View source for Biography:John Wallis

{{Short description|English mathematician (1616–1703)}}
{{Other people|John Wallis}}
{{Infobox scientist
|name              = John Wallis
|image             = John Wallis by Sir Godfrey Kneller, Bt.jpg
|caption           =
|birth_date        = {{OldStyleDate|3 December|1616|23 November}}
|birth_place       = Ashford, Kent, England
|death_date        = {{nowrap|{{OldStyleDateNY|{{death date and age|1703|11|8|1616|12|3|df=y}}|28 October 1703}}}}
|death_place       = {{nowrap|Oxford, Oxfordshire, England}}
|nationality       = English
|field             = [[Mathematics]]
|work_institutions = {{hlist|[[Organization:Queens' College, Cambridge|Queens' College, Cambridge]]|[[Organization:University of Oxford|University of Oxford]]}}
|education         = Felsted School, {{nowrap|Emmanuel College, Cambridge}}
|academic_advisors = William Oughtred
|notable_students  = William Brouncker
|known_for         = [[Wallis product]]<br />[[Infinity|Inventing the symbol {{resize|150%|∞}}]]<br />Extending [[Cavalieri's quadrature formula]]<br />Coining the term "[[Physics:Momentum|momentum]]"<ref>Joseph Frederick Scott, ''The mathematical work of John Wallis (1616-1703)'', Taylor and Francis, 1938, p. 109.</ref>
|influences        =
|influenced        =
|prizes            =
|signature         =
|footnotes         =
}}

'''John Wallis''' ({{IPAc-en|ˈ|w|ɒ|l|ɪ|s}};<ref>[http://www.dictionary.com/browse/wallis ''Random House Dictionary''].</ref> {{lang-la|Wallisius}}; {{OldStyleDate|3 December|1616|23 November}}{{spnd}}{{OldStyleDate|8 November|1703|28 October}}) was an English clergyman and [[Biography:Mathematician|mathematician]] who is given partial credit for the development of infinitesimal calculus. Between 1643 and 1689 he served as chief cryptographer for Parliament and, later, the royal court.<ref>{{cite journal|author=Smith, David Eugene|title=John Wallis As a Cryptographer|journal=Bulletin of the American Mathematical Society|year=1917|volume=24|issue=2|pages=82–96|mr=1560009|doi=10.1090/s0002-9904-1917-03015-7|doi-access=free}}</ref> He is credited with introducing the [[Symbol|symbol]] ∞ to represent the concept of [[Infinity|infinity]].<ref name=EB1911/> He similarly used 1/∞ for an [[Infinitesimal|infinitesimal]]. John Wallis was a contemporary of [[Biography:Isaac Newton|Newton]] and one of the greatest intellectuals of the early renaissance of [[Mathematics|mathematics]].<ref>{{Cite journal|last=Kearns|first=D. A.|date=1958|title=John Wallis and complex numbers|journal=The Mathematics Teacher|volume=51|issue=5|pages=373–374|jstor=27955680}}</ref>

== Biography ==

=== Educational background ===
* Cambridge, M.A., Oxford, D.D.
* Grammar School at Tenterden, Kent, 1625–31.
* School of Martin Holbeach at Felsted, Essex, 1631–2.
* Cambridge University, Emmanuel College, 1632–40; B.A., 1637; M.A., 1640.
* D.D. at Oxford in 1654

=== Family ===

On 14 March 1645{{which calendar?|date=September 2019}} he married '''Susanna Glynde''' ({{circa|1600}} – 16 March 1687).{{which calendar?|date=September 2019}} They had three children:
# Anne Blencoe (4 June 1656 – 5 April 1718),{{which calendar?|date=September 2019}} married Sir John Blencowe (30 November 1642 – 6 May 1726){{which calendar?|date=September 2019}} in 1675, with issue<ref>Joan Thirsk, 'Blencowe , Anne, Lady Blencowe (1656–1718)’, Oxford Dictionary of National Biography, Oxford University Press, Oct 2005; online edn, Jan 2007 [http://www.oxforddnb.com/view/article/41326, accessed 16 Nov 2016]</ref>
# '''John Wallis''' (26 December 1650 – 14 March 1717),{{which calendar?|date=September 2019}}<ref>[http://www.historyofparliamentonline.org/volume/1690-1715/member/wallis-john-1650-1717 WALLIS, John (1650-1717), of Soundness, Nettlebed, Oxon. | History of Parliament Online<!-- Bot generated title -->]</ref> MP for Wallingford 1690–1695, married Elizabeth Harris (d. 1693) on 1 February 1682,{{which calendar?|date=September 2019}} with issue: one son and two daughters
# '''Elizabeth Wallis''' (1658–1703<ref>[http://emlo.bodleian.ox.ac.uk/profile/person/e4d46f16-a83a-4375-bbc1-88e939f95622 Early Modern Letters Online : Person<!-- Bot generated title -->]</ref>), married William Benson (1649–1691) of Towcester, died with no issue

