  We report results of dynamic light scattering measurements of the coherent
intermediate scattering function (ISF) of glasses of hard spheres for several
volume fractions and a range of scattering vectors around the primary maximum
of the static structure factor. The ISF shows a clear crossover from an initial
fast decay to a slower non-stationary decay. Ageing is quantified in several
different ways. However, regardless of the method chosen, the perfect "aged"
glass is approached in a power-law fashion. In particular, the coupling between
the fast and slow decays, as measured by the degree of stretching of the ISF at
the crossover, also decreases algebraically with waiting time. The
non-stationarity of this coupling implies that even the fastest detectable
processes are themselves non-stationary.
