Bernoulli, Daniel (1700–1782)

Swiss mathematical physicist. He made important contributions to trigonometry and differential equations (differentiation). In hydrodynamics he proposed Bernoulli's principle, an early formulation of the idea of conservation of energy.

Bernoulli was born in Groningen in the Netherlands, the son of mathematician Johann Bernoulli. Having studied philosophy, logic, and medicine in Basel, Switzerland, he became professor of mathematics at the St Petersburg Academy, Russia, 1725–32, and professor of anatomy and botany at the University of Basel from 1733. During his career he won ten prizes from the French Academy, for papers on subjects that included marine technology, oceanology, astronomy, and magnetism.

Bernoulli's Hydrodynamica (1738) is both a theoretical and practical study of equilibrium, pressure, and velocity in fluids. Bernoulli's principle states that the pressure of a moving fluid decreases the faster it flows (which explains the origin of lift on the aerofoil of an aircraft's wing). Hydrodynamica also contains the first attempt at a thorough mathematical explanation of the behaviour of gases by assuming they are composed of tiny particles, producing an equation of state that enabled Bernoulli to relate atmospheric pressure to altitude, for example. This was the first step towards the kinetic theory of gases achieved a century later.

Among his achievements in mathematics, Bernoulli demonstrated how the differential calculus could be used in problems of probability. He did pioneering work in trigonometrical series and the computation of trigonometrical functions. Bernoulli also showed the shape of the curve known as the lemniscate.