- John Playfair
Professor **John Playfair**FRSE (March 10 ,1748 –July 20 ,1819 ) was a Scottishscientist .Playfair was professor of

mathematics and later professor ofnatural philosophy at theUniversity of Edinburgh . He is perhaps best known for his book "Illustrations of the Huttonian Theory of the Earth " (1802), which was a summary of the work ofJames Hutton . It was through this that Hutton's principle of uniformitarianism, later taken up byCharles Lyell , first reached a wide audience.In 1795 Playfair published an alternative, more stringent formulation of

Euclid 's parallel postulate calledPlayfair's axiom ; though the axiom bears Playfair's name, he did not create it, but credited others, in particular William Ludlam, with the prior use of it. [*J. Playfair and Euclid, Elements of Geometry: Containing the First Six Books of Euclid : with a. J.B. Lippincott & Co, 1860, p. 291. Available online from Google Books.*]**Early life**Born at

Benvie ,Angus , Scotland, where his father wasparish minister, he was educated at home until the age of fourteen, when he entered theUniversity of St Andrews . In 1766, when only eighteen, he was candidate for the chair of mathematics inMarischal College ,University of Aberdeen , and, although he was unsuccessful, his claims were admitted to be high.Six years later he made application for the chair of natural philosophy in his own university, but again without success, and in 1773 he was offered and accepted the

benefice of the unitedparish es of Liff and Benvie, vacant by the death of his father. He continued, however, to carry on his mathematical and physical studies, and in 1782 he resigned his charge in order to become the tutor ofFerguson of Raith . By this arrangement he was able to be frequently inEdinburgh and to cultivate the literary and scientific society for which it was at that time specially distinguished. In particular, he attended the natural history course of John Walker. ThroughNevil Maskelyne , whose acquaintance he had first made in the course of the celebratedSchiehallion experiments in 1774, he also gained access to the scientific circles ofLondon . In 1785 whenDugald Stewart succeeded Ferguson in the Edinburgh chair ofmoral philosophy , Playfair succeeded the former in that of mathematics.**Mature work**In 1802, he published his celebrated volume entitled "Illustrations of the Huttonian Theory of the Earth." The influence exerted by

James Hutton on the development ofgeology is thought to be largely due to its publication. In 1805 he exchanged the chair of mathematics for that of natural philosophy in succession to John Robison, whom also he succeeded asgeneral secretary to theRoyal Society of Edinburgh . He took a prominent part, on the liberal side, in theecclesiastical controversy that arose in connexion with Sir John Leslie's appointment to the post he had vacated, and published asatirical Letter (1806).Playfair was an opponent of

Gottfried Leibniz 's "vis viva " principle, an early version of theconservation of energy . In 1808, he launched an attack [*"Edinburgh Review",*] on**12**, 1808, 120–130John Smeaton andWilliam Hyde Wollaston 's work championing the theory.**Family**John's brothers were architect

James Playfair and engineerWilliam Playfair . [*"Biographical Dictionary of Eminent Scotsmen" (1856), reproduced in " [*]*http://www.electricscotland.com/history/other/playfair_john.htm Significant Scots*] "**Honours***

Fellow of the Royal Society of Edinburgh

*Fellow of the Royal Society of London, 1807

*Craters on Mars and theMoon were named in his honor.**Critical bibliography**A collected edition of Playfair's works, with a memoir by James G. Playfair, appeared at Edinburgh in 4 vols. 8vo.

His writings include a number of essays contributed to the "

Edinburgh Review " from 1804 onwards, various papers in the Phil. Trans. (including his earliest publication, " On the Arithmetic of Impossible Quantities," 1779, and an " Account of the Lithological Survey of Schehallion," 1811) and in the "Transactions of the Royal Society of Edinburgh " (" On the Causes which affect the Accuracy of Barometrical Measurements," &c.), also the articles "Aepinus" and "Physical Astronomy," and a "Dissertation on the Progress of Mathematical and Physical Science since the Revival of Learning in Europe," in theEncyclopædia Britannica (Supplement to fourth, fifth and sixth editions).His "

Elements of Geometry " first appeared in 1795 and have passed through many editions; his "Outlines of Natural Philosophy " (2 vols., 1812-1816) consist of the propositions andformulae which were the basis of his class lectures. Playfair's contributions topure mathematics were not considerable, his paper "On the Arithmetic of Impossible Quantities," that " On the Causes which affect the Accuracy of Barometrical Measurements," and his "Elements of Geometry ", all already referred to, being the most important. His lives ofMatthew Stewart , Hutton,Robison , many of hisreview s, and above all his "Dissertation " are of the utmost value.**Notes****External links*** [

*http://www.chlt.org/sandbox/lhl/dsb/page.34.php?size=240x320 Dictionary of Scientific Biography*]

*

* [*http://www.electricscotland.com/history/other/playfair_john.htm Significant Scots: John Playfair*]

* [*http://www.npg.org.uk/live/search/person.asp?search=ss&sText=playfair&LinkID=mp03581 National Portrait Gallery*]**References***1911

*Wikimedia Foundation.
2010.*