Hero's Catoptrics: reflection follows the shortest path
Catóptrica de Herón: la reflexión sigue el camino más corto
- Date
- c. 60 · confidence low
- Place
- Alexandria, Egypt
- Credited to
- Hero of Alexandria
- Field
- Communication
⚠️ Disputed: the sources disagree.
What was discovered
Hero shows that the angle of incidence equals the angle of reflection because the light then travels the shortest path between object and eye. It is the first extremal principle in physics.
The Catoptrics survives only in Latin and was attributed to Ptolemy for centuries; it is now usually given to Hero, but authorship and date remain debated.
What it led to
- Alhazen's least-path reasoning
- Fermat's principle of least time
- a view of nature governed by principles of economy