In general the spacetime or aether or vacuum velocity field and potential (the vector and scalar potentials) are obtained by solving Eqs. (1) and (2) simultaneously for given boundary conditions. The scalar potential is the spacetime enthalpy and the vector potential is the spacetime velocity field. There are also the wave equation (4) and the convective derivative equation (6). In a spacetime of constant pressure the spacetime velocity field needed for Newtonian gravitation is the simple equation (16), which implies Eq. (19) self consistently. For non Newtonian gravitation Eqs. (1) and (2) must be solved numerically and simultaneously for a given boundary condition.