A few weeks later, on December 24, 1824, Roget lectured on the persistence of vision with regard to moving objects, a phenomenon first recognized by the ancient scientists. Plateau wrote in 1828 as follows: I have made an instrument by means of which I could produce these fixed images with ease and I also could make visible the formation of changes in the curvature ... when working at my first experiments relative to sensations, I observed that while turning rapidly a wheel whose teeth were perpendicular to its axis, and placing the eye at some distance from the plane of the axis, one perceived the image of a series of perfectly immobile teeth; that also with two wheels revolving, the one behind the other, with considerable speed and in opposite directions, produced in the eye the sensation of a fixed wheel. I have remarked further that, while the two wheels are not concentric, the fixed image appears to be made up of curved lines. Today stroboscopic machines, based on the principles of Plateau’s devices, are used to study moving objects. In this way modern scientists learn more about the nature of movement and its stresses on wheels and other objects. Plateau received the degree of doctor of physical and mathematical sciences from the University of Liége on June 3, 1829, when he was 28. His thesis was on “Certain Properties of the Impressions Produced by Light upon the Organ of Sight.” It is strange that such a learned paper would have so much influence on what was to be the modern motion picture. The chief points--all of importance in building motion pictures--of the Plateau thesis dated April 24, 1829, were: First, the sensation (result of the picture presented to the eye) must stay for a time to form completely--this hinted definitely at the necessity of intermittent movement for a really successful and practical motion picture machine. Second, the sensations do not disappear immediately but gradually dim--this makes motion pictures possible. If each image disappeared all at once, only individual still pictures would be recognized. The gradually dimming makes possible fusion of one image with the next which results in appearance of motion. The third point covered was the relative effect on the eye of various colors. Plateau concluded that the intensity of the chief colors decreased from white, yellow, red, blue--in that order. He also announced results of perception of various colors at different angles, studies made in the shade and in the light. It was further pointed out that two colors--as two images--changed rapidly result in only one sensation or image. After receiving his doctor’s degree from the University, Plateau taught at the Royal College of Liége while he continued his research on vision and related matters. [Illustration: Annuaire, L’Académie de Belgique, 1885 _JOSEPH PLATEAU sacrificed his own eyesight in an effort to enable others to see pictures in motion._]