1275377 Portrait of Joseph Priestley. c.1789 (engraving) by English School, (18th century); Private Collection; (add.info.: Joseph Priestley FRS (1733 ??1804) was an 18th-century English theologian, Dissenting clergyman, natural philosopher, chemist, educator, and Liberal political theorist who published over 150 works. He is usually credited with the discovery of oxygen, having isolated it in its gaseous state, although Carl Wilhelm Scheele and Antoine Lavoisier also have a claim to the discovery;); Prismatic Pictures ; English, out of copyright.