  A suitable expression for hydrodynamic impulse in a compressible fluid is
deduced. The development of appropriate impulse formulation for compressible
Euler equations confirms the propriety of the hydrodynamic impulse expression
for a compressible fluid given here. Implications of the application of this
formulation to a compressible vortex ring are pointed out. A variational
characterization for an axisymmetric vortex system moving steadily in an ideal,
compressible fluid is discussed.
