Also, please, read the landmark paper "An Established Numerical Method Applied to Geophysics" EOS, Vol. 93, No. 29, 17 July 2012, by Jamesina J. Simpson.
Why Maxwell Couldn’t Explain Gravity
It is also intuitively immediately apparent that without a stress tensor for the static gravitational field, the Newtonian forces cannot be derived from an energy tensor. Also, if the energy-momentum conservation concept is not applied to the metric field, it loses all physical value. A. Einstein to M. Besso, August 1918
I have to do a link between the potential vector and position in space-time by introducing a new universal constant which "the mechanical impedance of vacuum" .The electromagnetic field and the gravitational field are unified.