhaps the Westbury example is a copy, or given that the Barrington Court example appears not to have a very firm earlier provenance, perhaps both are late Victorian/Edwardian? I had a very quick glance at the Scottish chapter in The Book of Sun Dials by Mrs Alfred Gatty (1900 revised edition) but didn't see anything relevant. Best wishes to all, Patrick Vyvyan (also a bit of a radio ham, CD2PIH) *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 13 August 2017 at 04:35, John Foad wrote: > Many thanks for the offer, David, but I have a number of excellent photos > (in sunshine) from John from 2008. The Register says now (I have enhanced > it slightly since the 2015 edition, after reviewing all reports and the > photos): > > “Located on south lawn. Dodecahedron dial with pentagonal faces. Two > 'rows' of five dials. Top row reclines, bottom row inclines. All lines > and numerals visible, all gnomons intact and 4mm thick. Overall shows 4am > to 8pm in hours. The numerals are Arabic, and are in relief as is light > scroll work on at least some faces. Mounted 1760 mm high on a stone > pedestal. Surmounted by (weathered) lion rampant 460 mm tall. The dial is > said to have come from Scotland about 1910.” > > Nick Nicholls supplied a dimensioned drawing which I will attach to the > entry. > > Do we know Keith Brandt? Is it okay to send him the photos I have? If I > do, I will say they and the other info are for private study only and he > should refer back if he wants to publish. > > All the best, > > John > > > *From:* David Brown > *Sent:* Sunday, August 13, 2017 8:48 AM > *To:* John Davis > *Cc:* sundial > *Subject:* Re: Barrington Court multi-face dial > > Barrington Court is about 15 minutes by car away from where I live. If you > want detailed photos, I could get them for you. > Best wishes, > David Brown > Somerset, UK > > Sent from my iPad > > On 12 Aug 2017, at 09:56, John Davis wrote: > > Hi Keith, > > The Barrington Court dial appeared on the back cover of the September 2013 > *BSS > Bulletin* (vol. 25(iii)). The accompanying caption read: > > "The dodecahedron dial at Barrington Court (NT), Ilminster, Somerset. It > featured in the March 2013 issue and is seen here from the south, though > none of the dials faces exactly south. It is surprisingly small with the > actual polyhedron at not much more than head height. Recorded early in the > Society's history (SRN0040), it is in good condition and a nice example. > Photo: John Davis." > > The March 2013 article (by Peter Ransom) is really about an indoor dial > and does not provide much more detail of the polyhedral dial, other than > saying it has 5 reclining faces on the top row and 5 proclining ones in the > bottom row. I'm not sure if the BSS Register has more info. > > Regards, > > John > > > Dr J Davis > Flowton Dials http://www.flowton-dials.co.uk/ > BSS Editor http://sundialsoc.org.uk/publications/the-bss-bulletin/ > <http://www.sundialsoc.org.uk/bulletin.php> > > > > -- > *From:* "Keith E. Brandt, WD9GET" > *To:* sundial > *Sent:* Friday, 11 August 2017, 21:09 > *Subject:* Barrington Court multi-face dial > > Could someone point to/send me a description of the multi-face dial at > Barrington Court in Somerset? I'm only finding pictures via standard web > searches. > > -- > ~~ > Keith E. Brandt, MD, MPH > *wd9...@amsat.org* > > > > *Christianity and science are opposed… but only in the same sense as my > thumband forefinger are opposed- and between them I can grasp everything.* > —Sir William Bragg (Nobel Prize for Physics- 1915) > > *This message transmitted with 100% recycled electrons > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > -- > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Fwd: Spackman, Green, and Cole
Don't know if I sent this ti the list, or just to Wolfgang. Apologies if it's a duplicate. Some of the papers of Arthur Robert Green are in the University of Southampton. He was involved in an amateur local historical society in Hampshire, England, and is described as "Dr". While this title may of course be a PhD, it's worth checking if he was simply a medical doctor. See: http://www.southampton.ac.uk/archives/cataloguedatabases/ webguidemss75.page Best wishes, Patrick *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 6 April 2017 at 05:08, Wolfgang R. Dick wrote: > Dear Karlheinz, > > > T. W. Cole, who wrote Origin and use of Church Scratch Dials, London > 1935, > > which is only one of his publications. > > There are more publications by him. From different sources I compiled: > > Cole, T. W. The Origin and use of Scratch-Dials (London, 1935), > reprinted 2001 > > Cole, T. W. Classification of church scratch-dials. 