gas [M17th] Gas is an invented word, coined in the 17th century by the Flemish chemist and physician Jan Baptista van Helmont (1577–1644), who was the first scientist to realize that there are gases other than air, and who discovered carbon dioxide. Van Helmont based the word on Greek khaos, *chaos, with the Greek chi replaced by the similar-sounding Dutch ‘g’. Although it was taken up by others, it did not really catch on until the 19th century, with earlier scientists like Robert Boyle preferring to think of gases as different types of *air. Gas for lighting or heating purposes dates from the late 18th century. The first experiments using coal-gas for lighting are said to have been made by the rector of Crofton, Dr Clayton, in about 1688; gas-lighting in its practical application was due to William Murdock (1754–1839). Gaslighting [M20th], the manipulating of someone into questioning their own sanity, comes from the 1944 film Gaslight, based on a play first performed in 1938, where this happens.