Gregor Reisch's Margarita philosophica, an encyclopedia intended for younger students, first appeared in Freiburg, Germany in 1503, the same year Reisch became the prior of the town's charterhouse. Divided into twelve chapters, all filled with charts, diagrams, and block prints, the work remained a popular text for many years. The section on astrology has a fine example of the "zodiac man." Each sign of the zodiac corresponds to a different part of the body. Zodiac men were very popular images which depicted the relationship between parts of the body and their celestial governors. The diagrams also served as reminders of how the microcosmos reflect the macrocosmos and the connection between earthly and celestial affairs. Zodiac men images were widely copied and reproduced and are still found today in almanacs. The second image depicts the astronomer Ptolemy or Claudius Ptolemaeus (second century AD), author of the Almagest, one of the most important treatises of mathematical astronomy of antiquity. Ptolemy holds to his eye a quadrant, an instrument for measuring in degrees the altitude of a celestial body (used for time reckoning). His crown is an unusual adornment because he was not a king or prince. Urania, the muse of astronomy, stands behind him, pointing to the heavens and directing his gaze. Near Ptolemy's feet, on the ground, is a discarded armillary sphere (for a description of this instrument, see: Sphaera mundi, 1490.) The third image on this page depicts Urania displaying the cosmos as visualized during the 16th century. The man in the center, Atlas, obscures the earth at the center of the concentric rings in a geocentric or earth-centered cosmos. Moving outward, each ring corresponds to a planet, beginning with the moon and ending with Saturn, the most distant planet visible to the naked eye (the next planet, Uranus, was not discovered until the 18th century). The ring after Saturn is the Firmament, the realm of the fixed stars (stars were not found to be in motion until the 18th century). Beyond the fixed stars are circles which represent the mechanism by which the planets appear to move, the crystalline spheres and the Prime Mover, and beyond is the realm of God and the angels. Atlas, the Titan in Greek mythology who is frequently depicted holding the earth on his shoulders, stands at the middle with a sheepish expression.