The Michelson-Morley experiment is one of the most famous and significant experiments in the history of physics. It was first performed in 1881 by Abraham Michelson in Potsdam and in early July 1887, in an improved version, together with Edward Morley in Cleveland, Ohio. In the late 19th century, theoretical physics assumed that, much like waves in water and sound waves, light waves were also propagated through a medium. This medium was referred to as the luminiferous aether. The Michelson-Morley experiment was aimed at detecting the aether and its velocity relative to the earth and its orbit around the sun. The attempt at providing evidence of aether failed. Against their expectations, the experiment (which was not easy, given the small orbital velocity compared to the speed of light) returned what was considered a null result for this velocity, independently of the time of year. Not until 1905 was the significance of this result understood – with the aid of the theory of relativity, which dispensed with the aether hypothesis.