right a ray of sunlight penetrates the roof of a dark cave, and a mirror casts reflections on the wall of the cave. This is a representation of Plato's famous allegory of the cave. Universal horoscope of the Society of JesusArs Magna Lucis et Umbrae'' contained many designs for sundials and related devices, including a large foldout sheet that allowed the user to know the time in every part of the world where the Jesuits had missions. Kircher intended to be of practical use, and suggested that it be mounted on wood, and then oriented precisely by use of a sundial. The rose at the bottom of the sheet could be cut out and mounted on stiff paper so that it could be rotated to show the hours. The main design is in the shape of an olive tree. When the sheet is hung vertically, with pins placed at the nodes of the tree, the shadows of all the pins align to spell "IHS", the logo of the Society of Jesus. Magic lantern Kircher's unusual depiction of the magic lantern has been taken by some critics to mean that he had not actually built one or seen it operate, since the illustration shows the mirror not properly alighted with the light source and the glass slider appears in front of the lens tube rather than behind it. Some argue that these anomalies are due to mistakes by the Dutch publisher Waesberghe; however others hold that the mechanism would work as depicted and that it was a variant of the normal type, designed as an analogicical demonstration of the Neoplatonic metaphysics of light. External links digital copy of Ars Magna References Light 1646 in science 1646 in Italy Optical phenomena Shadows Athanasius Kircher