The envelope of refracted rays for a given curve.
Diacaustic
See also
Catacaustic, CausticExplore with Wolfram|Alpha
References
Lawrence, J. D. A Catalog of Special Plane Curves. New York: Dover, p. 60, 1972.Referenced on Wolfram|Alpha
DiacausticCite this as:
Weisstein, Eric W. "Diacaustic." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Diacaustic.html