Fechner, Gustav Theodor, 1801-87, German philosopher and physicist, founder of psychophysics, educated at Dresden and Leipzig. He became professor of physics at Leipzig in 1834 but was forced by ill health to leave in 1839. Thereafter he devoted himself largely to the study of the relationship between body and mind, although under the name "Dr. Mises" he also wrote humorous satire. In philosophy he was an animist, maintaining that life is manifest in all objects of the universe. His greatest achievement was in the investigation of exact relationships in psychology and aesthetics. He formulated the rule known as Fechner's, or Weber's, law, that, within limits, the intensity of a sensation increases as the logarithm of the stimulus. Two of Fechner's most important works were Zendavesta (1851) and Elementen der Psychophysik (1860).