=== Life ===
John Wallis was born in Ashford, Kent. He was the third of five children of Reverend John Wallis and Joanna Chapman. He was initially educated at a school in Ashford but moved to James Movat's school in Tenterden in 1625 following an outbreak of [[Medicine:Bubonic plague|plague]]. Wallis was first exposed to mathematics in 1631, at Felsted School (then known as Martin Holbeach's school in Felsted); he enjoyed maths, but his study was erratic, since "mathematics, at that time with us, were scarce looked on as academical studies, but rather mechanical" (Scriba 1970). At the school in Felsted, Wallis learned how to speak and write [[Social:Latin|Latin]]. By this time, he also was proficient in [[Social:French language|French]], [[Social:Greek language|Greek]], and [[Social:Hebrew language|Hebrew]].<ref name=":0">{{Cite journal|last=Yule|first=G. Udny|date=1939|title=John Wallis, D.D., F.R.S.|journal=Notes and Records of the Royal Society of London|volume=2|issue=1|pages=74–82|jstor=3087253|doi=10.1098/rsnr.1939.0012}}</ref> As it was intended he should be a doctor, he was sent in 1632 to Emmanuel College, Cambridge.<ref>{{acad|id=WLS632J|name=Wallys, John}}</ref> While there, he kept an ''act'' on the doctrine of the circulation of the blood; that was said to have been the first occasion in Europe on which this theory was publicly maintained in a disputation. His interests, however, centred on mathematics. He received his Bachelor of Arts degree in 1637 and a Master's in 1640, afterwards entering the priesthood. From 1643 to 1649, he served as a nonvoting scribe at the Westminster Assembly. He was elected to a fellowship at [[Organization:Queens' College, Cambridge|Queens' College, Cambridge]] in 1644, from which he had to resign following his marriage.

Throughout this time, Wallis had been close to the Parliamentarian party, perhaps as a result of his exposure to Holbeach at Felsted School. He rendered them great practical assistance in deciphering Royalist dispatches. The quality of cryptography at that time was mixed; despite the individual successes of mathematicians such as [[Biography:François Viète|François Viète]], the principles underlying cipher design and analysis were very poorly understood. Most ciphers were ad hoc methods relying on a secret [[Algorithm|algorithm]], as opposed to systems based on a variable [[Key (cryptography)|key]]. Wallis realised that the latter were far more secure – even describing them as "unbreakable", though he was not confident enough in this assertion to encourage revealing cryptographic algorithms. He was also concerned about the use of ciphers by foreign powers, refusing, for example, Gottfried Leibniz's request of 1697 to teach Hanoverian students about cryptography.<ref>{{citation|first=David|last=Kahn|title=The Codebreakers: The Story of Secret Writing|year=1967|place=New York|publisher=Macmillan|lccn=63016109|page=169}}</ref>

Returning to London – he had been made chaplain at St Gabriel Fenchurch in 1643 – Wallis joined the group of scientists that was later to evolve into the Royal Society. He was finally able to indulge his mathematical interests, mastering William Oughtred's ''Clavis Mathematicae'' in a few weeks in 1647. He soon began to write his own treatises, dealing with a wide range of topics, which he continued for the rest of his life. Wallis wrote the first survey about mathematical concepts in England where he discussed the Hindu-Arabic system.<ref name="ReferenceA">4</ref>

Wallis joined the moderate Presbyterians in signing the remonstrance against the execution of Charles I, by which he incurred the lasting hostility of the Independents. In spite of their opposition he was appointed in 1649 to the Savilian Chair of Geometry at Oxford University, where he lived until his death on {{OldStyleDate|8 November|1703|28 October}}. In 1650, Wallis was ordained as a minister. After, he spent two years with Sir Richard Darley and Lady Vere as a private [[Religion:Chaplain|chaplain]]. In 1661, he was one of twelve Presbyterian representatives at the Savoy Conference.

