Dear friends, a new issue of the Italian magazine Orologi Solari is available for download from the usual site http://www.orologisolari.eu/.
Here is the list of articles together with a short abstract: 1. - "The Erfurt Rule" by Paolo Albéri Auber The "Erfurt Rule" is described by the German researcher Karlheinz Schaldach in a "Mitteilungen" article in 2021. The comparison of the angular data of the Rule with the angles obtained through different elaboration allows us to conclude that, in all probability, the Rule was compiled in an elementary/practical way by showing on a south-facing vertical wall the equinoctial temporal values recorded on a Roman horizontal clock, of which at least one is preserved in the Museum of Wiesbaden. It is clear finally that the Braunschweig Cathedral sundial is an "astronomical hours" sundial and not an "ancient/ temporary hours" one. 2. - "The name of hours. For a more correct gnomonic lexicon - third part" by Mario Arnaldi In this third and last part of the article the author reflects on the name of equal hours. Even these had no precise name in ancient time if not that of Equinoxial, or Natural in the late Middle Ages. The distinctions with a specific name came up later, between the fifteenth and sixteenth centuries. Have the names we use today a historical and philological basis or they are the result of improper habits? 3. - "The calculation of solstice date with Eustachio Manfredi’s method" by Giuseppe De Donà The author reproduces the experience of Eustachio Manfredi, described in the "DE GNOMONE MERIDIANO BONONIENSI" to calculate the date of the solstice, using a small ‘camera obscura’ sundial, the Spica star and a clock. 4. - "Can we make a sundial on the Moon?" by Luigi Massimo Ghia A study is performed using the software "Stellarium" in order to demonstrate what a horizontal sundial can look like on the Moon. Stellarium allows us to position ourselves on any celestial body and from there to derive the position, orbital and visibility parameters of any other celestial body. 5. - "A hat for the sun (A visual tour of Europe hatsundials)" by Manuel Pizarro The author presents a very unusual and practically unknown type of sundial. Through his extensive research in literature, we know that the brim or hatsundial has its origins dating back to the thirteenth century and that contemporary avant-garde designers have used it in uncommon places such as a revolving restaurant or a hydroelectric dam. 6. - "Italian or French hours?" by Elsa Stocco In the controversial and chaotic transition from the Italian to the French hours system, in the late eighteenth-century Venice, erudite dissertations of more or less known authors, highlight the disadvantages that arise from the use of italian time and provide tools to easily switch from the old to the new time system. 7. - "Calibrate a pseudo-sundial (Short Contribution)" by Francesco Caviglia Some sundials have gnomon and hour lines that are not coherent with the right gnomonic principles. In this case, with an appropriate "calibration" (a table indicating the right time according to the time indicated, if necessary tabulated for the different days of the year) it is possible to use them to know the time, or at least to understand how much they are wrong. An Excel spreadsheet is offered to the purpose. 8. - "Gnomonics by Guarini (Short Contribution)" by Alessandro Gunella The author offers us the translation of the second book of the “Caelestis Mathematicae - Geometricas Umbrarum” by Guarino Guarini (1624 - 1683) where Guarini deals gnomonics with very original graphic methods, referring expressly to the general principles of Geometry, and treating rather fussy the whole matter. Hope you will enjoy the reading, although in Italian only. Ciao ! Gian
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