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Giovanni Francesco Zarbula was a mural painter and sundial designer from Piedmont Italy who created a hundred or more vertical and vertical declining sundials in the French and Italian Alpes between 1830 and 1881.He worked exclusively in Savoy, in Piémont, the Valley of the Ubaye, le Queyras and around Briançon. 〔 ==Laying out the dial== Zarbula's method was one of observation then geometric construction. He did not need to know the latitude or declination of the wall, he did not use tables or calculations he just worked directly on the wall. All his dial were within 2° of the 45th parallel, simplifying the construction, and all gave five-minute accuracy. *With a plumb bob he drew a vertical line on the wall. This is the Noon Line. *He hammered a rod into the wall at right angles to the vertical. This is known as the centre of the dial, C *He observed and marked the shadow thrown by the tip of that rod, throughout a day. This line, technically known as a hyperbolic declination line. *Using a set of compasses, he determines the line of symmetry on the wall. This is the substyle line. All the rest of the dial was laid out using a 45° square, with a 15° measure at the end. * He drew a horizontal line at a point of choice on the dial plate. This was the Horizon. * The square was placed on the substyle facing outwards, it is slid into any convenient position where it cuts the horizon, and he drew a perpendicular line drawn to that point. This line is called the equatorial. A line was drawn from that point to the centre of the dial; it was the 18h line (or 6h depending on the declination (d) of the wall). The points where the equatorial crosses the noon line and where the equatorial crosses the substyle line were important. * He placed apex of the square on the substyle line, so the sides passed through the equatorial points mentioned. (The 12h and 18h markers). The apex point is called the auxiliary equatorial centre. * A protractor or squares drew off 15° intervals on the equatorial. These were connected to the centre of the dial: the hour lines. The distance from the auxiliary equatorial centre to the equatorial formed the substyle height at that point.〔http://www.ens-lyon.fr/RELIE/Cadrans/Promenades/Zarbula/Equerre〕〔 File:Zarbula-Hindu Circle.png File:Zarbula-set-hourlines.png File:Zarbula-auxiliary-equatorial-centre.png File:Zarbula-set-hrs-on-equatorial.png File:Zarbula-dial-face.png 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Giovanni Francesco Zarbula」の詳細全文を読む スポンサード リンク
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