Besides his mathematical works he wrote on [[Religion:Theology|theology]], [[Logic|logic]], English grammar and philosophy, and he was involved in devising a system for teaching a deaf boy to speak at Littlecote House.<ref>{{cite news|title=Find could end 350-year science dispute|url=http://news.bbc.co.uk/1/hi/health/7511446.stm|access-date=5 May 2018|publisher=BBC|date=26 July 2008}}</ref> William Holder had earlier taught a deaf man, Alexander Popham, to speak "plainly and distinctly, and with a good and graceful tone".<ref>W. Holder, W. (1668). "Of an Experiment, Concerning Deafness". ''Philosophical Transactions of the Royal Society'' 3, pp. 665–668.</ref> Wallis later claimed credit for this, leading Holder to accuse Wallis of "rifling his Neighbours, and adorning himself with their spoyls".<ref>Holder, ''Philosophical Transactions of the Royal Society'', supplement, 10.</ref>

==== Wallis' appointment as Savilian Professor of Geometry at the Oxford University ====

The Parliamentary visitation of Oxford that began in 1647 removed many senior academics from their positions, including (in November 1648){{which calendar?|date=September 2019}} the Savilian Professors of Geometry and Astronomy. In 1649 Wallis was appointed as Savilian Professor of Geometry. Wallis seems to have been chosen largely on political grounds (as perhaps had been his Royalist predecessor Peter Turner, who despite his appointment to two professorships never published any mathematical works); while Wallis was perhaps the nation's leading cryptographer and was part of an informal group of scientists that would later become the Royal Society, he had no particular reputation as a mathematician. Nonetheless, Wallis' appointment proved richly justified by his subsequent work during the 54 years he served as Savilian Professor.<ref>[https://www.maths.ox.ac.uk/system/files/media/John%20Wallis.pdf John Wallis: Time-line] via Oxford University</ref>

== Contributions to mathematics ==
[[File:Wallis - Opera mathematica, 1699 - 4760514 980122 3 00541.tif|thumb|''Opera mathematica'', 1699]]

Wallis made significant contributions to [[Trigonometry|trigonometry]], [[Calculus|calculus]], [[Geometry|geometry]], and the analysis of infinite series. In his ''Opera Mathematica'' I (1695) he introduced the term "[[Continued fraction|continued fraction]]".

===Analytic geometry===
In 1655, Wallis published a treatise on [[Conic section|conic section]]s in which they were defined analytically. This was the earliest book in which these curves are considered and defined as curves of the second [[Degree of a polynomial|degree]]. It helped to remove some of the perceived difficulty and obscurity of [[Biography:René Descartes|René Descartes]]' work on [[Analytic geometry|analytic geometry]].
In the ''Treatise on the Conic Sections'' Wallis popularised the symbol ∞ for infinity. He wrote, "I suppose any plane (following the ''Geometry of Indivisibles'' of Cavalieri) to be made up of an infinite number of parallel lines, or as I would prefer, of an infinite number of parallelograms of the same altitude; (let the altitude of each one of these be an infinitely small part 1/∞ of the whole altitude, and let the symbol ∞ denote Infinity) and the altitude of all to make up the altitude of the figure."<ref>Scott, J.F. 1981. ‘'The Mathematical Work of John Wallis, D.D., F.R.S. (1616–1703)’’. Chelsea Publishing Co. New York, NY. p. 18.</ref>

===Integral calculus===

''Arithmetica Infinitorum'', the most important of Wallis's works, was published in 1656. In this treatise the methods of analysis of Descartes and Cavalieri were systematised and extended, but some ideas were open to criticism. He began, after a short tract on conic sections, by developing the standard notation for powers, extending them from positive integers to [[Rational number|rational number]]s:

