Gustav Theodor Fechner (19 April 1801 – 18 November 1887) was a German physicist, philosopher, and experimental psychologist. As a pioneer of experimental psychology (Eng) and founder of psychophysics (techniques for measuring the mind), he inspired many scientists and philosophers in the 20th century. He is also credited with demonstrating the nonlinear relationship between psychological sensation and the physical intensity of a stimulus using the formula: S = K ln I {\displaystyle S=K\ln I}, which became known as the Weber–Fechner law.