If we substitute the right-hand side for the left-hand side in the former integral, and put
outside the sign of integration, we obtain,
We see, therefore, that the generalized conception of the energy tensor is in agreement with our former result.
The Eulerian Equations for Perfect Fluids. In order to get nearer to the behaviour of real matter we must add to the energy tensor a term which corresponds to the pressures. The simplest case is that of a perfect fluid in which the pressure is determined by a scalar
. Since the tangential stresses
