  Low frequency dielectric measurements on plexiglass (PMMA) show that cooling
and heating the sample at constant rate give an hysteretic dependence on
temperature of the dielectric constant $\epsilon$. A temporary stop of cooling
produces a downward relaxation of $\epsilon$. Two main features are observed i)
when cooling is resumed $\epsilon$ goes back to the values obtained without the
cooling stop (i.e. the low temperature state is independent of the cooling
history) ii) upon reheating $\epsilon$ keeps the memory of the aging history
({\it Memory}). The analogies and differences with similar experiments done in
spin glasses are discussed.
