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Magnetism of electrons is usually measured with the aid of so-called atom traps. The precision of measurements is to a large extend limited by the interaction of the electron and its mirror image charge induced by the electron in the electrodes of the trap. It is difficult to account for this interaction. Hans Dehmelt and his colleagues at the University of Washington succeeded in imprisoning 1000 electrons in an atom trap, thus producing a singlecomponent plasma consisting of negative charges only. The resulting droplet with spherical symmetry behaves like a point-like object with a charge and mass 1000 times those of a single electron. By studying such electron balls it is possible to account more accurately for the interaction of electrons with their mirror images. Electron balls may be useful in experimental plasma physics and many offer research areas. Source: Physics News Update, Number 241, physnews@ aip .org.