Gustav Theodor Fechner (; German: ['f?çn?]; 19 April 1801 – 18 November 1887) was a German philosopher, physicist and experimental psychologist.
An early pioneer in experimental psychology and founder of psychophysics, he inspired many 20th-century scientists and philosophers.
He is also credited with demonstrating the non-linear relationship between psychological sensation and the physical intensity of a stimulus via the formula:
S
=
K
ln
?
I
{\displaystyle S=K\ln I}
, which became known as the Weber–Fechner law.