The Problem of Relativity in reference to several bodies
§ 1. If the kinetic potential for the relative motion of two masses is written with an added constant asa close connexion with the relativity quadratic appears. The latter is in factwhere a modification of the primary formwhich shows an unaltered determinant. The condition in respect to the determinant, suggested, I believe, by Schwarzschild, is one which to me appears to give the most significant form to the results. From the dynamical standpoint we may regard it as imposing a counterpoise in the inertia coefficients to the modification introduced by the potential; or from a geometrical point of view we may regard it as minimizing the departure from the normal use of coordinates. An illuminating example of the loss of meaning that accompanies transformation in which this condition is disregarded is furnished by the isotropic form which is sometimes given to Einstein's quadratic.