Euler, Leonhard (1707-1783)

Swiss mathematician. He developed the theory of differential equations and the calculus of variations, and worked in astronomy and optics. He also enlarged mathematical notation. Euler developed spherical trigonometry and demonstrated the significance of the coefficients of trigonometric expansions; Euler's number (e, as it is now called) has various useful theoretical properties and is used in the summation of particular series. Euler was born and educated in Basel, a pupil of Johann Bernoulli. He became professor of physics at the University of St Petersburg 1730. In 1741 he was invited to Berlin by Frederick the Great, where he spent 25 years before returning to Russia. Euler carried out research into the motion and positions of the Moon, and the gravitational relationships between the Moon, the Sun, and the Earth. His resulting work on tidal fluctuations took him into the realm of fluid mechanics.