Cayley's Sextic Evolute

$\begin{figure}\begin{center}\BoxedEPSF{CayleysSexticEvolute.epsf scaled 800}\end{center}\end{figure}$

The Evolute of Cayley's sextic is

$\begin{eqnarray*} x&=&{\textstyle{1\over 8}}a+{\textstyle{1\over 16}}a[3\cos({\... ...textstyle{1\over 16}}a[3\sin({\textstyle{2\over 3}}t)-\sin(2t)], \end{eqnarray*}$

which is a Nephroid.