  The general relativistic notion of gravitational and inertial mass is
discussed from the general viewpoint of the tidal forces implicit in the
curvature and the Einstein field equations within ponderable matter. A simple
yet rigorously general derivation is given for the Tolman gravitational mass
viewpoint wherein the computation of gravitational mass requires both a rest
energy contribution (the inertial mass) and a pressure contribution. The
pressure contribution is extremely small under normal conditions which implies
the equality of gravitational and inertial mass to a high degree of accuracy.
However, the pressure contribution is substantial for conformal symmetric
systems such as Maxwell radiation, whose constituent photons are massless.
Implications of the Tolman mass for standard cosmology and standard high energy
particle physics models are briefly explored.