:<math>x^0 = 1</math>
:<math>x^{-1} = \frac{1}{x}</math>
:<math>x^{-n} = \frac{1}{x^n} \text{ etc.}</math>
:<math>x^{1/2} = \sqrt{x} </math>
:<math>x^{2/3} = \sqrt[3]{x^2} \text{ etc.}</math>
:<math>x^{1/n} = \sqrt[n]{x}</math>
:<math>x^{p/q} = \sqrt[q]{x^p}</math>

Leaving the numerous algebraic applications of this discovery, he next proceeded to find, by [[Integral|integration]], the [[Area|area]] enclosed between the curve ''y'' = ''x''<sup>''m''</sup>, ''x''-axis, and any ordinate ''x'' = ''h'', and he proved that the ratio of this area to that of the parallelogram on the same base and of the same height is 1/(''m''&nbsp;+&thinsp;1), extending [[Cavalieri's quadrature formula]]. He apparently assumed that the same result would be true also for the curve ''y'' = ''ax''<sup>''m''</sup>, where ''a'' is any constant, and ''m'' any number positive or negative, but he discussed only the case of the [[Parabola|parabola]] in which ''m'' = 2 and the [[Hyperbola|hyperbola]] in which ''m'' = −1. In the latter case, his interpretation of the result is incorrect. He then showed that similar results may be written down for any curve of the form

:<math>y = \sum_{m}^{} ax^{m}</math>

and hence that, if the ordinate ''y'' of a curve can be expanded in powers of ''x'', its area can be determined: thus he says that if the equation of the curve is ''y'' = ''x''<sup>0</sup> + ''x''<sup>1</sup> + ''x''<sup>2</sup> + ..., its area would be ''x'' + x<sup>2</sup>/2 + ''x''<sup>3</sup>/3 + ...&thinsp;. He then applied this to the [[Numerical integration|quadrature]] of the curves {{nowrap|1=''y'' = (''x'' − ''x''<sup>2</sup>)<sup>0</sup>}}, {{nowrap|1=''y'' = (''x'' − ''x''<sup>2</sup>)<sup>1</sup>}}, {{nowrap|1=''y'' = (''x'' − ''x''<sup>2</sup>)<sup>2</sup>}}, etc., taken between the limits ''x''&nbsp;=&nbsp;0 and ''x''&nbsp;=&nbsp;1. He shows that the areas are, respectively, 1, 1/6, 1/30, 1/140, etc. He next considered curves of the form {{nowrap|1=''y'' = ''x''<sup>1/''m''</sup>}} and established the theorem that the area bounded by this curve and the lines ''x''&nbsp;=&nbsp;0 and ''x''&nbsp;=&nbsp;1 is equal to the area of the rectangle on the same base and of the same altitude as ''m'' : ''m''&nbsp;+&thinsp;1. This is equivalent to computing

:<math>\int_0^1 x^{1/m}\,dx.</math>

He illustrated this by the parabola, in which case ''m'' = 2. He stated, but did not prove, the corresponding result for a curve of the form ''y'' = ''x''<sup>''p''/''q''</sup>.

Wallis showed considerable ingenuity in reducing the equations of curves to the forms given above, but, as he was unacquainted with the [[Binomial theorem|binomial theorem]], he could not effect the quadrature of the circle, whose equation is <math>y = \sqrt{1 - x^2}</math>, since he was unable to expand this in powers of ''x''. He laid down, however, the principle of [[Interpolation|interpolation]]. Thus, as the ordinate of the [[Circle|circle]] <math>y = \sqrt{1 - x^2}</math> is the [[Geometric mean|geometrical mean]] of the ordinates of the curves <math>y = (1 - x^2)^0</math> and <math>y = (1 - x^2)^1</math>, it might be supposed that, as an approximation, the area of the semicircle <math>\int_0^1 \!\sqrt{1 - x^2}\, dx</math> which is <math>\tfrac{1}{4}\pi</math> might be taken as the geometrical mean of the values of

