William Jones was a Welsh mathematician, born in 1675 in the parish of Llanfihangel Tre'r Beirdd on the Isle of Anglesey. His father, John George Jones, was a small farmer, and William's early mathematical talent was spotted while he attended a charity school in Llanfechell. The Bulkeley family, local landowners who noticed his ability, helped find him work in London at a merchant's counting-house.
From 1695 he spent seven years teaching mathematics aboard Royal Navy ships, where his attention turned to navigation. He wrote 'A New Compendium of the Whole Art of Navigation' (1702), applying mathematics to the calculation of position at sea. He later settled in London as a mathematics teacher, both in the city's coffee houses and as a private tutor to the gentry, while also holding several government posts.
In 1706 Jones published 'Synopsis Palmariorum Matheseos', a work for beginners covering calculus and infinite series. In it he used the symbol π for the ratio of a circle's circumference to its diameter — the first time this notation appeared in print — adapting the Greek letter used for 'periphery' (περιφέρεια). His 1711 work on infinite series introduced the dot notation still used today for differentiation in calculus, and in 1731 he published 'Discourses on the Natural Philosophy of the Elements'.
Jones became a close friend of Sir Isaac Newton and Edmond Halley, and was elected a Fellow of the Royal Society in 1711, later serving as its Vice-President. He went on to edit and publish many of Newton's manuscripts and assembled one of the finest private libraries of scientific and mathematical books of his era. His son, also William, born in 1746, became a renowned philologist who established the historical links between Latin, Greek and Sanskrit, work that led to the concept of the Indo-European language family.