  Collective excitations of a dilute Bose gas were probed above and below the
Bose-Einstein condensation temperature. The temperature dependencies of the
frequency and damping rates of condensate oscillations indicate significant
interactions between the condensate and the thermal cloud. Hydrodynamic
oscillations of the thermal cloud were observed, constituting first sound. An
antisymmetric dipolar oscillation of the thermal cloud and the condensate was
studied, representing the bulk flow of a superfluid through the normal fluid.
The excitations were observed in situ using non-destructive imaging techniques.
