1795–1878 · anatomist and physiologist, Leipzig

rnst Heinrich Weber spent his working life at the University of Leipzig as a professor of anatomy and then physiology. He is remembered for careful experiments on the sense of touch, and for one regularity that turned out to be very general.

what he did

Weber measured how far apart two points on the skin must be before they are felt as two, and found the distance varies enormously over the body: small on the fingertips and lips, large on the back. He also asked people to compare weights. The smallest difference they could detect was not a fixed amount but a roughly fixed proportion of the weight they started with. He published this work in Latin in 1834 (Weber, 1834) and in a longer German treatment of touch in 1846.

That proportion is now the Weber fraction, and the observation that it stays roughly constant is Weber's law. The name was given by Fechner, his Leipzig colleague, who made the law the foundation of psychophysics (Fechner, 1860).

Weber's law, in one line. If you can just tell 100 grams from 103 grams, you should just tell 200 from about 206. The just-noticeable difference grows with the starting weight; the ratio stays near the same. It holds best in the middle of a sense's range and fails near its edges.

why it matters

Weber showed that a mental quantity, the smallest difference you can notice, could be measured and would obey a simple rule. That is the first step from philosophy of the senses to experimental psychology. With his brother Eduard he also showed that stimulating the vagus nerve slows the heart, an early demonstration of nervous inhibition.

The tour has a psychology hall with portraits on the walls; the frames there belong to the tour's own story. The plain tour lists them.

Primary works and sources

1. Weber (1834). De pulsu, resorptione, auditu et tactu: annotationes anatomicae et physiologicae. Leipzig: Koehler.
2. Fechner (1860). Elemente der Psychophysik. Leipzig: Breitkopf und Härtel.

Try it yourself. [playful] Small toys on the toy shelf that show this in action:   • the line judge — find your Weber fraction for line length

see also

	Fechner — who named the law and built on it
	timeline: psychophysics — from 1834
	glossary: Weber fraction — and JND