Gustav Theodore Fechner
A student of Weber, Gustav Theodore Fechner wrote Weber’s idea in the form of a formula, and called it Weber’s Law. He revised Weber’s law (showing it was logarithmic), and continued Weber’s work on jnd (just noticeable difference), applying it to weight, temperature, etc.
Fechner’s accomplishments are not limited to expanding on Weber’s insights. He studied afterimages and color vision. His description of the “pleasure principle ” influenced Freud years later.
And he solved one of life “insoluble” questions. Although philosophers had struggled to determine how the mind and body interrelate, Fechner proposed an elegant solution to the problem. On October 22, 1850, Fechner had a sudden burst of insight. He saw a quantitative relationship between stimulus (the mind) and sensation (the body). Sensation is dependent on stimulation but they increase at different rates. An increase in sensation requires a geometrical increase in stimulation.