FRACTAL MAGNETORESISTANCE. Canadian and Australian physicists have performed an experiment in which electrons enter a two-dimensional square enclosure (made from GaAs) through one tiny opening and leave by another. Voltage applied to an overlying electrode controls the electron flow. An additional electrode serves to squeeze off a circular region in the middle of the square, transforming the enclosure into a "Sinai billiard," named for Ya. G. Sinai who pioneered this research area in 1963. A plot of resistance through the device as a function of the applied magnetic field exhibits, for the first time in a billiards-type experiment, a fractal shape; that is, the resistance plot looks the same at several different magnifications (R.P.Taylor et al., Physical Review Letters, 10 March). The source of the geometry-induced fractal resistance is not known. This peculiar billiard table should provide an excellent laboratory for studying quantum chaos. (Nature, 13 March.)