Bean machine

Bean machine

The Bean Machine, also known as the Quincunx, is a device invented by Sir Francis Galton to demonstrate the law of error and the normal distribution.

The machine consists of a vertical board with interleaved rows of pins. Balls are dropped from the top, and bounce randomly left and right as they hit the pins. Eventually, they are collected into one-ball-wide bins at the bottom. The height of ball columns in the bins approximates a bell curve.

External links

Simulation of the bean machine at RAND http://www.rand.org/methodology/stat/applets/clt.html

A longer article on Sir Francis Galton and the bean machine http://www.maps.jcu.edu.au/hist/stats/galton/galton16.htm

Another simulation, with explanations, by prof. Mai Zhou http://www.ms.uky.edu/~mai/java/stat/GaltonMachine.html

Yet another simulation, from John Carroll University http://www.jcu.edu/math/isep/Quincunx/Quincunx.html