It will be seen that Jones's career fell outside Wales, and his contacts with Welsh concerns were casual, though none the less interesting. It seems that Richard alone of the Morrises knew him personally, though Lewis in 1749 (see above) wrote to him. But in 1747 (Morris Letters, 129), we find Richard suggesting that Jones should propose Lewis for membership of the Royal Society — a service which he had already rendered to Moses Williams (1685-1742) (q.v.). When Richard Morris's edition of the Welsh Bible appeared (1746), it included two maps, ‘a gift of William Jones, F.R.S., to the Welsh people.’ On the death of Moses Williams, his widow sold his books and manuscripts to his friend William Jones, and Richard Morris took on the cataloguing of the manuscripts. But when Jones in his turn d., the manuscripts went, under his will, to his pupil the 2nd earl Macclesfield, who refused Morris further access to them. The earl talked of giving them to the British Museum, but in fact they remained at Shirburn for some 150 years — Angharad Llwyd (q.v.) tells us that she too offered to complete the catalogue but was told that the manuscripts ‘were not worth the trouble.’ But in 1899 they were bought by Sir John Williams (q.v.) and catalogued by J. Gwenogvryn Evans (q.v.) — they are today (with Richard Morris's notes and indexes) in the National Library of Wales.

He was born in 1674 or 1675; the same year as the father of the Morris brothers of Anglesey (see Lewis Morris, DWB, 661, Richard Morris, DWB, 663-4, William Morris, DWB, 666-7). He d. 1 July, not 3 July, 1749, and was buried in St. Paul's church, Covent Garden on 7 July 1749. He was married twice: (1) to the widow of the merchant who employed him when he went to London. This might explain how he came by the money which he later lost; and (2) to Mary Nix on 17 Apr. 1731 when he was 56 and she was 25.

He left his mark on mathematics in several ways. The use of the symbol π to designate the ratio of the circumference of a circle to its diameter first appeared in his book Synopsis Palmarorium Matheseos (1706) and it was he, in his editions of Newton's works who used the dot as the differential sign in the calculus. In one of his papers in the Trans. of the Royal Society he created a rule for compound interest and many mathematicians of the period sought his opinion of their work.

In his will he left his library of some 15,000 works and over 50,000 pages of manuscripts, including hundreds of pages refering to those whom he knew and several of Newton's MSS. to the 3rd Earl Macclesfield, most of which remain in the earl's home, Shirburn Castle.