  Three weeks after this address, Milne spoke on related topics at the monthly meeting of the Royal Astronomical Society. His main point was that theories differed only insofar as their concepts could be cashed out in observations deduced from them. Eddington took strong exception to Milne’s arguments, claiming in response that kinematic relativity and relativistic cosmology differed more importantly in their ontology than in their consequences. Eddington was especially concerned with differences in the spacetime-geometry each theory ascribed to the world. For Eddington and his colleagues, the equivalence of gravitation and spacetime geometry was a genuine reality, a feature of the physical world, just as real as suns and moons and stars.