Playfair, John, 1748–1819, Scottish mathematician, physicist, and geologist. He was educated at St. Andrews and Edinburgh and taught first mathematics and then physics and astronomy at the latter university. His Illustrations of the Huttonian Theory of the Earth (1802) elucidated the methods and principles of his friend James Hutton and established uniformitarianism as the foundation of the new science of geology. He also published texts on geometry, physics, and astronomy.
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