In the late 19th century, for example, the idea that light-waves have a physical medium called the luminiferous ether would have been best thought of as a neutral analogy with water and sound waves. Eventually, due to a null result in the Michelson–Morley and Trouton–Noble experiments, as well as other similar experiments, this analogy came to be accepted as a negative analogy - we now accept that light has no physical medium, unlike sound and water waves. The discovery of this negative analogy led to further advances, including the unification of electromagnetic theory with optics, and the eventual creation of new and more informative models of light.