Light exhibits wavelike behaviors, like reflection, refraction, and diffraction, but can also travel through a space from which all air has been removed.
To nineteenth-century scientists, these observations were conflicting, because waves were only known to travel within a medium, like air or water.
To explain the discrepancy, scientists postulated a hypothetical medium that they called the "ether." The ether was thought to pervade, or penetrate, any enclosure with ease as well as to exist in the vacuum of space.
In the late 1800s, physicists Albert Michelson and Edward Morley designed an experiment to ascertain the ether's existence.
Albert Michelson