FECHNER'S LAW, in psychology, states that the inten sity of a sensation (1) varies with the logarithm of the strength of the stimulus (S), or briefly I=C log. S, when C is a constant which is different for different sensations (seeing, hearing, etc.), or even for the same kind of sensation in the case of different individuals. This law is sometimes combined with Weber's Law (q.v.), from which it is derived, and called the Weber-Fechner Law. (See PSYCHOLOGY.)