from The Century Dictionary and Cyclopedia
- Kidney-shaped; reniform; in botany, resembling the genus Nephrodium.
- n. In mathematics, a curve of the sixth order with one triple and one single crunode, the polar equation being r = a (1 + 2 sin ½θ).
Sorry, no etymologies found.
To the right you see an ordinary nephroid lurking in a coffee cup.
You know the ordinary nephroid as the reflected catacaustic of a circle, the involute of Caley’s sextic, and a generally good-natured two-cusped epicycloid.
But Freeth’s nephroid is something altogether different: a strophoid of a circle with a double curlicue in the kidney crotch.
T.J. Freeth 1819-1904, our firm’s founder, was unavailable when the photographer came around, but this is his nephroid.