Professor John Playfair, geologist, physicist and mathematician, died on the 20th of July, 1819.
John Playfair was a Professor of Natural Philosophy at the University of Edinburgh, who is perhaps best known for his book ‘Illustrations of the Huttonian Theory of the Earth’, which clarified the revolutionary ideas of his close friend, the geologist, James Hutton. It was through that book that Hutton's principle of ‘uniformitarianism’ first reached a wide audience. Playfair is also well known for his work in ‘geomorphology’, which is that large rock could be transported as part of the process of glaciation and that rivers carve out their own valleys. However, he was a mathematician first and foremost and should not be forgotten for his contributions to that discipline, where he is remembered by ‘Playfair's Axiom’; his alternative to Euclid’s ‘parallel’ postulate.
John Playfair was a contributor to the ‘Scottish Enlightenment’ and was a colleague, contemporary and peer of some very famous names. That roll call included such great scholars as Dugald Stewart the mathematician, Adam Smith the economist, Joseph Black the chemist, James Hutton the geologist, Robert Adam the architect and engineer, and Principal Robinson the historian. How wonderful that all these great men knew each other and met over a few drinks to discuss their ideas. Late 18th Century Edinburgh must have been a very interesting place to be and it’s surely not surprising that its legacy attracts many cultural tourists in the 21st Century.
John Playfair was born at Benvie, near Dundee, on the 10th of March, 1748. He came from a very talented family as one of his brothers was the architect, James Playfair, whilst another was the engineer and inventor of statistical graphics, William Playfair. John Playfair’s nephew was the architect William Henry Playfair; the man who designed the Edinburgh of the 1800s and was later, in 1825, responsible for the majestic public memorial to his uncle, the Playfair Monument on Calton Hill by the New Observatory.
Playfair was educated by his father at home until the age of fourteen, when he was sent to the University of St Andrews to study for a general degree with the aim of entering the Church. Playfair was awarded a scholarship and his aptitude and keenness gained him the respect and friendship of his Professors. His progress in the mathematical sciences was so rapid that Wilkie, the Professor of Natural Philosophy and the author of the ‘Epigoniad’, chose Playfair the student to deputise for him when he was ill. John graduated from St Andrews, in 1765, with an M.A. and a year later, when still only eighteen, he applied for the position of Professor of Mathematics at Aberdeen’s Marischal College. Narrowly failing to get the job, he applied again, in 1772, for the post of Professor of Natural Philosophy at the University of St Andrews, but neither did he get that job. Nevertheless, he had clearly demonstrated his extraordinary talent and knowledge of mathematics.
In the meantime, Playfair studied Divinity at St Mary's College, St Andrews. In 1769, he left the University and spent much of his time in Edinburgh until, in 1772, his father died. That meant Playfair had to assume responsibility for the care of his mother and younger brothers. So he took over as Minister of his father’s Parishes of Liff and Benvie, in August, 1773. However, he still found time to continue with his philosophical studies and mixed with the luminaries of the Scottish Enlightenment.
In 1774, Playfair became friends with Neville Maskelyne, the Astronomer Royal, who persuaded him to submit his first paper on mathematics to the Royal Society of London. ‘On the Arithmetic of Impossible Quantities’ was successfully published in the ‘Philosophical Transactions’, in 1779. He went on to publish on various topics in the ‘Transactions of the Royal Society of Edinburgh’ and also contributed to the ‘Edinburgh Review’ and the ‘Encyclopaedia Britannica’.
Playfair became Moderator of the Synod of the Church of Scotland, but in 1782, he resigned his church position to become tutor to the sons of Ferguson of Raith, whom he tutored through to 1787. Then, in 1785, Playfair returned to his true vocation, when he was offered the Chair of Mathematics at the University of Edinburgh. Later, in 1805, he moved to the Chair of Natural Philosophy (a post which he held until his death) and in the same year he became General Secretary of the Royal Society of Edinburgh.
In 1795, Playfair published an edition of ‘Euclid’s Elements’, containing the innovation of using algebraic notation to abbreviate the proofs, which he taught in his class. He also dealt with one problem inherent in the ‘Elements’. Playfair worked on Euclid’s contentious fifth or ‘parallel’ postulate. In my mind, the contentiousness comes from the use of ‘parallel’, but in fact the problem lay with the implied (or the assumption of) parallelism. Playfair introduced what became known as ‘Playfair’s Axiom’, which proves the point (sic). To be fair, he stated quite clearly that he had derived it from Proclus, but it’s stuck with his name.
The death of his friend, James Hutton, in 1797, caused Playfair to begin a biographical memoir, but that turned into a response to Hutton’s critics, which appeared, in 1802, as the ‘Illustrations of the Huttonian Theory of the Earth’. Playfair’s genius was to present Hutton's theories in a more intelligible, accessible style than the original presentation. Playfair's simple and eloquent method produced a series of chapters clearly stating the Huttonian theory, giving the facts to support it and refuting the arguments against. The success of his book can be seen in that Hutton is now regarded as the father of the modern science of geology. His biographical sketch of Hutton was published in the ‘Transactions of the Royal Society of Edinburgh’, in 1803.
The Astronomical Institution of Edinburgh was founded in 1811, nine years before the Royal Astronomical Society in England. Playfair was its first president and he was instrumental in getting the New Observatory on Calton Hill built. Playfair also published two volumes on natural philosophy, covering dynamics, mechanics, hydrostatics, hydraulics, aerostatics, pneumatics and astronomy. A third volume intended to cover optics, electricity, and magnetism, was unfortunately never completed.
After the defeat of Napoleon, in 1815, the sixty-eight years old Playfair went to the Continent to gather material for the second edition of the ‘Illustrations’. He embarked on an arduous journey through France, Switzerland and Italy to examine the geological structure of those parts of the world and intended a fundamental assertion of the principles of geology. Sadly, the second edition never saw the light of day as Playfair succumbed to an illness of the bladder. After a month long illness Playfair died at Burntisland in Fife on the 20th of July, 1819. He was buried in the Old Calton Burial Ground, adjacent to David Hume, overlooked by the Observatory that he helped create and the memorial erected by his nephew.