Nonstationary hydrodynamic flow and Lie's theorem on finite continuous groups

The one-parameter group property of a continuous and stationary hydrodynamic flow is taken to be an intrinsic property of the flow. The specification of having the group property prevail for references with respect to which the same flow may not be stationary demands a group representation applicable to stationary as well as to non-stationary flow. A space-time realization of the group meets that requirement. The group parameter of this realization is a domain-scalar of space-time, which is not in general identifiable with proper time, unless the flow is geodetic. The implications of a kinematics based on this group parameter instead of on proper time, is investigated in some detail, in particular, for the case where the two parameters differ; that is, non-geodetic flow.