Gustav Fechner

Gustav Theodor Fechner was a German physicist, philosopher, and experimental psychologist born 19 April 1801. He founded psychophysics, inventing techniques to measure the mind with the precision of physical science. His central breakthrough came in demonstrating the non-linear relationship between psychological sensation and stimulus intensity, captured in the formula S = K ln I — later called the Weber–Fechner law. The work made him a pioneer in experimental psychology and seeded ideas that shaped scientists and philosophers through the 20th century. He died 18 November 1887.