Michelson-Morley experiment (A.A. Michelson, E.W. Morley; 1887): Probably the most famous null-experiment of all time, designed to confirm the existence of the proposed "lumeniferous aether" via which light waves were considered to propagate. As the Earth moves via this aether, a light beam fired in the Earth's direction of motion would lag at the back one fired sideways; where no aether consequence would be exist. This difference could be noticed with the utilization of an interferometer.
The experiment exhibited absolutely no aether shift at all, where one must have been quite detectable. Therefore the aether concept was harmed the reputation of as was the idea which one measures the velocity of light as being added vectorially to the velocity of the emitter.