The Determination of the Potentials in the General Theory of Relativity, with Some Remarks about the Measurement of Lengths and Intervals of Time and about the Theories of Weyl and Eddington

It was remarked some years ago by Kretschmann 2) that from observations solely concerning the course of rays of light and the motion of material particles, the values of the potentials g ab which characterize a gravitation-field can be so far deduced that only a constant factor remains undetermined. He showed, in fact, that, if two sets of values g ab and ḡ ab are in agreement with these observations, the ratio ḡ ab /g ab must be the same for all suffixes a and b, and independent of the coordinates.