Attempt to detect the velocity of the Earth with respect to ether, a hypothetical medium in space formerly proposed to carry light waves.
It was first performed in Berlin in 1881 by A.A. Michelson and refined in the U.S. in 1887 by Michelson and Edward W. Morley (1838–1923). The procedure assumed that if the speed of light were constant with respect to the ether, the motion of the Earth could be detected by comparing the speed of light in the direction of the Earth's motion and the speed of light at right angles to the Earth's motion. No difference was found, and the result discredited the ether theory. As a result, Albert Einstein proposed in 1905 that the speed of light is a universal constant.