|Born||5 March 1574|
|Died||30 June 1660 (aged 86)|
|Alma mater||King's College, Cambridge|
|Known for||Slide rule|
Multiplication "×" sign
|Institutions||King's College, Cambridge|
|Notable students||John Wallis|
William Oughtred (// AWT-ed; 5 March 1574 – 30 June 1660) was an English mathematician and Anglican clergyman. After John Napier invented logarithms and Edmund Gunter created the logarithmic scales (lines, or rules) upon which slide rules are based, Oughtred was the first to use two such scales sliding by one another to perform direct multiplication and division. He is credited with inventing the slide rule in about 1622. He also introduced the "×" symbol for multiplication and the abbreviations "sin" and "cos" for the sine and cosine functions.
Oughtred was born at Eton in Buckinghamshire (now part of Berkshire), and educated at Eton College and King's College, Cambridge of which he became fellow. Being admitted to holy orders, he left the University of Cambridge about 1603, for a living at Shalford in Surrey; he was presented in 1610 to the rectory of Albury, near Guildford in Surrey, where he settled. He was rector of Albury for fifty years. His father was a writing-master at Eton College and taught him as well. Oughtred had a passion for mathematics, as he would stay up most nights and learn, while others were sleeping.  A primary source for his life is his address "To the English gentrie" in his Just Apologie of c. 1634, which contains autobiographical material.
Marriage and children
On 20 February 1606, he married Christsgift Caryll, (niece) of the Caryll family of Tangley Hall at Wonersh in Surrey, of which Lady Elizabeth Aungier (daughter of Sir Francis), wife of Simon Caryll 1607-1619, was matriarch and then dowager until her death in about 1650. The Oughtreds had twelve children, William, Henry, Henry (the first Henry died as a baby), Benjamin, Simon, Margaret, Judith, Edward, Elizabeth, Anne, George, and John. Two of his sons, Benjamin and John, shared Oughtred's interest in instruments and became watchmakers.
About 1628 he was appointed by the Earl of Arundel to instruct his son in mathematics. He corresponded with some of the most eminent scholars of his time, including William Alabaster, Sir Charles Cavendish, and William Gascoigne. He kept up regular contacts with Gresham College, where he knew Henry Briggs and Gunter.
He offered free mathematical tuition to pupils, who included Richard Delamain, and Jonas Moore, making him an influential teacher of a generation of mathematicians. Seth Ward resided with Oughtred for six months to learn contemporary mathematics, and the physician Charles Scarburgh also stayed at Albury; John Wallis, and Christopher Wren corresponded with him. Another Albury pupil was Robert Wood, who helped him get the Clavis through the press.
The invention of the slide rule involved Oughtred in a priority dispute with Delamain. They also disagreed on pedagogy in mathematics, with Oughtred arguing that theory should precede practice.
Interest in the occult
William Lilly, an eminent astrologer, knew Oughtred and claimed in his autobiography to have intervened on his behalf to prevent his ejection by Parliament in 1646;
"About this time, the most famous mathematician of all Europe, Mr. William Oughtred, parson of Aldbury in Surry, was in danger of sequestration by the Committee of or for plundered ministers; (Ambo-dexters they were;) several inconsiderable articles were deposed and sworn against him, material enough to have sequestered him, but that, upon his day of hearing, I applied myself to Sir Bolstrode Whitlock, and all my own old friends, who in such numbers appeared in his behalf, that though the chairman and many other Presbyterian members were stiff against him, yet he was cleared by the major number."
John Aubrey states that (despite their political differences) he was also defended by Sir Richard Onslow. He adds that Oughtred was an astrologer, and successful in the use of natal astrology, saying that he did not know why it should be effective, but believing that some "genius" or "spirit" assisted. According to Aubrey, Elias Ashmole possessed the original copy in Oughtred's handwriting of his rational division of the twelve houses of the zodiac, namely the text which George Wharton inserted in his Almanac for 1659. (The text of the English abstract of The Cabal of the Twelve Houses Astrological by "Morinus" (Jean-Baptiste Morin) appears over Oughtred's name with the date 16 October 1659 in Wharton's publications.) Aubrey suggests that Oughtred was happy to allow the country people to believe that he was capable of conjuring. He himself had seen a copy of Christopher Cattan's work on Geomancy annotated by Oughtred. He reported that Oughtred had told Bishop Ward and Elias Ashmole that he had received sudden intuitions or solutions to problems when standing in particular places, or leaning against a particular oak or ash tree, "as if infused by a divine genius", after having pondered those problems unsuccessfully for months or years.
