Complex sentence: Pearson experiment (1925) is a modified version of the Michelson-Morley experiment and the Sagnac-Interferometer which tests the theories of special relativity and luminiferous ether along the rotating frame of Earth.
Split into simpler sentences: Pearson experiment (1925) is a modified version of the Michelson-Morley experiment and the Sagnac-Interferometer. It measured the Sagnac effect due to Earth's rotation, and thus tests the theories of special relativity and luminiferous ether along the rotating frame of Earth.