The Mysterious Case of James Watt's '"1785" Steam Indicator': Forgery or Folklore in the History of an Instrument?

Abstract

Investigation of nineteenth-century accounts, and displays, of a recording steam indicator attributed to James Watt and dated 1785 led to the discovery of an instrument engraved with that date. Other sources show that the first recording indicator in fact dates from the mid-1790s. The paper investigates the provenance of the '1785 recording indicator', its origins in either forgery or folklore, and discusses its significance with regard to ideas about James Watt's understanding of the nature of heat and the operation of the steam engine.