1935 > > COLE, T. W. Scratch-dials and medieval sun-dials. > History and relation to scientific sundials. (Stratford St. Andrew, 1938 > > Cole, T. W. Scratch dials or medieval sundials : > supplementary list to the list given in "Origin and use of church > scratch-dials". > Stratford St. Andrew, Saxmundham : [Privately published 1945] > > Cole, T. W. Church Sundials in Medieval England: > Reginald Taylor Prize Essay 1945. 1947 > (Also cited as: Cole, T. W. Church sundials in medieval England. > Brit. Archaeol. Assoc. Jour. for 1945-7, 3rd ser. X (1948) 77-80. > [Reginald Taylor Prize Essay, 1945. Summarised by A. J. Hatley.]) > > Perhaps this publication in Brit. Archaeol. Assoc. Jour. contains > some biographical information, because it is related to a prize. > > > Two more findings: > > David A. King, George Saliba: From deferent to equant: a volume of studies > in the history of science in the ancient and medieval Near East in honor > of E.S. Kennedy. 1987, p. 138: > "These wall dials, often called scratch dials, are described in Zinner, > 1964, and in a series of three pamphlets published privately by T W. Cole > ..." > > Norfolk Archaeology, Or, Miscellaneous Tracts Relating to the Antiquities > of the County of Norfolk, Vol. 25, 1935, p. 452: > "Mr. T. W. Cole, of London, is making an effort to record and classify > the primitive sundials, or scratch dials, on churches: hitherto the > recognition of the subject seems to have been general rather than exact. > Mr. Cole has published an interim list, ..." > > I could not find his first name(s). > > Best regards, > Wolfgang > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Dial face colouration
When taking light meter readings for photography, it is common to use an 18% grey card in place of the object which will actually be photographed. This is generally considered to give a reading which will accurately balance light and dark. See: https://en.wikipedia.org/wiki/Gray_card Might be worth examining as an ideal tone for a sundial? *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 26 February 2017 at 12:08, John Lynes wrote: > There is no single optimum reflectance for a flat dial face. Obviously > under dim sunlight the optimum reflectance would be 100 per cent, > i.e.perfect white. > Under intense sunlight, contrast sensitivity would be optimised for a > lower value of reflectance. Thousands of papers have been written on > contrast sensitivity. One classical study is "Brightness and contrast in > illuminating engineering" by RG Hopkinson, WR Stevens and JM Waldram, > Transactions of the Illuminating Engineering Society (London), Vol 6, No 3, > pp 37-48 (1941). This indicates that when the sky illuminance on a matt > dial face is over about 50 lumens per square foot (about 500 lux) the > optimum reflectance would be about 60 per cent (a light grey, about Munsell > Value 8). Below this illuminance (which would correspond to a solar > altitude close to sunrise or sunset) the optimum reflectance would rise > quite sharply. > Note however that the maximum sky illuminance considered by the authors > was 1000 lumens per square foot (corresponding to a solar altitude of about > 20 degrees). Higher illuminances might further reduce the optimum > reflectance. > John Lynes > > On 26 February 2017 at 02:25, Michael Ossipoff > wrote: > >> It seems to me that Steve's question has been mostly disregarded rather >> than answered. >> >> Not having experience with translucent dial-faces, I didn't know about >> their lack of accuracy, and I certainly can't disagree with what two people >> have said about that. >> >> It means that the advantage of a translucent dial, for omnidirectional >> reading, comes with a disadvantage of less precise accuracy. >> >> But of course a high-mounted dial intended for relatively distant reading >> might not be as concerned with fine accuracy as with omnidirectional >> viewing. And so translucent dials for all-directions viewing certainly >> aren't ruled-out. >> >> Steve's main question was about the choice of dial-face hue, saturation >> and brilliance, for easy and safe dial-reading. It seems to me that Steve's >> question has been mostly disregarded and discounted rather than answered. >> >> I lied. >> >> I said that I can't speak from experience on that matter. >> >> But my experience with a few paper-on-cardboard tablet-dials is >> sufficient to say this: >> >> From my experience, I can say that you definitely don't want a white >> dial-face. >> >> As I said, my first dial had a white dial-face. After that, I switched to >> brown, which was a big