The timeline of luminiferous aether (light-bearing aether) or ether as a medium for propagating electromagnetic radiation begins in the 18th century. The aether was assumed to exist for much of the 19th century—until the Michelson–Morley experiment returned its famous null result. Further experiments were in general agreement with Michelson and Morley's result. By the 1920s, most scientists rejected the aether's existence. Timeline Early experiments 4th-century BC – Aristotle publishes Physics, in which the aether is briefly described as being an element lighter than air that surrounds celestial bodies. He describes the aether in relation to other elements - aether is lighter than air and is located above it, whereas air is lighter than water, and water is lighter than earth. In Aristotle's view, each element returns to its proper place when displaced, which explains why air rises, why earth and water fall, and why the heavens remain in place. 16th century: Robert Boyle was a proponent of an aether hypothesis. According to Boyle, the aether consists of subtle particles, one sort of which explains the absence of vacuum and the mechanical interactions between bodies, and the other sort of which explains phenomena such as magnetism (and possibly gravity) that are, otherwise, inexplicable on the basis of purely mechanical interactions of macroscopic bodies. 1690 - Christiaan Huygens's Treatise on Light hypothesized that light is a wave propagating through an aether. 1704 – Isaac Newton publishes Opticks, in which he proposes a particle theory of light. This had trouble explaining diffraction, so he adds a "fudge factor," claiming that an "Aethereal Medium" is responsible for this effect, and going further to suggest it might be responsible for other physical effects such as heat. 1727 – James Bradley measures stellar aberration for the first time, proving (again) that light has a finite speed as well as that the Earth is moving. 1818 – Augustin Fresnel introduces the wave theory of light, which proposes light is a transverse wave travelling in an aether, thereby explaining how polarization can exist. It is important to note that both Newton's particle theory and Fresnel's wave theory both assume an aether exists, albeit for different reasons. From this point on, no one even seems to question its existence. 1820 – Discovery of Siméon Poisson's "Bright Spot", supporting the Wave Theory. 1830 – Fresnel develops a formula for predicting and measuring aether dragging by massive objects, based on a