  A mass distribution is analyzed in terms of classical gravitational field
theory. Newton's law of gravitation is consistently applied on the assumption
that the equivalence of energy and mass according to Einstein's theory of
relativity is valid for gravitational fields as well. Different from standard
approaches the gravitational field, via its associated field energy, is handled
as a source of gravitation by itself. Starting from these principles a
gravitational self-shielding phenomenon is derived as a common characteristic
of all mass/energy distributions. Moreover, it is demonstrated that even in the
absence of any stimulating mass the existence of independent static
gravitational fields is fully consistent with Newton's law of gravitation as
long as the equivalence of energy and mass is respected. From a distance such
gravitational fields appear as negative masses.
