Given a track bounded by two confocal Ellipses, if a ball is rolled so that its trajectory is tangent to the inner Ellipse, the ball's trajectory will be tangent to the inner Ellipse following all subsequent caroms as well.

**References**

Salmon, G. *A Treatise on Conic Sections.* New York: Chelsea, p. 182, 1954.

© 1996-9

1999-05-26