# Sir Isaac Newton

**Newton, Sir Isaac** (1642–1727), English natural philosopher and mathematician, the discoverer of the calculus and author of the theory of universal gravitation. Professor of mathematics at Cambridge University (1669–1701), he wrote *Mathematical Principles of Natural Philosophy (Principia;* 1687), covering dynamics, fluid mechanics, and tides. His theory of light was developed in *Optics* (1704). He built the first reflecting telescope (1668). He is best known for his work in gravitation.

*See also:* Calculus; Gravitation.

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