At 08:20 PM 11/17/99 +0000, Frank Evans wrote: > >It looks to me to resemble the arrival of the earth-aligned gnomon in >sundials. We understand that the axial gnomon was introduced from the >Arabs, but when? On what evidence? Modern sundials seem just to have >appeared around the fifteenth century. Yes, maybe the Arabs had them >before but there is such a thing as reinventing the wheel. And the >incentive would be the invention of the mechanical clock with its equal >hours. We have medieval dials and medieval clocks in my latitude where >day length varies from 8 hours to 16 hours and thus unequal hours differ >hugely from equal hours. Can anyone throw some light on this? Is there >written evidence of the arrival of the axial gnomon into Europe? > Hi Frank,
Good question. 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. Can anyone confirm the existence of such a dial? 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. Who introduced the concept to Europe? Where are the oldest examples? Your challenge remains unanswered. The oldest dial that I've actually seen is the one in your part of the world, the vertical dial showing prayer times on the old church in Kirkminster, North York. Thanks for fixing the date ~1063 and location for me and providing the translation of the inscription. Roger Bailey N 51 W 115 * the actual quotation is: "1200 - MAROC : Abdul Hassan Ali ecrit un gros traite consacre en partie aux cadrans solaires. Il y parle du style incline selon l'axe du monde (style polaire).