improvement in usability. >> >> I suggest brown instead of white. >> >> Someone implied that, the more contrast (between light and shadow), the >> better. Not so, when the dial-face is too white to look at in bright >> sunlight. >> >> As for gray: Gray reflects the visible wavelengths in a relatively equal >> mix, resulting in no perceived hue. If some hues are (at least relatively) >> to be avoided, then obviously gray isn't what you want. >> >> At each end of the visible spectrum, there is, of course, radiation that >> isn't visible. >> Infrared (IR) and ultraviolet (UV). >> >> One possible disadvantage of that is that, when you don't perceive it or >> its intensity, then of course you could conceivably get a dangerous amount >> (accutely or cumulatively) without any perception of it. >> >> For example, never look at the sun when, due to a haze, or due to the sun >> being low in the sky, the sun doesn't look bright. You don't have any >> perception of how ingtense the UV or IR is. It could burn your eye without >> any feeling of discomfort. (I don't know which of those is more dangerous, >> but there have been official warnings to never look at the sun when it >> seems less bright due to haze or low altitude.) >> >> Aside from that, there's been evidence that, when people spend a lot of >> time outdoors, in bright sunny climate, then many years of exposure to the >> bright blue light can cause some long-term cumulative damage. So maybe blue >> isn't the most desirable hue. &g
Re: Genuine or not?
Compass doesn't look quite right - if it's German I might expect East to be written as Ost. *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 20 February 2017 at 12:22, Michael Ossipoff wrote: > It doesn't seem genuine to me. > > It isn't just that there doesn't seem to be a way of moving the upper end > of the string to the other latitude-marks. It's also that you can't just > change the angle of the gnomon, for a different latitude, and use the same > hour-lines. > > So there seems to be no purpose for the latitude-marks on the inside of > the vertical, piece--other than to make it look adjustable for latitude. > > Michael Ossipoff > > On Mon, Feb 20, 2017 at 9:57 AM, Dan-George Uza > wrote: > >> Hello! >> >> There's a diptych sundial on sale for about 80 euros supposedly dating >> from 1920. >> >> Do you think this is genuine? I think it is a modern replica. >> >> http://anticariatulnou.ro/diverse/antichitati-artizanat-cole >> ctionabile/cadran-solar-cu-busola-antica-din-lemn-diptic.html >> >> The string does not seem to be adjustable for latitude, I see only one >> hole (it's fixed at 42 deg.). Why then go through the trouble of printing >> the latitudes for European cities on the back? >> >> One thing I find interesting is the plumb bob and the orifice on the >> vertical plate. I think it is meant to align the piece to the vertical. I >> haven't seen this before. >> >> Thanks, >> >> Dan Uza >> Romania >> >> --- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >> > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Astrolabes
First post here, so I don't know if I'm doing it right! Here are a couple of links to reproduction astrolabes, but I have no idea as to their precision: http://www.puzzlering.net/astrolabe.html http://www.astrolabeshop.com/us/astrolabes-page1.htm Some people with considerably more skill than me have made their own, and the level of accuracy looks very superior. That said, some have taken hundreds of hours of work! Have a look at the site of the late James E. Morrison for some fascinating examples: http://www.astrolabes.org/pages/individual.htm Best wishes and season's greetings to all! Patrick *Patrick Vyvyan* *Presidente* *Corporación Cultural de Putaendo* On 22 December 2016 at 09:24, Dan-George Uza wrote: > Dear group, > > While visiting the Barcelona CosmoCaixa this spring I saw a wonderful > looking astrolabe on display in the science museum gift shop. > > It is the one listed below: > > http://www.antiquus.es/p-172/Orientacion-y-Medida/Astrolabio/Astrolabio- > Arsenius-20-(dos-latitudes) > > This brass plated astrolabe measures 20 cm / almost 8" and it comes with > two base plates for two different latitudes (41 and 45 degrees). > > I was very tempted to buy it but after doing some research back home I > found that there are some inaccuracies in the rete and alidade design. They > are pointed out in the link below (in Spanish). > > http://www.oagarraf.net/Comunicacions/ASTROLABI/INDEX%20ASTROLABI.html > > Can you sugest other working astrolabes in this price range? > > > Dan Uza > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
