The result of the Michelson-Morley experiment was unavoidably revolutionary. The idea of an æther, through which optical effects were propagated with finite though great velocity, had grown up gradually, and had been rendered almost certain by the experimental establishment of the wave theory of light. Even on gravitational grounds, Newton himself regarded the existence of an æther as essential. Yet, in most relativistic discussions which deal with the point, he is relegated to the ranks of the direct actionists. His own words were emphatic. He said that, in his view, no one who was competent in matters of philosophic thought could be an advocate of distance action.