Peter Mark Roget ( ; 18 January 1779 – 12 September 1869) was a British physician, natural theologian, lexicographer and founding secretary of The Portico Library. He is best known for publishing, in 1852, the Thesaurus of English Words and Phrases, a classified collection of related words. He also read a paper to the Royal Society about a peculiar optical illusion in 1824, which is often regarded as the origin of the persistence of vision theory that was later commonly used to explain apparent motion in film and animation. Early life Peter Mark Roget was born in Broad Street, Soho, London, the son of Jean (John) Roget (1751–1783), a Genevan cleric, and his wife, Catherine Romilly, sister of Samuel Romilly. After his father's death the family moved to Edinburgh in 1783 and he shortly began to study medicine at the University of Edinburgh, graduating in 1798. Samuel Romilly, who had supported his education, also introduced Roget into Whig social circles. Roget then attended lectures at London medical schools. Living in Clifton, Bristol, from 1798 to 1799, he knew Thomas Beddoes and Humphry Davy and frequented the Pneumatic Institute. Not making a quick start to a medical career, in 1802 Roget took a position as a tutor to the sons of John Leigh Philips, with whom he began a Grand Tour during the Peace of Amiens, travelling with a friend, Lovell Edgeworth, son of Richard Lovell Edgeworth. When the Peace abruptly ended he was detained as a prisoner in Geneva. He was able to bring his pupils back to England in late 1803 but Edgeworth was held in captivity until Napoleon fell on 6 April 1814. Medical career With the help of Samuel Romilly Roget became a private physician to William Petty, 1st Marquess of Lansdowne, who died in 1805. He then succeeded Thomas Percival at Manchester Infirmary and began to lecture on physiology. He moved to London in 1808 and in 1809 became a licentiate of the Royal College of Physicians. After an extended period of dispensary work and lecturing, in particular, at the Russell Institution and Royal Institution, he was taken onto the staff of the Queen Charlotte Hospital in 1817. He also lectured at the London Institution and the Windmill Street School. The politician, abolitionist, and legal reformer Sir Samuel Romilly committed suicide by cutting his throat, dying in Roget's presence, in 1818. Roget had been called by