We start off again from quite special cases, which we have frequently used before. Let us consider a space-time domain in which no gravitational field exists relative to a reference-body
whose state of motion has been suitably chosen.
is then a Galileian reference-body as regards the domain considered, and the results of the special theory of relativity hold relative to
. Let us suppose the same domain referred to a second body of reference
', which is rotating uniformly with respect to