Freeth, Rev. T. J. May 8, 1878 communication to the London Math. Soc. referenced as "The Nephroid, Heptagon, &c." Proc.
London. Math. Soc.10, p. 130, 1878. The curve is explicitly described
in the Appendix of vol. 10 on p. 228.Lawrence, J. D.
A
Catalog of Special Plane Curves. New York: Dover, pp. 175 and 177-178,
1972.MacTutor History of Mathematics Archive. "Freeth's Nephroid."
http://www-groups.dcs.st-and.ac.uk/~history/Curves/Freeths.html.Sloane,
N. J. A. Sequences A138498 in "The
On-Line Encyclopedia of Integer Sequences."