In sentence

> 
> They were rescued by Joseph-Louis Liouville, the son of a captain in Napoleon's army who became a professor in the Collège de France.
> 
> 
> 

who became a professor: Joseph or his father?

Photo of the source:
[![enter image description here](https://i.stack.imgur.com/dyLpA.jpg)](https://i.stack.imgur.com/dyLpA.jpg)
Why beauty is truth: a history of symmetry / Ian Stewart. ISBN-13: 978-0-465-08236-0