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Salmon's Theorem

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.


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

© 1996-9 Eric W. Weisstein