On the passive gravitational mass
arXiv:physics/0109055
Abstract
A good candidate to the role of passive gravitational mass of a Schwarzschild's incompressible sphere is represented by the substantielle Masse of the sphere, which is larger than the active gravitational mass. Presumably this inequality has a general validity, i.e. it is not limited to the homogeneous spheres of incompressible fluids.
6 pages, PDF