:<math>\int_0^1 (1 - x^2)^0 \, dx \ \text{ and } \int_0^1 (1 - x^2)^1 \, dx,</math>

that is, <math>1</math> and <math>\tfrac{2}{3}</math>; this is equivalent to taking <math>4 \sqrt{\tfrac{2}{3}}</math> or 3.26... as the value of π. But, Wallis argued, we have in fact a series <math>1, \tfrac{1}{6}, \tfrac{1}{30}, \tfrac{1}{140},</math>... and therefore the term interpolated between <math>1</math> and <math>\tfrac{1}{6}</math> ought to be chosen so as to obey the law of this series.{{Clarify|date=July 2010}} This, by an elaborate method that is not described here in detail, leads to a value for the interpolated term which is equivalent to taking
:<math>\frac{\pi}{2} = \frac{2}{1}\cdot\frac{2}{3}\cdot\frac{4}{3}\cdot\frac{4}{5}\cdot\frac{6}{5}\cdot\frac{6}{7}\cdots</math>
(which is now known as the [[Wallis product]]).

In this work also the formation and properties of [[Continued fraction|continued fraction]]s are discussed, the subject having been brought into prominence by Brouncker's use of these fractions.

A few years later, in 1659, Wallis published a tract containing the solution of the problems on the [[Cycloid|cycloid]] which had been proposed by [[Biography:Blaise Pascal|Blaise Pascal]]. In this he incidentally explained how the principles laid down in his ''Arithmetica Infinitorum'' could be used for the rectification of algebraic curves and gave a solution of the problem to rectify (i.e., find the length of) the semicubical parabola ''x''<sup>3</sup> = ''ay''<sup>2</sup>, which had been discovered in 1657 by his pupil William Neile. Since all attempts to rectify the [[Ellipse|ellipse]] and hyperbola had been (necessarily) ineffectual, it had been supposed that no curves could be rectified, as indeed Descartes had definitely asserted to be the case. The [[Logarithmic spiral|logarithmic spiral]] had been rectified by [[Biography:Evangelista Torricelli|Evangelista Torricelli]] and was the first curved line (other than the circle) whose length was determined, but the extension by Neile and Wallis to an algebraic curve was novel. The cycloid was the next curve rectified; this was done by Christopher Wren in 1658.

Early in 1658 a similar discovery, independent of that of Neile, was made by van Heuraët, and this was published by van Schooten in his edition of Descartes's ''Geometria'' in 1659. Van Heuraët's method is as follows. He supposes the curve to be referred to rectangular axes; if this is so, and if (''x'', ''y'') are the coordinates of any point on it, and ''n'' is the length of the normal,{{Clarify|date=July 2010}} and if another point whose coordinates are (''x'', ''η'') is taken such that ''η'' : ''h'' = ''n'' : ''y'', where ''h'' is a constant; then, if ''ds'' is the element of the length of the required curve, we have by similar triangles ''ds'' : ''dx'' = ''n'' : ''y''. Therefore, ''h ds'' = ''η'' ''dx''. Hence, if the area of the [[Locus (mathematics)|locus]] of the point (''x'', ''η'') can be found, the first curve can be rectified. In this way van Heuraët effected the rectification of the curve ''y''<sup>3</sup> = ''ax''<sup>2</sup> but added that the rectification of the parabola ''y''<sup>2</sup> = ''ax'' is impossible since it requires the quadrature of the hyperbola. The solutions given by Neile and Wallis are somewhat similar to that given by van Heuraët, though no general rule is enunciated, and the analysis is clumsy. A third method was suggested by [[Biography:Pierre de Fermat|Fermat]] in 1660, but it is inelegant and laborious.

===Collision of bodies===

The theory of the collision of bodies was propounded by the Royal Society in 1668 for the consideration of mathematicians. Wallis, Christopher Wren, and [[Biography:Christiaan Huygens|Christiaan Huygens]] sent correct and similar solutions, all depending on what is now called the [[Physics:Conservation of momentum|conservation of momentum]]; but, while Wren and Huygens confined their theory to perfectly elastic bodies ([[Physics:Elastic collision|elastic collision]]), Wallis considered also imperfectly elastic bodies ([[Physics:Inelastic collision|inelastic collision]]). This was followed in 1669 by a work on [[Physics:Statics|statics]] (centres of gravity), and in 1670 by one on [[Physics:Analytical dynamics|dynamics]]: these provide a convenient synopsis of what was then known on the subject.

