  Recently, the topic of Casimir repulsion has received a great deal of
attention, largely because of the possibility of technological application. The
general subject has a long history, going back to the self-repulsion of a
conducting spherical shell and the repulsion between a perfect electric
conductor and a perfect magnetic conductor. Recently it has been observed that
repulsion can be achieved between ordinary conducting bodies, provided
sufficient anisotropy is present. For example, an anisotropic polarizable atom
can be repelled near an aperture in a conducting plate. Here we provide new
examples of this effect, including the repulsion on such an atom moving on a
trajectory nonintersecting a conducting cylinder; in contrast, such repulsion
does not occur outside a sphere. Classically, repulsion does occur between a
conducting ellipsoid placed in a uniform electric field and an electric dipole.
The Casimir-Polder force between an anisotropic atom and an anisotropic
dielectric semispace does not exhibit repulsion. The general systematics of
repulsion are becoming clear.
