The Physical Significance of Birkhoff's Gravitational Equations
Phys. Rev. 72, 229 – Published 1 August, 1947
DOI: https://doi.org/10.1103/PhysRev.72.229
Abstract
Birkhoff's gravitational equations are put in terms of in place of the local time used by him. The transformed equations show that Lorentzian mass has been used, and to the Newtonian attractive force is added a force normal to the direction of motion, times the component of the gravitational force normal to the motion.