De Chales’ monumental work is _Cursus seu Mundus Mathematicus_, “The Mathematical World,” written in 1674. An edition, edited from the author’s reviewed manuscript, by Amati Varcin, S. J., was published at Lyons in 1690, 12 years after de Chales’ death. One section was devoted to optics. De Chales studied the eye and knew that the image is upside down on the retina. He investigated other vision problems, including angular vision and vision at long range, considered binocular vision and the images formed by each eye. He devised satisfactory lenses and spectacles for both far and near-sighted persons. (The original name for near-sightedness--“Myopia”--came down from Aristotle.) De Chales experimented with light and dark colored objects and gave consideration to why we see better with two eyes than one. He noted that the eye actually sees color and light and not objects and movement--a fact upon which the whole motion picture process is based. He pointed out that the ship appears to stand still and the shore moves to an observer aboard. He also studied the nature of color and the laws of light. De Chales even attempted three dimension projection! Even now many efforts are being made to achieve “three dimension” motion pictures without the use of special glasses or other viewing devices for the spectators. [Illustration: Oculus Artificialis Teledioptricus, 1685 _Time and wind indicators by projection were among the curious adaptations of the magic lantern device developed by Zahn. Above, the hour was indicated by the point of the sword. Below, the wind instrument was ingeniously connected to a vane on the roof. It was automatic in action; the “clock” was not._] De Chales considered plane and curved mirrors, improving the design of the old _camera lucida_ of Alberti by introducing a mirror. He devised a simple searchlight to improve the projection of images, in a system similar to Kircher’s design for the first magic lantern, but as it had a stronger light source it was shown how letters, bright enough to read, could be projected a great distance. De Chales narrated how fires could be set with the two lens system--as the old Burning Glasses of Archimedes. He was a practical man as well as an ingenious one and included details on how to make lenses. Other studies included consideration of color reflection, a telescope with two convex lenses, an attempt to make binoculars and even an experiment with prisms, laying some of the groundwork for Newton.