SummaryA letter in which astronomer John Flamsteed expounded his unusual views about the causes of earthquakes survives in a number of drafts and copies. Though it was compiled in response to shocks felt in England in 1692 and Sicily in 1693, its relationship to the wide range of comparable theories current in the later seventeenth century must be considered. Flamsteed's suggestion that an ‘earthquake’ might be an explosion in the air was linked with contemporary thinking about the roles of sulphur (...) and nitre in earthquakes underground, and in combustion, respiration, and other processes. It reveals his concern with subjects other than astronomy and the influence of his continuing contact with members of the Royal Society; it also offers an early example of how seventeenth-century work on sulphur and nitre prepared the way for ‘airquake’ and electrical theories associated with the London earthquake of 1750. (shrink)