Thomas Vaughan (17 April 1621 − 27 February 1666) was a Welsh clergyman, philosopher, and alchemist, who wrote in English. He is now remembered for his work in the field of natural magic. He also published under the pseudonym Eugenius Philalethes. His influences included Johannes Trithemius (1462–1516), Heinrich Cornelius Agrippa (1486–1535), Michael Sendivogius (1566–1636), and Rosicrucianism (early 17th century). Life A Royalist clergyman from Brecon, Wales, Thomas was the twin brother of the poet Henry Vaughan, both being born at Newton, in the parish of St. Bridget's, in 1621. He entered Jesus College, Oxford, in 1638, and remained there for a decade during the English Civil War. Vaughan took part in the Battle of Rowton Heath in 1645. Although still based in Oxford, he became Rector of Llansantffraed (St Bridget), Wales, in 1640 and took up medical studies, motivated by the lack of doctors there. In 1650, however, Vaughan was evicted from the parish for his Royalist sympathies and alleged drunkenness. Vaughan later became involved in a plan by Robert Child to form a chemical club, with a laboratory and library, the main aim being to translate and collect chemical works. He married his wife Rebecca in 1651 and spent the next period of his life in London. His wife died in 1658. In 1661, Vaughan fell out with an alchemical collaborator, Edward Bolnest, over money matters and alleged broken promises, and the matter came to litigation after Bolnest had threatened violence. Vaughan was accused as part of this affair of spending "most of his time in the study of Naturall Philosophy and Chimicall Phisick". He is reported as having confessed that he had "long sought and long missed... the philosopher's stone." After the Restoration, he found a patron in Sir Robert Moray, with whom he fled from London to Oxford during the plague of 1665. Vaughan died at the house of Samuel Kem, at Albury, Oxfordshire. Works Although he did not practice medicine, Vaughan sought to apply his chemical skills to preparing medicines in the manner recommended by Paracelsus. He corresponded with Samuel Hartlib, who by 1650 was paying attention to Vaughan as author, and established a reputation with his book Anthroposophia Theomagica, a magico-mystical work. Vaughan was the author of tracts published under the pseudonym Eugenius Philalethes, as is now generally agreed. Vaughan was unusual amongst alchemists of the time in that he worked closely with his wife