From the basic hydrodynamical equations for non-viscous fluids, the second order wave equation in Eulerian coordinates has been expanded in terms of the velocity potential. Using the solution of this equation, the particle velocity , the pressure and the density in the Eulerian sense have been calculated down to second order terms. It is shown that when the wave is propagated the time averages of he excess pressure and density at the head of the wave train increase as the head is removed from the source of sound, and that the time averages of those in the field behind the head becomes negative. Thus the mass of the whole field containing the head is conserved. Also, the streaming in the acoustic field which has been previously studied by Eckart and Markham has been re-examined.
