Mature Work
In 1795 Playfair published an alternative, more stringent formulation of Euclid's parallel postulate, which is now called Playfair'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.
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 controversy that arose in connexion with Sir John Leslie's appointment to the post he had vacated, and published a satirical Letter (1806).
Playfair was an opponent of Gottfried Leibniz's vis viva principle, an early version of the conservation of energy. In 1808, he launched an attack on John Smeaton and William Hyde Wollaston's work championing the theory.
Although a wealthy man, Playfair was buried in an unmarked grave in Old Calton Cemetery, on Waterloo Place in Edinburgh. However, the monument to his memory, on Calton Hill, is visible from the spot.
Read more about this topic: John Playfair
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