...ht thus resemble the analemma, described by Vitruvius, which, by marking the length of the shadows of a fixed gnomon, showed the different altitudes of the sun at the different seasons of the year. Grotius supposed the dial of Ahaz to be a concave hemisphere with a central globe whose shadow fell on the lines engraved on the concavity. This would resemble the Greek scapha, a semicircular concave di...