Relativistic Newton and Coulomb Laws
  The relativistic equations for the electromagnetic and gravitation interactions are similar: The only Lagrangian equation is the equation with Lorentz force. The potential satisfies the wave equation with the right - hand side proprtional to the velocity of another particle multiplied by the delta - function concentrated at the position of another particle. If the interaction propagates at the speed of light, then the wave equation has the unique solution: the Lienard - Wiechert potential. The Maxwell equations are completely defined by the obtained relativistic Coulomb law. The Coulomb law and the Newton gravity law differ from each other only in the choice of the constants. If we choose in Coulomb law the electric charges equal to the masses and choose the interaction constant of another sign, then we get Newton gravity law. If we choose in the relativistic Coulomb law the electric charges equal to the masses and choose the interaction constant of another sign, then we get the relativistic Newton gravity law. 
Yury M. Zinoviev