===Algebra===

In 1685 Wallis published ''Algebra'', preceded by a historical account of the development of the subject, which contains a great deal of valuable information. The second edition, issued in 1693 and forming the second volume of his ''Opera'', was considerably enlarged. This algebra is noteworthy as containing the first systematic use of formulae. A given magnitude is here represented by the numerical ratio which it bears to the unit of the same kind of magnitude: thus, when Wallis wants to compare two lengths he regards each as containing so many units of length. This perhaps will be made clearer by noting that the relation between the space described in any time by a particle moving with a uniform velocity is denoted by Wallis by the formula

:''s'' = ''vt'',

where ''s'' is the number representing the ratio of the space described to the unit of length; while the previous writers would have denoted the same relation by stating what is equivalent to the proposition

:''s''<sub>1</sub> : ''s''<sub>2</sub> = ''v''<sub>1</sub>''t''<sub>1</sub> : ''v''<sub>2</sub>''t''<sub>2</sub>.

===Number line===
[[File:Wallis2.png|thumb|325px|Referring to advancing and retreating from point <math>A</math>, Wallis wrote in ''A treatise of algebra'' that "...<math>-3</math> doth as truly design the Point <math>D</math>; as <math>+3</math> designed the Point <math>C</math>{{nbsp}}... And each designs (at least in the same Infinite Line) one Single Point: And but one."]]

Wallis has been credited as the originator of the [[Number line|number line]] "for negative quantities"<ref name="Heeffer2011">{{cite journal | last1 = Heeffer | first1 = Albrecht | date = 10 March 2011 | title = Historical Objections Against the Number Line | url = https://link.springer.com/article/10.1007/s11191-011-9349-0 | journal = Science & Education | volume = 20 | issue = 9 | pages = 863–880 [872–876] | doi = 10.1007/s11191-011-9349-0| bibcode = 2011Sc&Ed..20..863H | hdl = 1854/LU-1891046 | s2cid = 120058064 }}</ref> and "for operational purposes."<ref>{{cite conference |url = https://cogsci.ucsd.edu/~nunez/web/Nunez_ch3_MN.pdf | title = How Much Mathematics Is "Hardwired," If Any at All: Biological Evolution, Development, and the Essential Role of Culture | last1 = Núñez | first1 = Rafael | editor1-last = Sera | editor1-first = Maria D.| editor2-last = Carlson | editor2-first = Stephanie M. | editor3-last = Maratsos | editor3-first = Michael |  date = 2017 | publisher =  John Wiley & Sons, Inc. | book-title = Minnesota Symposium on Child Psychology: Culture and Developmental Systems, Volume 38 | pages = 83–124 [96] | doi = 10.1002/9781119301981.ch3}}</ref> This is based on a passage in his 1685 treatise on algebra in which he introduced a number line to illustrate the legitimacy of negative quantities:<ref name="A treatise of algebra">{{cite book |last=Wallis |first=John |date=1685 |title=A treatise of algebra, both historical and practical |url=https://echo.mpiwg-berlin.mpg.de/ECHOdocuView?url=%2Fpermanent%2Flibrary%2FH3GRV5AU%2Fpageimg&start=251&viewMode=image&mode=imagepath&pn=292 |location=London |publisher=Richard Davis |page=265 |id=[https://echo.mpiwg-berlin.mpg.de/ECHOdocuView?mode=imagepath&url=/permanent/library/H3GRV5AU/pageimg MPIWG:GK8U243K]}}</ref>

<blockquote>Yet is not that Supposition (of Negative Quantities) either Unuseful or Absurd; when rightly understood. And though, as to the bare Algebraick Notation, it import a Quantity less than nothing: Yet, when it comes to a Physical Application, it denotes as Real a Quantity as if the Sign were <math>+</math>; but to be interpreted in a contrary sense... <math>+3</math>, signifies <math>3</math> Yards Forward; and <math>-3</math>, signifies <math>3</math> Yards Backward.</blockquote>

