Poinsot's spirals

In mathematics, Poinsot's spirals are two spirals represented by the polar equations


 * $$ r = a\ \operatorname{csch} (n\theta) $$
 * $$ r = a\ \operatorname{sech} (n\theta) $$

where csch is the hyperbolic cosecant, and sech is the hyperbolic secant. They are named after the French mathematician Louis Poinsot.