ether

Any of a series of organic chemical compounds having an oxygen atom linking the carbon atoms of two hydrocarbon radical groups (general formula R-O-R′); also the common name for ethoxyethane C₂H₅OC₂H₅ (also called diethyl ether). This is used as an anaesthetic and as an external cleansing agent before surgical operations. It is also used as a solvent, and in the extraction of oils, fats, waxes, resins, and alkaloids.

Ethoxyethane is a colourless, volatile, inflammable liquid, slightly soluble in water, and miscible with ethanol. It is prepared by treatment of ethanol with excess concentrated sulphuric acid at 140°C/284°F.

ether (or aether)

In the history of science, a hypothetical medium permeating all of space. The concept originated with the Greeks, and has been revived on several occasions to explain the properties and propagation of light. It was supposed that light and other electromagnetic radiation – even in outer space – needed a medium, the ether, in which to travel. The idea was abandoned with the acceptance of relativity.

An important piece of evidence against the ether theory was the Michelson–Morley experiment, which showed that light travels at the same speed in the direction of the Earth's motion through space as it does at right angles to the motion. An ‘ether wind’ blowing past the Earth would be expected to affect the measured speed of light differently in the two directions. This and other experimental work that failed to detect any variation in the speed of light in a vacuum led Einstein to formulate his special theory of relativity.