  Firstly, I give the reason why is wrong my previously made assumption that
the volume integral over the pressure may not be zero in a system where the
gravitation plays no role in holding the system together. Secondly, in the
first nonlinear approximation I obtain the inner and outer Schwarzschild
solutions in harmonic and isotropic coordinates in two different ways. One way
is to start from standard solution and make the appropriate coordinate
transformation. The other way is to use the perturbation theory with elements
of Schwinger and Weinberg source approach. This latter method is applicable in
general case and it is useful to study all its peculiarities on known simple
example such as Schwarzschild solution. It turns out that this method is
simpler then S-metrics approach (previously made by Duff) and more informative
as it it shows which contribution comes from what region of space.
