In all descriptions of the http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley" [Broken] I know of, the two arms of the interferometer are at right angles to each other. Does anyone know of an experiment which, just for completeness, tried other angles? If not, does anyone know of a reference with clear argumentation why it can be ruled out that other angles need to be tested? Not that I expect a different result for non-right angles, but (mathematical) proof is all the while better than guesstimation. Harald.