This experiment was performed by Albert Michelson (1852-1931) and Edward Morley (1838-1923) in 1887, and was intended to measure the effect that the luminiferous ether had on the passage of a beam of light passing through it. As the whole idea of the luminiferous ether was to draw a parallel between the way sound propagates through air and light propagates through space, it was predicted that ether wind moving at relative velocities would have an impact on the detected speed of light. (Michelson had earlier determined in an experiment at Annapolis that the speed of light was approximately 186,000 miles per hour.) The experiment involved attempting to detect the interference between two beams of light as split from one by a partial reflector to shine in perpendicular directions. Any difference in the speed of these two beams would result in an interference pattern at the detector.
Since the two beams were perpendicular, it was expected that they would be affected in different ways by the earth's rotation around the sun, and therefore its movement through the ether. Calculations showed that an ether windspeed of only one or two miles a second would have observable effects in this experiment, so if the ether windspeed was comparable to the earth's speed in orbit around the sun, the effects should have been easy to detect.
The experimental results, however, showed that there was no difference in speed between the two beams. Some time later, the experiment was redesigned to account for the rotation of the planet Earth. Again, the results were null. The scientists wondered if the ether was somehow held immobile by being close to the surface of the Earth, so the experiment was repeated on a high mountaintop in California. Again, the results of the experiment failed to show the effects of an ether wind. As a result, the experimenters had no choice but to conclude that their results, rather than proving the existence of the ether, provided strong evidence that it did not exist.
This experiment was one of the important foundations of Albert Einstein's theory of special relativity, which states that the speed of light is a universal constant. Michelson received the Nobel Prize in 1907 for his work, and was the first American to receive the Prize in science.