Albert Abraham MichelsonThe speed of light measured by using Foucault's method "The grand underlying principles have been firmly established...further truths of physics are to be looked for in the sixth place of decimals." Michelson conducted experiments with Edward W. Morely to determine the existence of ether. Ether was a hypothetical all-pervasive medium which was believed to extend throughout the universe. He built an interferometer, which was a device used for light wave interference and measured the differences in velocity of two light beams. He observed that the interferometer, using two mirrors would split a beam of light in two and sent them along perpendicular paths and brought them back together again. The measurements of differences in velocity of light were determined by this experiment. Michelson was considered the first person to use this device to measure the size of the ether. In 1920, he used a six-meter interferometer attached to a 254-centimeter telescope to successfully measure the diameter of Betelgeuse (Alpha Orionis) at 386,160,000 kilometers. Here is an image of the interferometer
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