Abstract

The designer of the Prosymna globe included a north-facing network of lines which also utilizes the sunlight-shadow boundary as it passes through the hour holes used with the south face. Again intersection between appropriately marked boundary and day curve marked the hour. The resulting network is appropriately similar to the network on a roofed spherical dial, for the shadow boundaries which determine the one are orthogonal to the rays of sunlight which cast an image of the sun on the other. A third network of lines stretches between the east and west hour holes across a shallow hole in the globe´s meridian. I interpret it as a secondary south-facing map of the moving boundary between sunlight and shadow. The three great semicircles which form part of the network are divided by points which would lie along the hourly positions of the boundary at winter solstice (lower semicircle), equinox (middle semicircle), and summer solstice (upper semicircle). Three separate networks of lines have been engraved on this spherical stone. Two great circles on the sphere correspond to the meridian and horizon circles. A conical hole with base 100 mm in diameter pierces the globe at the lower pole.