Ernst Heinrich Weber made important discoveries about the sense of touch and invented the idea of the just-noticeable difference between two similar physical stimuli. He founded psychophysics, the branch of psychology that studies the relations between physical stimuli and mental states.

Weber, the third of 13 children, was born June 24, 1795, in Wittenburg, Germany. His father was Michael Weber, a professor of theology. Weber learned Latin in secondary school, and began to study medicine in 1811 at the University of Wittenberg. He received his doctor of medicine degree in 1815, specializing in comparative anatomy. Weber became a lecturer at the University of Leipzig in 1817 and was promoted to professor of anatomy the following year. He remained at the University of Leipzig until his retirement.

Weber made his name studying touch, pain, sight, hearing, taste, and smell. He was one of the first psychologists to experiment. He did not just sit at a...