--- Begin Message ---Dear Roger and All, I'm not really sure that the Romans (or the Greeks and Romans) did not use even gnomons inclined. The Archaeological Superintendence of Pompeii I was assured that the sundial that I enclose in the original photo has the original gnomon inclined. I put an excerpt from my book De Monumentis Gnomonicis apud Graecos et Romanos, published in 2005 and a link to see the full PDF. Here you can see that also Sharon Gibbs wrote (1980, Greek and Roman Sundials) about this: Gibbs (p. 79) alludes to this fact considering that comparisons of the relative positions of the shadow Sixth Time(noon) on any horizontal clock shows that the gnomon was not placed vertically in the holeIt preserved to accommodate him, but was inclined towards the North Pole (examples 4001G, 4002G, 4004G, 4005G).Greeting to all, and the best wishesNicola Severino Link PDF of my bookhttp://www.nicolaseverino.it/LIBRI%20MIEI%20EDIZIONI%20ILMIOLIBRO/De%20Monumentis%20Gnomonicis%20libro%20completo.pdfUno gnomone unicoSiccome lo gnomone di questa meridiana, che ha dell'incredibile anche per la sua unica forma di piccolo obelisco, èinclinato come un assostilo, è facile pensare che sia solo il risultato di un maldestro restauro. Ma la base dellognomone che vedremo nel prossimo orologio orizzontale, e che è assolutamente originale, fa pensare che anche inquel caso lo gnomone fosse si tipo inclinato e parallelo all'asse terrestre. Che i Romani utilizzavano lo gnomonepolare per gli orologi orizzontali? Nessuno degli esemplari descritti da Gibbs possono aiutarci in questa possibileinterpretazione. Nessuno di essi conserva uno gnomone originale, come invece in questo caso di Pompei dove lamaggior parte dei reperti si sono conservati in modo perfetto. Gli gnomoni originali di questi orologi orizzontali,relativamente, piccoli, costituiscono una scoperta eccezionale nella gnomonica, ma il fatto che essi potessero esseredel tipo parallelo all'asse terrestre va contro ogni possibile teoria matematico-astronomica adattabile all'epoca.Eppure la forma triangolare del foro che ospita lo gnomone, come quello dell'altro orologio orizzontale che andiamoa descrivere tra poco, fa pensare che esso fosse proprio inclinato e non ortogonale. Ora devo aggiungere che Gibbs(pag. 79) accenna a questo fatto considerando che le comparazioni delle relative posizioni dell'ombra dell'ora Sesta(mezzogiorno) su qualche orologio orizzontale mostra che lo gnomone non fu piazzato verticalmente nel bucopreservato ad ospitarlo, ma fu inclinato verso il polo Nord (esempi 4001G, 4002G, 4004G, 4005G). Lagiustificazione di questo fatto è la stessa che abbiamo dato prima, e cioè che sugli orologi greco-romani la posizionedel "piede dello gnomone" non era importante perchè solo l'ombra della punta dello gnomone indicava l'ora".Un'altro passo del libro ci fa capire che Gibbs non ha mai trovato un esemplare che conservi uno gnomone originale:Tracce di gnomoni di bronzo o ferro rimangono a coprire la testa dei buchi in cui erano impiantati.Le curve di declinazioneAltro fatto eccezionale è la presenza di sole 5 curve di declinazione solare: perchè?Gibbs riporta le immagini di soli due orologi solari che hanno un'anomalo tracciato delle curve di declinazione, manon sono orizzontali. Si tratta del n° di catalogo Gibbs 1004, ovvero una meridiana sferica con 6 curve dideclinazione e la n° 3048, quindi una meridiana conica, con sole 4 curve di declinazione. Non è facile dare unarisposta, soprattutto corretta, e le interpretazioni non possono che rimanere nel vago. Per quanto riguarda questaunica meridiana orizzontale con 5 curve diurne osserviamo che:1) Sono tracciate con buona precisione e tecnica;2) Sono state omesse le curve diurne invernali relative ai mesi di Gennaio e Febbraio;3) Un confronto con il progetto di una meridiana con ortostilo di 5 cm calcolata con un moderno PC, offre untracciato delle 5 curve di declinazione pressoché identico a quello di questa meridiana.Da quanto detto, possiamo fare le seguenti ipotesi generalizzate, di cui alcune un po' forzate e fantasiose:1) In alcuni casi, sporadici, il costruttore disegnava solo le curve di declinazione piu' importanti, cosi' come in molticasi si sono descritte solo quelle degli Equinozi e Solstizi;2) Che nel periodo compreso tra il II-I secolo a.C. e fino all'avvento del calendario Giuliano, qualche costruttore dimeridiane si atteneva ancora al vecchio calendario solare romano ereditato da Romolo dalla fondazione di Roma cheprevedeva l'anno civile in 304 giorni divisi in 10 mesi. Questa potrebbe essere l'unica ipotesi plausibile e reale,16 ----Messaggio originale---- Da: [email protected] Data: 30/07/2015 6.26 A: "Michael Ossipoff"<[email protected]>, "sundial list"<[email protected]> Ogg: Re: Temporal Hours Hi Michael and all, I don't know the dominance of temporal hours or equal hours