# The Dictionary of Mathematical Eponymy: Borromean rings and the Clélie curve

*I’m cheating a bit with this one; the Borromean rings are named after the whole of the Borromeo family, and the Clélie curve is (unusually) named after a mathematician’s first name. But this is my dictionary, and I’m going to claim a twofer here.*

### Who was Clelia Grillo Borromeo?

Clelia (or Celia) Grillo Borromeo (1684-1777) was a Genovese scientist and mathematician. The daughter of a duke, she spoke eight languages and was described as an ‘independent’ person, which was an eccentric attribute for a woman of her time.

She died in Milan in 1777.

### What are the Borromean rings?

The Borromean rings are one of my favourite mathematical objects: three rings that interlock in such a way that removing any one of them causes the other two to fall apart. They’re named for the aristocratic Borromeo family, but have a much longer history: Norse image stones show a topologically equivalent *valknut*, made of three equilateral triangles, as early as the 7th century.

### What is a Clélie curve?

A *Clélie* is a curve on a sphere whose longitude ($\phi$) and colatitude ($\theta$) are connected by the equation $\phi = c \theta$ for $c > 0$.

The curve traces out a spiral on the spherical surface. It’s neat!

### Why is it important?

A Clélie describes the motion of a satellite that passes over the Earth’s poles. Plus, they’re pretty neat!