It has also been noted that, in an earlier work, Wallis came to the conclusion that the ratio of a positive number to a negative one is greater than infinity. The argument involves the quotient <math>\tfrac{1}{x}</math> and considering what happens as <math>x</math> approaches and then crosses the point <math>x = 0</math> from the positive side.<ref name="Martínez2006">{{cite book|author=Martínez, Alberto A.|title=Negative Math: How Mathematical Rules Can Be Positively Bent|url=https://books.google.com/books?id=8HSodlYby9MC&pg=PA22|access-date=9 June 2013|year=2006|publisher=Princeton University Press|isbn=978-0-691-12309-7|page=22}}</ref> Wallis was not alone in this thinking: [[Biography:Leonhard Euler|Leonhard Euler]] came to the same conclusion by considering the geometric series <math>\tfrac{1}{1-x} = 1 + x + x^2 + \cdots</math>, evaluated at <math>x=2</math>, followed by reasoning similar to Wallis's (he resolved the paradox by distinguishing different kinds of negative numbers).<ref name="Heeffer2011" />

===Geometry===
He is usually credited with the proof of the [[Pythagorean theorem]] using similar triangles. However, Thabit Ibn Qurra (AD 901), an Arab mathematician, had produced a generalisation of the Pythagorean theorem applicable to all triangles six centuries earlier. It is a reasonable conjecture that Wallis was aware of Thabit's work.<ref>{{cite book|first=G.G.|last=Joseph|title=The Crest of the Peacock: Non-European Roots of Mathematics|edition=2|publisher=Penguin|year=2000|isbn=978-0-14-027778-4|page=337}}</ref>

Wallis was also inspired by the works of Islamic mathematician Sadr al-Tusi, the son of [[Biography:Nasir al-Din al-Tusi|Nasir al-Din al-Tusi]], particularly by al-Tusi's book written in 1298 on the [[Parallel postulate|parallel postulate]]. The book was based on his father's thoughts and presented one of the earliest arguments for a non-Euclidean hypothesis equivalent to the parallel postulate. After reading this, Wallis then wrote about his ideas as he developed his own thoughts about the postulate, trying to prove it also with similar triangles.<ref>The Mathematics of Egypt, Mesopotamia, China, India, and Islam:A Sourcebook [http://press.princeton.edu/chapters/i8583.html Victor J. Katz Princeton University Press]</ref>

He found that [[Parallel postulate|Euclid's fifth postulate]] is equivalent to the one currently named  "Wallis postulate" after him. This postulate states that "On a given finite straight line it is always possible to construct a triangle similar to a given triangle". This result was encompassed in a trend trying to deduce Euclid's fifth from the other four postulates which today is known to be impossible. Unlike other authors, he realised that the unbounded growth of a triangle was not guaranteed by the four first postulates.<ref>{{citation|first=David M.|last=Burton|title=The History of Mathematics / An Introduction|edition=7th|year=2011|publisher=McGraw-Hill|isbn=978-0-07-338315-6|page=566}}</ref>

===Calculator===

Another aspect of Wallis's mathematical skills was his ability to do mental calculations. He slept badly and often did mental calculations as he lay awake in his bed. One night he calculated in his head the square root of a number with 53 digits. In the morning he dictated the 27-digit square root of the number, still entirely from memory. It was a feat that was considered remarkable, and Henry Oldenburg, the Secretary of the Royal Society, sent a colleague to investigate how Wallis did it. It was considered important enough to merit discussion in the ''Philosophical Transactions'' of the Royal Society of 1685.<ref>Dr. Wallis (1685) "Two extracts of the Journal of the Phil. Soc. of Oxford; one containing a paper, communicated March 31, 1685, by the Reverend Dr. Wallis, president of that society, concerning the strength of memory when applied with due attention; … ", ''Philosophical Transactions of the Royal Society of London'', '''15''' :  1269-1271.  Available on-line at: 
[http://rstl.royalsocietypublishing.org/content/15/167-178/1269.full.pdf+html Royal Society of London]{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{citation|title=The Common Scientist of the Seventeenth Century: A Study of the Dublin Philosophical Society, 1683–1708|volume=15|series=Routledge Library Editions: History & Philosophy of Science|first=K. Theodore|last=Hoppen|publisher=Routledge|year=2013|isbn=9781135028541|url=https://books.google.com/books?id=PHK7ErKBiCEC&pg=PA157|page=157}}</ref>

== Musical theory ==
Wallis translated into Latin works of [[Biography:Ptolemy|Ptolemy]] and Bryennius, and Porphyrius's commentary on Ptolemy.  He also published three letters to Henry Oldenburg concerning tuning. He approved of equal temperament, which was being used in England's organs.<ref>David Damschoder and David Russell Williams, ''Music Theory from Zarlino to Schenker: A Bibliography and Guide'' (Stytvesant, NY: Pendragon Press, 1990), p. 374.</ref>

