# Steiner's Porism

Start with two fixed circles, one inside the other, but not necessarily right in the center of the
other. Place a circle between and touching the two circles. Place another between and touching the
two circles but also touching the circle you just placed. Repeat. Eventually, your circles will go
all the way around the ring. In some instances, the last circle you placed will just touch the first
circle. Steiner's Porism says that if that occurs, then it doesn't matter where you put the first
circle; the last will always touch the first.

This figure utilizes the Geometry Applet.

March, 1996.

David E. Joyce

Department of Mathematics and Computer Science

Clark University

Worcester, MA 01610

The address of this file is http://aleph0.clarku.edu/~djoyce/java/Geometry/steiner.html