William Jones (mathematician)

William Jones, a Welsh mathematician born in 1675, is chiefly remembered for introducing the Greek letter π to represent the ratio of a circle’s circumference to its diameter. He first used this symbol in his 1706 work *Synopsis Palmariorum Matheseos*, a beginner’s guide that also covered differential calculus and infinite series, following earlier shorthand for the Greek word for periphery. Jones’s mathematical talents were recognized early: raised in the parish of Llanfihangel Tre’r Beirdd on Anglesey, he attended a charity school in Llanfechell, where a local landowner, Lord Bulkeley, arranged for him to work in a London merchant’s counting-house. Before settling ashore, Jones served at sea from 1695 to 1702, teaching mathematics aboard Navy ships and developing a deep interest in navigation. He published *A New Compendium of the Whole Art of Navigation* in 1702, applying mathematics to determine position at sea. After his voyages, he taught mathematics in London—both in coffee houses and as a private tutor to George Parker, son of the future Earl of Macclesfield. His 1711 work *Analysis per quantitatum series, fluxiones ac differentias* introduced the dot notation for differentiation in calculus. Jones became a fellow of the Royal Society in November 1711, later serving as its vice-president, and was a close friend of Sir Isaac Newton and Sir Edmund Halley. He edited and published many of Newton’s manuscripts, amassing one of the greatest private libraries of scientific and mathematical works, which he bequeathed to the Earl of Macclesfield. Jones married twice; his second wife, Mary Nix, bore him two children, including a son, also named William, who became a renowned philologist linking Latin, Greek, and Sanskrit. Jones died in July 1749.