Johannes Kepler, the great astronomer, advanced the art-science of magic shadows by developing the theory of the projection of images as well as the scientific use of multiple lenses and the _camera obscura_ or “dark chamber”. Da Vinci told how the camera could be used; Porta tried it out for entertainment on a considerable scale but there still was need for penetrating attention from a scientist. That Kepler supplied. Kepler was a precocious child though he suffered from poor health. He had no special interest or inclination towards astronomy until in 1594, at the age of 23, he found himself required to teach a class in that subject. Soon he became an expert and before his death announced the Kepler laws explaining the planetary system. In 1600 Kepler became assistant to Tycho Brahe (1546–1601), the greatest practical astronomer to that date but one who rejected the Copernican theory that the earth and planets revolve around the sun, a theory which was firmly proved by Kepler. Brahe lost the tip of his nose in a duel, so he wore a gold one, carrying with him cement with which to stick on the tip whenever it fell off. A few years after becoming astronomer to the Emperor, Kepler published, in 1604, _Ad Vitellionem Paralipomena_--“Supplement to Witelo”; Witelo, a Pole called Thuringopolonus, wrote a treatise on optics about 1270. He was a contemporary of Roger Bacon. Kepler used da Vinci’s parallel of the eye and the room camera and set the latter’s principles on a firm scientific basis. Kepler wrote, “This art, according to my knowledge, was first handed down by Giovanni Battista Porta and was one of the chief parts of his _Natural Magic_.” (But, as the reader recalls, Porta was not the first to know about the _camera obscura_ and was not its inventor but only a popularizer.) “But content with a practical experience,” Kepler continued, “Porta did not add a scientific demonstration. Yet only by the use of this device can astronomers study the image of the solar eclipse.” Kepler then described the _camera obscura_ or “dark chamber,” adding an interesting observation. He proposed that the spectator should keep out of the daylight for fifteen minutes or a half hour before he planned to use the camera so that he could get his eyes accustomed to the darkness in order to observe the images more clearly. Kepler then instructed that the objects to be represented should be placed in bright light, either of the sun or lamps. He also noted that the objects were reversed, and remarked that the images appeared in the colors of the objects. Kepler also explained that a diaphragm was needed to control the amount of light admitted to the camera, and that best results were obtained when the sun was near the horizon.