# Stokes, George Gabriel (1819–1903)

George Stokes was a British mathematician and physicist, born in Ireland. He was professor of mathematics (1849–1903) at Cambridge and served as president (1885–92) of the Royal Society.

Stokes is celebrated for his law of viscosity (see below), which describes the movement of a solid sphere in a fluid. It forms the basis of the modern theory of viscous fluids.

He also developed
an important theorem of vector analysis,
accurately described and named fluorescence,
and proposed the concept of an ether. Stokes'
book, *Dynamic Theory of Diffraction* (1849) was an important work
in the wave theory of light. He was a pioneer of geodesy.

## Stokes' law

Stokes' law is a formula that gives the terminal
velocity at which particles fall in a fluid (liquid or gas). For particles of radius *r* (less than 0.1millimeter) the
terminal velocity is 2(*d*_{1} - *d*_{2})*gr*^{ 2}/9ρ, where *d*_{1} and *d*_{2} are the densities of the particle and the fluid, *g* is the acceleration
due to gravity, and ρ is the viscosity of the fluid. Stokes'
forms the basis of the modern theory of viscous fluids.