[Gk. upper air.] A medium of extreme tenuity, which is assumed to pervade all space, and the interstices between the molecules of all bodies, whether solid, liquid, or gaseous. It is the medium by means of which light, heat, electricity, and magnetism are transmitted, it being claimed that diffused matter cannot convey these forces, and that a very rare substance, differing in character, is needed. Sulphuric ether is obtained by distilling strong alcohol and sulphuric acid, and is an exceedingly volatile and inflam-able body, dissolving fats, resins, and oils, and useful in removing grease stains. It is also used as an anaesthetic.