Ritz proposed in 1908 that SR was wrong, and that the speed of light would depend on the speed of the source according to Galilean addition of velocities, c+v. The review linked to from PF's sticky on the experimental basis of SR has a nice section on this: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#moving-source_tests These results are typically described in terms of a limit on k, where the speed of light is c+kv, k=0 being SR and k=1 being the Ritz theory. Early tests such as de Sitter's in 1913 http://en.wikipedia.org/wiki/De_Sitter_double_star_experiment were later realized to be problematic because of optical extinction. The earliest test they list that disproves k=1 and is not subject to optical extinction or other issues is a pair of experiments in 1964. It seems impossible to believe that the Ritz theory was really viable until 1964. Of course nobody believed it by then, and it was indirectly inconsistent with a gazillion other experiments, but was there really no direct disproof of k=1 until 1964? Were the early tests such as de Sitter's sufficient to falsify k=1, even given extinction? (De Sitter claimed k<.002, but he didn't consider extinction.) Historically, what was the first direct test that ruled out the Ritz theory?