Oughtred's name has been mentioned in purported histories of early freemasonry, a suggestion that Oughtred was present at Elias Ashmole's 1646 initiation going back to Thomas De Quincey. Oughtred expressed millenarian views to John Evelyn in 1655:
"Came that renowned mathematician, Mr. Oughtred, to see me, I sending my coach to bring him to Wotton, being now very aged. Among other discourse, he told me he thought water to be the philosopher's first matter, and that he was well persuaded of the possibility of their elixir; he believed the sun to be a material fire, the moon a continent, as appears by the late selenographers; he had strong apprehensions of some significant event to happen the following year, from the calculation of difference with the diluvian period; and added that it might possibly be to convert the Jews by our Saviour's visible appearance, or to judge the world; and therefore, his word was, Parate in occursum; he said Original Sin was not met with in the Greek Fathers, yet he believed the thing; this was from some discourse on Dr. Taylor's late book, which I had lent him."
Oughtred's name is remembered in the Oughtred Society, a group formed in the United States in 1991 for collectors of slide rules. It produces the twice-yearly Journal of the Oughtred Society and holds meetings and auctions for its members.
He published, among other mathematical works, Clavis Mathematicae (The Key to Mathematics), in 1631. It became a classic, reprinted in several editions, and used by Wallis and Isaac Newton amongst others. It was not ambitious in scope, but an epitome aiming to represent current knowledge of algebra concisely. It argued for a less verbose style of mathematics, with a greater dependence on symbols; drawing on François Viète (though not explicitly), Oughtred also innovated freely in symbols, introducing not only the multiplication sign as now used universally, but also the proportion sign (double colon ::). The book became popular around 15 years later, as mathematics took a greater role in higher education. Wallis wrote the introduction to his 1652 edition, and used it to publicise his skill as cryptographer; in another, Oughtred promoted the talents of Wren.
Other works were a treatise on navigation entitled Circles of Proportion, in 1632, and a book on trigonometry and dialling, and his Opuscula Mathematica, published posthumously in 1676. He invented a universal equinoctial ring dial of two rings.These three books are important in the development of basic and elementary mathematics.
- Clavis Mathematicae (1631) further Latin editions 1648, 1652, 1667, 1693; first English edition 1647.
- Circles of Proportion and the Horizontal Instrument (1632); this was edited by his pupil, William Forster.
- Trigonometria with Canones sinuum (1657).
The first edition of the Clavis Mathematicae was published in 1631 that consisted of 20 chapters and 88 pages that included algebra and several fundamentals of mathematics. Some changes were then added by Oughtred to the first edition, and a second and third edition were made in 1647 and 1648, having no preface and reducing the book by one chapter.
This book opens up with a discussion of the Hindu-Arabic notation of decimal fractions and later in the book, introduces multiplication and division sign abbreviations of decimal fractions. He also discusses two ways to do long division and introduces the "~" symbol, in terms of mathematics, expressing the difference between two variables.
Circles of Proportion and the Horizontal Instrument
In the Circles of Proportion and the Horizontal Instrument, Oughtred introduces the abbreviations for trigonometric functions. This book was originally in manuscript before it eventually became published. Also, the slide rule is discussed, an invention that was made by Oughtred which provided a mechanical method of finding logarithmic results. 
Trigonometria with Canones sinuum
Oughtred's invention of the slide rule consisted of taking a single "rule", already known to Gunter, and simplifying the method of employing it. Gunter required the use of a pair of dividers to lay off distances on his rule; Oughtred made the step of sliding two rules past each other to achieve the same ends. His original design of some time in the 1620s was for a circular slide rule; but he was not the first into print with this idea, which was published by Delamain in 1630. The conventional design of a sliding middle section for a linear rule was an invention of the 1650s.