before mechanical or water clocks were in common usage. It is clear they co-existed. It is a significant research endeavor to determine the dominance and the reasons. Meeting for lunch was no problem. Dinner was more chancy; remember the verse of Cattulis, "Cenabis bene, mi Fabulle". Once the time and location were set, the important question remained "Who is bringing the duck". Greek and Roman dials were not horizontal or vertical flat planar dials, but hemispheres, scafes or other projections of the sky onto a spherical or conical surface. Planar dials came with the Islamic dials. The first planar dial with a polar gnomon was by Ibn al-Shatir in Damascus in 1371. This dial had temporal hours, equal hours based on noon, sunrise and sunset, and Islamic prayer times, including reference lines to prayer times when the sun was well below the horizon. For me this dial is the epitome of sundials. It includes all the time systems in vogue at that time and for hundreds of years before and after. They all existed and were in common usage suited for different purposes. The question remains "Who is bringing the duck" for dinner. Time is important. Don't overcook it. Regards, Roger Bailey Michael Ossipoff Sent: Wednesday, July 29, 2015 11:57 AM To: Roger Bailey ; sundial list Subject: Re: Temporal Hours Roger, thanks for the answer. Ok, I shouldn't say that as a fact without having more information than I do. This is what I was implying or saying, without really having much support for it: "In Europe and the fertile-crescent region, in ancient, classical and medieval times, before mechanical clocks (starting with Folliet-balance clocks) came into wide use, Equal Hours were of interest, for the most part, only to astronomers and astrologers. For ordinary civil timekeeping, for arranging meetings, keeping schedules or other civil/social purposes, Temporary Hours were preferred by pretty much everyone." Were a fair percentage of people making their appointments and schedules by Equal Hours in the times and places named in the above paragraph? I'm not being argumentative--I really don't know. ---------------------------------- Thanks for reminding me about Temporary Hours lines on Flat Dials being satisfactorily approximated by straight lines. I'd temporarily (no pun intended) forgotten that. It was a question that I'd asked, and received an answer to, when I first wrote to NASS. Were Flat-Dials (for Temporary or Equal Hours) in use before mechanical clocks were getting popular? What about _wide_ use? How early? ------------------------------------- Can anyone explain why the early, inaccurate inertia-controlled Folliet-Balance clocks replaced the cheaper, more easily-made water-clocks? Were those earliest, most inaccurate mechanical clocks significantly, or any, more accurate than water-clocks? Michael Ossipoff On Tue, Jul 28, 2015 at 11:58 PM, Roger Bailey <[email protected]> wrote: Hi Michael and all, Temporal or Antique hours co-existed with equal hours from way back, thousands of years. It didn't take a technological device like a clock to cause a change. A more interesting point is the portrayal of temporal hours, 12 unequal hours in the day on a flat sundial. It is easy on Greek/Roman hemispheres but what about flat planar sundials. Is it sufficient to calculate the points for the solstices and draw a straight line between them? This works but is it right mathematically? To answer this question, Fred Sawyer gave an excellent presentation on Antique Hours at the NASS Conference in 2010 in Burlington. Was it really five years ago! Here is a clip of the abstract from the NASS website. "Antique Hour Lines: Fred Sawyer gave another excellent example of his reviews of the history of complex mathematical concepts for sundials. In the case of Antique Hour Lines, the question was “Are they straight lines?” For millennia they were assumed to be, but the assumption was questioned by many mathematicians. Proofs were offered by Ibrahim Ibn Sinan in the 10th century, Christopher Clavius in the 16th, Hellingweth in the 18th and many including Montucla, Delambre and Cadell in the 19th, offering proofs that the lines were in fact curved. The various proofs tended to be empirical based on plotting the results of individual calculation. Biot offered an analysis in 1841 and Davies in 1843, but the problem was not fully solved until 1914 when Hugo Michnik studied the curves for the equatorial sundial, providing a method to come up with non-parametric equations for the curve for each hour. Fred then presented the graphs of various hour lines at different latitudes and inclinations. The curves were amazingly complex looking but the specific area of interest, where a shadow would be projected was very close to the straight lines of the traditional method." This is why I belong to NASS, to read the Compendium and to go