[en] Light ray and free particle paths on a rotating disc are analysed. Previous work on this problem has been incomplete, often misleading and occasionally erroneous. It is shown how, due to the non-Euclidean nature of the spatial geometry of the disc, two apparently contradictory representations of photon trajectories on the disc are equivalent to each other. The velocity of light is calculated and shown to vary with position and with certain parameters describing the trajectory. The time of flight and distance travelled along the trajectory between two fixed reference points are shown to depend in general on the direction of flight (A → B or B → A) as well as on the position of the end points A and B. Finally an examination is made of the claim by previous workers that a contraction of length occurs in the radial direction. It is shown that this claim is without foundation and that the results of experiments by Davies and Jennison (J. Phys. A.; 8:1390 (1978)) are easily explained without resort to such a contraction. (author)