  These fluid dynamics video sequences show two Rayleigh-Taylor instability
experiments. The first video sequence shows an experiment where two layers of
uniform density are arranged such that the density of the upper layer is
greater than the density of the lower. The unstable interface between the two
layers is initially supported by a stainless steel barrier. With the removal of
the barrier, Rayleigh-Taylor instability results in the creation of a mixing
region, which grows with time. This growth accelerates until the mixing region
fills the entire tank. The second sequence shows Rayleigh-Taylor instability
when it is confined between two stable stratifications. Although initially the
growth of the mixing region accelerates, the stable stratification slows the
growth of the instability and brings it to a halt before it can fill the tank.
The stratifications are constructed of fresh and salt water and both
experiments have the same Atwood number. Visualisation of the upper surface of
the mixing layer was achieved by the use of fluorescent dye in the lower layer.