==Other works==
[[File:Wallis - Opera mathematica, 1657 - 4611280.tif|thumb|''Opera mathematica'', 1657]]His ''Institutio logicae'', published in 1687, was very popular.<ref name="EB1911">{{Cite EB1911 |wstitle=Wallis, John |volume=28 |page=284–285}}</ref> The ''Grammatica linguae Anglicanae'' was a work on English grammar, that remained in print well into the eighteenth century. He also published on theology.<ref name=EB1911/>

== See also ==
* [[Astronomy:31982 Johnwallis|31982 Johnwallis]], an asteroid that was named after him
* Invisible College
* John Wallis Academy – former ChristChurch school in Ashford renamed in 2010
* [[Wallis's conical edge]]
* [[Wallis' integrals]]

==Footnotes==
{{Reflist}}

== References ==
* The initial text of this article was taken from the [[Social:Public domain|public domain]] resource:
* [[Biography:W. W. Rouse Ball|W. W. Rouse Ball]] (1908) ''[http://www.maths.tcd.ie/pub/HistMath/People/Wallis/RouseBall/RB_Wallis.html A Short Account of the History of Mathematics],'' 4th ed.
* {{cite journal | last1 = Scriba | first1 = C J |  year = 1970 | title = The autobiography of John Wallis, F.R.S. | journal = Notes and Records of the Royal Society of London | volume = 25 | pages = 17–46 | doi=10.1098/rsnr.1970.0003| s2cid = 145393357 }}
* Stedall, Jacqueline, 2005, "Arithmetica Infinitorum" in [[Biography:Ivor Grattan-Guinness|Ivor Grattan-Guinness]], ed., ''Landmark Writings in Western Mathematics''. Elsevier: 23–32.
* Guicciardini, Niccolò (2012) "John Wallis as editor of Newton's Mathematical Work", ''Notes and Records of the Royal Society of London'' 66(1): 3–17. [https://www.jstor.org/stable/41723282 Jstor link]
* Stedall, Jacqueline A. (2001) "Of Our Own Nation: John Wallis's Account of Mathematical Learning in Medieval England", Historia Mathematica 28: 73.
* Wallis, J. (1691). A seventh letter, concerning the sacred Trinity occasioned by a second letter from W.J. / by John Wallis ... (Early English books online). London: Printed for Tho. Parkhurst ...

==External links==
* [http://emlo.bodleian.ox.ac.uk/forms/advanced?col_cat=Wallis%2C+John The Correspondence] of [http://emlo.bodleian.ox.ac.uk/blog/?catalogue=john-wallis John Wallis]  in [http://emlo.bodleian.ox.ac.uk/home EMLO]
* {{DNB Cite|wstitle=Wallis, John (1616-1703)}}
* {{MacTutor Biography|id=Wallis}}
* [http://galileo.rice.edu/Catalog/NewFiles/wallis.html Galileo Project page]
* {{UK National Archives ID}}
* {{NPG name}}
* [http://lhldigital.lindahall.org/cdm/ref/collection/math/id/11231 John Wallis (1685) ''A treatise of algebra''] - digital facsimile, Linda Hall Library
* {{cite book |first=John |last=Wallis |title=A Treatise of Algebra, both Historical and Practical. Shewing the Original, Progress, and Advancement thereof, from time to time, and by what Steps it hath attained to the Heighth at which it now is |publisher=Richard Davis |location=Oxford |date=1685 |url=http://www.e-rara.ch/zut/content/titleinfo/2507537 |doi=10.3931/e-rara-8842}}
* {{cite book |last1=Hutchinson |first1=John |title=Men of Kent and Kentishmen |date=1892 |publisher=Cross & Jackman |location=Canterbury |pages=139–140 |edition=Subscription  |chapter=John Wallis}}

{{Savilian Professors of Geometry}}


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[[Category:Historians of mathematics]]
[[Category:Calculus]]
[[Category:Infinity]]
[[Category:History of mathematics]]
[[Category:Mathematics of infinitesimals]]

{{Sourceattribution|John Wallis|1}}