systematic errors (Shankland's explanation is now widely accepted). 1958 – Cedarholm, Havens, and Townes use two masers frequency locked to each other and send the light in two directions. They receive the null result. The experiment is not as precise as earlier light-based MMX experiments, but demonstrates a novel setup that would become much more accurate in the future. 1964 – Jaseja, Javan, Murray and Townes repeat the earlier experiment with newer and much more precise masers. 1969 – Shamir and Fox repeat the MMX experiment with the "arms" in acrylic glass waveguides and a highly stable laser as the source. The experiment should detect a shift as small as ~0.00003 of a fringe, and none is measured. 1972 – R. S. Shankland admits he would not likely have given the effort to question Dayton Miller's work had it not been for Albert Einstein's "interest and encouragement." 1973 – Trimmer finds a null result in a triangular interferometer with one leg in glass. 1977 – Brecher repeats Zurhellen's experiment with binary pulsars, showing no difference in light speed to 2*10−9 1979 Brillet and Hall use the Townes setup with highly accurate lasers, demonstrating no drift to 3 parts in 1015. The experiment also demonstrates a leftover 17 Hz signal, but the authors assume it is linked to the laboratory. 1984 – Torr and Kolen find a cyclic phase shift between two atomic clocks, but the distance between is relatively short (0.5 km) and they are clocks of the less-precise rubidium type 1988 – Gagnon et al. measure one way light speed and detect no anisotropy 1990 – Hils and Hall repeat the Kennedy–Thorndike experiment with lasers, taking measurements over the period of a year. They find no shifting in 2 10−13 Krisher et al., Phys. Rev. D, 42, No. 2, pp. 731–734, (1990) use two hydrogen masers fixed to the earth and separated by a 21 km fiber-optic link to look for variations in the phase between them. They put an upper limit on the one-way linear anisotropy of 100 m/s. 1991 – Over a six-month period, Roland DeWitte finds, over a 1.5 km underground coaxial cable, a cyclic component in the phase drift between higher-precision caesium-beam clocks on more-or-less the same meridian; the period equals the sidereal day 2003 – Holger Mueller and Achim Peters carry out a Modern Michelson–Morley Experiment using Cryogenic Optical Resonators at Humboldt University, Berlin.