The now-disproved hypothesis of a medium for light propagation.
Historical account of the aether hypothesis and its refutation by Michelson-Morley.
This article has been archived. The aether theory was conclusively disproved by the Michelson-Morley experiment (1887) and superseded by special relativity.
The null result of the Michelson-Morley experiment was instrumental in motivating Einstein's 1905 postulates. For the modern successor, see article-special-relativity.