At the age of 23, Oughtred invented the double horizontal sundial, now named the Oughtred type after him. A short description The description and use of the double Horizontall Dyall (16 pp.) was added to a 1653 edition (in English translation) of the pioneer book on recreational mathematics, Récréations Mathématiques (1624) by Hendrik van Etten, a pseudonym of Jean Leurechon. The translation itself is no longer attributed to Oughtred, but (probably) to Francis Malthus.
- How to Pronounce: Oughtred Society Retrieved 9 August 2018.
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- F. Willmoth, 'Oughtred, William (bap. 1575, d. 1660)', Oxford Dictionary of National Biography (2004).
- Smith, David E. (1958). History of Mathematics. Courier Corporation. p. 205. ISBN 9780486204307.
- Florian Cajori (1919). A History of Mathematics. Macmillan.
- "Oughtred, William (OTRT592W)". A Cambridge Alumni Database. University of Cambridge.
- WALLIS, P. J. (1968). "William Oughtred's 'Circles of Proportion' and 'Trigonometries'". Transactions of the Cambridge Bibliographical Society. 4 (5): 372–382. JSTOR 41154471.
- Karpinski, Louis C.; Cajori, Florian (1917). "William Oughtred, a Great Seventeenth-Century Teacher of Mathematics". The American Mathematical Monthly. 24 (1): 29–30. doi:10.2307/2972662. hdl:2027/bc.ark:/13960/t6tx40w87. JSTOR 2972662.
- (W. Oughtred), To the English gentrie, and all others studious of the mathematicks which shall bee readers hereof. The just apologie of Wil: Oughtred, against the slaunderous insimulations of Richard Delamain, in a pamphlet called Grammelogia, or the mathematicall ring, or mirisica logarithmorum projectio circularis (A. Mathewes, London ?1634). Full text at Umich/eebo (Reserved - Login only). Extracts in F. Cajori (1915) (Further reading).
- ODNB, and see Aubrey's Brief Lives, Ed. Oliver Lawson Dick (Ann Arbor, Michigan 1962), pp. 222–224.
- 1623 Harleian Visitation of Surrey, Harl Soc. Vol. XLIII (1899), pp. 88–89: cf. C. P. C. wills of John Machell, 1647; Elizabeth Machell, 1650/1656.
- "Oughtred biography". www-groups.dcs.st-and.ac.uk.
- Chisholm 1911.
- "Janus: Oughtred, William (? 1574-1660) mathematician". Janus.lib.cam.ac.uk. Retrieved 31 October 2012.
- "DSpace at Cambridge: Letter from William Gascoigne to William Oughtred". Dspace.cam.ac.uk. 13 June 2007. Retrieved 31 October 2012.
- "Loading..." www.compilerpress.atfreeweb.com.
- Helena Mary Pycior, Symbols, Impossible Numbers, and Geometric Entanglements: British Algebra Through the Commentaries on Newton's Universal Arithmetick (1997), p. 42.
- Toby Christopher Barnard, Cromwellian Ireland: English Government and Reform in Ireland 1649–1660 (2000), p. 223.
- Michelle Selinger, Teaching Mathematics (1994), p. 142.
- "The Galileo Project". Galileo.rice.edu. Retrieved 31 October 2012.
- "Parishes: Albury", in H.E. Malden (ed.), A History of the County of Surrey, Volume 3 (V.C.H./HMSO, London 1911), pp. 72-77 (British History Online, accessed 6 December 2018).
- Keith Thomas, Religion and the Decline of Magic (1973), p. 322 and 452n.
- William Lilly's History of his Life and Times, from the year 1602 to 1681 (Published London 1715), Reprint (Charles Baldwyn, London 1822), pp. 135-37 (Internet Archive).
