This quantity and big G are set equal to one in geometrized units. “One-way” measurements of this quantity are assumed to agree with “two-way” ones according to a common (20[1])synchronization convention. The Fizeau experiment measured a dragging coefficient of one minus one over n on this quantity. This quantity does not depend on a similar quantity of a Kennedy–Thorndike apparatus. The (*) isotropy of this quantity was shown in an experiment involving eleven-meter perpendicular arms with mirrors at each end. Special relativity requires that this quantity is the same in all inertial frames, implying that there is no luminiferous ether. For 10 points, the Michelson-Morley experiment showed that what quantity, symbolized c, is constant? ■END■