Roget's palisade is an optical illusion occurring when a spoked object travels behind a picket fence or palisade. The spokes appear distorted, curving upwards or downwards depending on the direction of movement (it is easiest to see this when staring at the center of the wheel). The distortion is caused by the afterimage of the visible parts of the wheel, which our perception joins into continuous arcs.
P. M. Roget, "Explanation of an Optical Deception in the Appearance of the Spokes of a Wheel Seen through Vertical Apertures," Philosophical Transactions of the Royal Society, 115, 1825 pp. 131–14.
W. B. Carpenter, "On the Zoetrope and its Antecedents," The Student and Intellectual Observer, 1, 1868 pp. 427–444.
J. L. Hunt, "The Roget Illusion, the Anorthoscope and the Persistence of Vision," American Journal of Physics, 71, 2003 pp. 774–777.
N. J. Wade and D. Heller, "Visual Motion Illusions, Eye Movements, and the Search for Objectivity," Journal of the History of the Neurosciences, 12, 2003 pp. 376–395.