Stanhope square demonstrator, c 1805.
© Science Museum / Science & Society Picture Library
The square type of Stanhope demonstrator, invented by Charles, 3rd Earl Stanhope (1753-1816) in about 1805, followed his circular demonstrators. The machine can be used to draw the correct conclusions from logical propositions, and allows the user to see the combined probability of two events ocurring. Stanhope was the first to attempt to solve logical problems by mechanical means.