Fechner's Law

That the increase of the stimulus nece ary to produce an increase of the sensation bears a constant ratio to the total stimulus; more exactly, that in order that the intensity of a sensation may increase in arithmetical progre ion, the stimulus must increase in a geometrical progre ion; or, as formulated by Fechner, the sensation increases as the logarithm of the stimulus. The principle is true only within certain limits, and does not hold with equal exactne for all the senses, its operation being more positive in the middle regions of sensibility, and in the fields of sight, hearing, pre ure, and muscular sense, and becoming very uncertain as one approaches the upper and lower limits of sensibility. The interpretation of the law has given rise to much difference of opinion. Fechner regarded it as the fundamental formula of. the relation between body and mind, but in this he has not been generally followed. The question whether it be a statement of psychological, physiological, or psycho-physiological relation has not yet been solved, the trend of opinion at the present day, however, being toward a physiological explanation.