  Maxwell's equations comprise both electromagnetic and gravitational fields.
The transverse part of the vector potential belongs to magnetism, the
longitudinal one is concerned with gravitation. The Coulomb gauge indicates
that longitudinal components of the fields propagate instantaneously. The
delta-function singularity of the field of the divergence of the vector
potential, referred to as the dilatation center, represents an elementary agent
of gravitation. Viewing a particle as a source or a scattering center of the
point dilatation, the Newton's gravitation law can be reproduced.
