Remarks Concerning Einstein's Theory of Gravitation

In his interesting paper Outline of a Generalized Theory of Relativity etc.¹ Mr. Einstein says that by introducing a variable speed of light he has broken out of “the confines of the theory known at present as the theory of relativity,” and also on other occasions he frequently contrasts his theory with the “old theory of relativity.” To someone who immerses himself sufficiently deeply in the development it may become clear in what respect Mr. Einstein can speak of a new relativity; nevertheless, one may suppose that the cited passages may lead a more cursory reader to the wrong view, that one is really dealing here with a break with the theory of relativity as presently known. It is therefore certainly not without interest to present below, using methods recently developed by me in a larger work about the theory of matter,² which strictly followed Minkowski's concept of the principle of relativity, a general theory of gravitation with a tensor potential, which includes Einstein's theory as a special case. Contrary to the rather inscrutable formulas of Einstein, the methods I use have the advantage that they yield clearly transparent expressions. In this fashion, it then becomes possible to comprehend the nature of Einstein's theory better, and in particular to clarify the so-called generalization of the principle of relativity, and furthermore to compare it with the theory of gravitation suggested by myself³ and with that | of Nordström,⁴ which deviates only slightly from mine.