Number 22 (Story #2), February 21, 1991 by Phillip F. Schewe and Ben Stein FRACTAL SPACE-FILLING BEARINGS: "Is it possible to tile an infinite strip with wheels rolling on each other such that the entire area is covered with wheels?" Writing in the 24 Dec. 1990 issue of Physical Review Letters, Hans Herrmann of CEN Saclay (France) describes his model solution to this problem, which essentially amounts to the iterative process of filling the space between three touching circles with an infinite number of smaller circles. The resultant tiling pattern (studied since antiquity) has a fractal shape. Herrmann and his colleagues further require that all of the wheels are turning and that any two touching wheels turn in opposite directions. If one imagines the wheels to be mechanical bearings, Herrmann's model would entail rolling friction but not gliding friction. This property, Herrmann believes, may make his model useful not only for the study of gears but also in the study of plate tectonics and turbulence. (Physics World, Feb. 1991.)