SummaryThe Science Museum, London, recently acquired some circular logic demonstrators by Charles Mahon, 3rd Earl Stanhope. A study of what exists of Stanhope's unpublished book, notes and letters on the subject allows the development of his demonstrators to be traced. A consideration of Stanhope's characters and interests reveals an Enlightenment figure with aspirations consonant with that era, the logic demonstrators representing the material culmination of his ideals. Yet the demonstrators were not made public during his lifetime, and the final form (...) was greeted with derision 60 years after his death. (shrink)