Birthday of John Venn (1834)

John Venn introduced the eponymous diagrams to visualise set operations. His 1881 book ‘Symbolic Logic’ used overlapping circles to show intersections, unions, and complements. Venn diagrams are now standard in teaching logic, probability, and database theory. Venn was also a priest and historian, and he built a machine for bowling cricket balls. The diagrams were not original to him – Leibniz and Euler used similar ideas – but Venn systematised them and made them popular.