Hello Colleagues, The Piedmontese painter and sundial maker, Giovanni Francesco Zarbula left an amazing legacy in the villages of the French alps. Between 1832 and 1870 he crafted over 60 sundials in the area from Grenoble to Gap, near the Italian border. Over half of these flamboyant folk art masterpieces still survive; recently many have been expertly restored. I often wondered how Zarbula laid out these designs on vertical declining walls. As an itinerant craftsman, carrying all the tools of his trade on the back of a mule, he would not be able to utilize the methods summarized in Frank King's note following John Carmichael's good question. How did he do it?
I am pleased to report that Google found the answer for me. Follow the link to: http://www.meridianeitaliane.it/Rivista%20Gnomonica/gnomonica6.pdf On pages 8- 10 of this 61 page edition of "Gnomonica", there is a letter by Alessandro Gunella outlining Zarbula's method: "L'orolgio Francese e il metodo DI ZARBULA per trovare la declinazione del muro". Thanks, Alessandro for answering the question. I guess that I am not the first to be impressed by Zarbula's dials and wonder about his techniques. As Alessandro reported, Zarbula didn't actually measure the declination of the wall. He didn't need to. Zarbula seems to have applied a variation of the "Indian Circle" technique (Cassini's Method on Frank King's list) to establish the equinoctial and sub-style line on the wall. From these he could lay out the hour lines using well known graphical gnomonic techniques. The "Indian Circle" method ("cerchio indu" in Italian) is a simple technique for finding north. All you need is a stick, a string and sunshine. Put the stick vertically into the flat level ground. Use the string to describe some circular arcs, using the stick as the center. Watch the shadow of the tip of the stick and note where the path of the shadow tip crosses the arc in the morning and then again in the afternoon on the other side of the circle. The line between the crossing points is due east - west. North - south is perpendicular to the east - west line. Zarbula's method is based on the fact that every vertical declining sundial has an analogous horizontal sundial somewhere else in the world. To apply this variation to a declining wall, all you have to do is mount a stick perpendicular to the wall, draw one or more concentric arcs, mark the shadow tip crossings on the wall, and draw a straight line through them. This line is the equinoctial line, (equinoziale in Italian), the intersection of the equatorial plane with the plane of the vertical declining wall. This important construction line is highlighted in most of Zarbula's dials. A perpendicular line from the equinoctial is the sub-style line (sostilare in Italian) for the polar axis parallel. QED I hope that I got this right as I used Babblefish to transliterate Alessandro's note and some points may have been lost in translation. The web link brings up the whole pdf file, 3.6 MB. If any one wants to have a copy of the extracted pages, a 60 kb file and/or my interpreted translation based on Babblefish, I would be pleased to send them on as email attachments. I assume Alessandro Gunella or Nicola Severino of Gnomonica will allow such single copies to colleagues within the copyright laws. I am continuing my research on Zarbula, his methods and his dials. If any one has information to share on these topics that doesn't come up among the ~200 Google hits on "Zarbula", I would appreciate a note. Regards, Roger Bailey Walking Shadow Designs Now back at N 48.6 W 123.4 -
