John Playfair

John Playfair FRSE, FRS (10 March 1748 – 20 July 1819) was a Church of Scotland minister, remembered as a scientist and mathematician, and a professor of natural philosophy at the University of Edinburgh. He is best known for his book ''Illustrations of the Huttonian Theory of the Earth'' (1802), which summarised the work of James Hutton. It was through this book that Hutton's principle of uniformitarianism, later taken up by Charles Lyell, first reached a wide audience. Playfair's textbook ''Elements of Geometry'' made a brief expression of Euclid's parallel postulate known now as Playfair's axiom.

In 1783 he was a co-founder of the Royal Society of Edinburgh. He served as General Secretary to the society 1798–1819.

Life

Born at Benvie, slightly west of Dundee to Margaret Young (1719/20 – 1805) and Reverend James Playfair (died 1772), the kirk minister of Liff and Benvie.

Playfair was educated at home until the age of 14, when he entered the University of St Andrews to study divinity. He also did further studies at Edinburgh University. In 1766, when only 18, he was a candidate for the chair of mathematics in Marischal College (now part of the University of Aberdeen), and, although he was unsuccessful, his claims were admitted to be high.

Six years later (1772) he applied for the chair of natural philosophy (physics) at St Andrews University, but again without success. In 1773 he was licensed to preach by the Church of Scotland and was offered the united parishes of Liff and his home parish of Benvie (made vacant by the death of his father). However, Playfair chose to continue his studies in mathematics and physics, and in 1782 he resigned his charge to become the tutor of Adam Ferguson. By this arrangement Playfair regularly visited Edinburgh and went on to cultivate the literary and scientific society for which the city was at that time specially distinguished. In particular, he attended the natural history course of John Walker. Through Nevil Maskelyne, whose acquaintance he had first made in the course of the celebrated Schiehallion experiments in 1774, he also gained access to the scientific circles of London. In 1785 when Dugald Stewart succeeded Ferguson in the University of Edinburgh Chair of Moral Philosophy, Playfair succeeded the former to become the chair of mathematics.

In 1795 Playfair published an alternative, more stringent formulation of Euclid's parallel postulate, which is now called Playfair's axiom. Although the axiom bears Playfair's name, he did not create it, but credited others, in particular William Ludlam with its prior use.

In 1802 Playfair published his celebrated volume entitled ''Illustrations of the Huttonian Theory of the Earth.'' The influence exerted by James Hutton on the development of geology is thought to be largely due to its publication. In 1805 Playfair exchanged the Chair of Mathematics for that of natural philosophy in succession to John Robison, whom also he succeeded as general secretary to the Royal Society of Edinburgh. He took a prominent part, on the liberal side, in the ecclesiastical