Solar clock. Illustration showing a design for a solar clock. In the centre of the bowl is a glass sphere, this focuses sunlight onto the interior of the bowl. The light burns a track on the inside of the bowl. Above this is the interior engraving of the bowl laid out, with different tracks for different times of the year and a magnetised pointer to determine north to ensure the clock is aligned correctly. This engraving comes from the Ars magna lucis et umbrae by Athanasius Kircher, published at Rome in 1646.