milanković did two papers on relativity. he wrote his first paper "on the theory of michelson's experiment" in 1912. he was doing research in this theory as of 1924. in fact his papers on this matter were on special relativity and both are on michelson experiment (now known as michelson–morley experiment) which gave the strong evidence against aether theory. in the light of the michelson experiment he discussed on the validity of the second postulate of special theory of relativity, that the speed of light is the same in all reference frame.