Roger Bailey wrote: > [...] When was the axial gnomon invented? The hemispherium was > used by the Babylonians and the armillary sphere by the Alexandrian Greeks. > It is a small step from these instruments to the equatorial dial with an > axial gnomon, but who first used the axial gnomon with the hour angle reduced > to the plane? I have two vague references. In "Mathematics for the Million", > Lancelot Hogben credits the Moslems, depicts a "Moorish" sundial and > obliquely refers to a dial at the great Moorish university that flourished in > the tenth century in Seville. > [...] > A slightly better reference is in the wonderful picture book by Pierre > Putelat "Cadrans Solares des Alpes". In the 'petit historique' he notes that > "Abdul Hassan Ali in Morocco about 1200 wrote a great thesis dedicated in > part to sun dials. He speaks of the style inclined in accordance with the > axis of the earth." Earlier references to Moslem dials usually show a > vertical gnomon and mark prayer times when the shadow lengths are one and two > times the gnomon height. > [...]
Dear all, The above-quoted treatise by Abu Ali al-Hasan ibn Ali ibn Umar al-Marrakusi (fl. first half 13th century) was partly published in a French translation in: Jean-Jacques Sédillot & Louis-Amélie Sédillot, Traité des instruments astronomiques des Arabes composé au treizième siècle par Aboul Hhassan Ali, de Maroc, 2 vols. (L'Imprimerie Royale, Paris, 1834/35) [reprinted in 1984 by Fuat Sezgin, Veröffentlichungen des Institutes für Geschichte der Arabisch- Islamischen Wissenschaften an der Johann Wolfgang Goethe- Universität (Frankfurt am Main)]. The whole second volume of this work is devoted to tracing hour lines on plane, cylindrical, concave and convex surfaces with gnomons in any conceivable orientation. ================================================================ * Robert H. van Gent * Tel/Fax: 00-31-30-2720269 * * Zaagmolenkade 50 * E-mail: [EMAIL PROTECTED] * * 3515 AE Utrecht * Home page (under construction): * * The Netherlands * http://www.fys.ruu.nl/~vgent/ * ================================================================