- 'The Cabal of the Twelve Houses Astrological', collected in J. Gadbury (ed.), The Works of that Late Most Excellent Philosopher and Astronomer, Sir George Wharton, bar. collected into one volume (M.H. for John Leigh, London 1683), pp. 189-208. Full text at Oxford/Tcp (open).
- La Geomance du Seigneur Christofe de Cattan, Gentilhomme Genevoys. Livre non moins plaisant et recreatif. Avec la roüe de Pythagoras (Gilles Gilles, Paris 1558). Full text (page views) at Internet Archive.
- Oughtred may have possessed the English translation by Francis Sparry, The Geomancie of Maister Christopher Catton, a Booke no lesse pleasant and recreative, then of a wittie invention (London 1591).
- J. Aubrey, ed. R. Barber, Brief Lives (Boydell Press, Woodbridge 1982).
- Historico-Critical Inquiry into the Origins of the Rosicrucians and the Free-Masons
- E. g. William Wynn Westcott, The Rosicrucians, Past and Present, at Home and Abroad, p. 426.
- I.e. "Praeparare in occursum Dei tui, Israel" (Book of Amos, Chapter IV, v. 12): "Prepare to meet thy God, O Israel".
- 'Entry for 28 August 1655', in W. Bray (ed.), The Diary of John Evelyn, with a Biographical introduction by the editor, and a special introduction by Richard Garnett, LL.D., 2 vols (M. Walter Dunne, New York and London 1901), I, pp. 305-06 (Internet Archive, Retrieved 5 December 2018).
- "The Oughtred Society". The Oughtred Society. Retrieved 18 March 2015.
- "Brochure" (PDF). The Oughtred Society. Retrieved 18 March 2015.
- Helena Mary Pycior, Symbols, Impossible Numbers, and Geometric Entanglements: British Algebra Through the Commentaries on Newton's Universal Arithmetick (1997), p. 48.
- "Oxford Figures, Chapter 1: 800 years of mathematical traditions". Mathematical Institute – University of Oxford. 17 September 2007. Archived from the original on 26 October 2012. Retrieved 31 October 2012.
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- Stephen, Leslie, ed. (1889). . Dictionary of National Biography. 20. London: Smith, Elder & Co.
- Cajori, Florian (1915). "THE WORKS OF WILLIAM OUGHTRED". The Monist. 25 (3): 441–466. doi:10.5840/monist191525315. JSTOR 27900548.
- Ball, W. W. Rouse (1917). "Review of William Oughtred: a great Seventeenth-century Teacher of Mathematics". Science Progress (1916-1919). 11 (44): 694–695. JSTOR 43426914.
- "Slide Rules". Hpmuseum.org. Retrieved 31 October 2012.
- "The slide rule – a forgotten tool". Powerhouse Museum Collection. Retrieved 31 October 2012.
- "Harvard University – Department of History of Science". Dssmhi1.fas.harvard.edu. Archived from the original on 20 February 2012. Retrieved 31 October 2012.
- Heefer, Albrecht. "Récréations Mathématiques (1624) A Study on its Authorship, Sources and Influence" (PDF). logica.ugent.be.
- "Royal Museums Greenwich".
Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press..
- Cajori, Florian (1916). William Oughtred: A Great Seventeenth-Century Teacher of Mathematics. The Open Court Publishing Company.
- Florian Cajori (1915), "The Life of William Oughtred", The Open Court, Vol. XXIX no. 8 (Chicago, August 1915), p. 711, pp. 449-59 (pdf)
- Jacqueline Anne Stedall, Ariadne's Thread: The Life and Times of Oughtred's Clavis, Annals of Science, Volume 57, Issue 1 January 2000, pp. 27–60.
- O'Connor, John J.; Robertson, Edmund F., "William Oughtred", MacTutor History of Mathematics archive, University of St Andrews.
- Galileo Project page
- The Oughtred Society inspired by Oughtred and dedicated to the history and preservation of slide rules.
- Answers.com article with additional material on Oughtred.
- Account of Oughtred by John Aubrey
- William Oughtred's "Key of the Mathematics" (John Salusbury's English translation of Oughtred's "Clavis Mathematicae").