to the conferences. Here we see solutions to problems we didn't even know existed. Regards, Roger Bailey From: Michael Ossipoff Sent: Tuesday, July 28, 2015 4:47 PM To: Dan Uza Cc: sundial list Subject: Re: Precision: the measure of all things (I should clarify again that, for clarity, I like to capitalize _kinds_ of whatever sort of thing I'm talking about...such as kinds of sundials or hour-systems, though I realize that that capitalization is probably not officially correct.) Another closely-related interesting question is the matter of what _kind_ of hours are used. Of course every book or article on sundials points out that, before mechanical clocks became widespread, civil time was measured in "Temporary Hours", which divided the day, from sunrise to sunset, into 12 equal parts, and likewise divided the night, from sunset to sunrise, into 12 equal parts. Those books and articles nearly always imply or say that equal hours was a new invention when it was adopted--that someone invented a new way to designate time, and so it was adopted. Another frequent, and related, statement or implication is that the Horizontal Dial was an innovation that was came into use upon its invention because, before that, its possibility was there, but just hadn't occurred to anyone. But I read different. I read that Equal Hours were in use by astronomers and astrologers long before they were adopted for civil time, and so they were hardly a new invention at the time of their adoption for civil time. In fact, look at a Hemispherium or Hemicyclium. Designed to read in Temporary Hours, its hour-line, for a particular hour, crosses a different Equal-Hours line, according to the declination. Whether those Temporary Hours were drawn by calculation, or by empirical observation, it's plain that it would have been obvious to the dial-maker that he was making the 3 p.m. hour-line cross different Equal-Hours lines at different solar declinations. One thing that I'm objecting to is that many of those books imply that Temporary Hours are more primitive, and Equal Hours are something more advanced that therefore, when invented, immediately replaced Temporary Hours. Primitive? Rather, a lot more complicated and laborious to make. For sundials, and likewise for water-clocks. People should be impressed by the ingenuity and determination of early makers of sundials and water-clocks, who devised Temporary Hours markings and mechanisms for them. As for the Horizontal Dial, of course it's for Equal Hours. That's what it's convenient for. Sure, Flat Dials, including Horizontal Dials, and Polar Dials, and Equatorial Dials, and others, could have likewise been made for Temporary Hours, but they wouldn't have been easier to mark than a Hemicyclium. So it isn't surprising if the Horizontal Dial came into use around the same time as Equal Hours. What I read was that, though Equal Hours were well known and used by astronomers and astrologers, no one wanted them for civil timekeeping. Hence the effort and ingenuity used to devise Temporary Hours sundials and water-clocks. But, when the mechanical clock was invented, and came into relatively wide use (as tower-clocks, and in some homes), it was so much simpler to make clocks for Equal Hours, that, as a result, Equal Hours replaced Temporary Hours, for that reason of pure manufacturing-practicality. (By the way, were the early mechanical clocks, the Folliet Balance intertially-slowed clocks, without the fusee compensation, any more accurate than water-clocks, which were much cheaper and easier to build?) Temporary Hours surely made a lot of sense in agricultural societies, where it must have been very important and practical for farmers to know what percentage of the day remained. I don't advocate a return to Temporary Hours, because, speaking for myself, it seems to me that finding what percentage of the day is over, and how much or how little remains, seems a bit pessimistic, and maybe not a good way to name the time of day. ...but I realize that it had practical importance in agricultural societies. Michael Ossipoff On Mon, Jul 27, 2015 at 5:59 PM, Dan Uza <[email protected]> wrote: Hi everyone, If you haven't already, you might want to check out the first part of the documentary "Precision: the measure of all things". It's about the measurement of time and length, featuring the topic of sundials. There's an interesting theory about how the day got split into 12 hours because this number is highly divisible (but why not 60?). I just watched it on Da Vinci Learning. Dan Uza Romania --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.6081 / Virus Database: 4392/10325 - Release Date: 07/28/15 No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.6081 / Virus Database: 4392/10332 - Release Date: 07/29/15<<attachment: polare.JPG>>
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