Silvered-glass mirror and the Foucault test
Espejo de vidrio plateado y prueba de Foucault
- Date
- 1857-1858 · confidence high
- Place
- Paris, France
- Credited to
- Léon Foucault
- Field
- Communication
What it is
Foucault replaces the metal mirror with a glass one coated with silver, much lighter and easier to polish, and devises the knife-edge test to measure its flaws. It made the modern reflecting telescope possible.
Silver on glass was due to Liebig (1835), and Steinheil applied it to telescope mirrors in 1856; Foucault perfected it and created the test method.
What it led to
- the great astronomical reflectors of the 20th century
- amateur astronomy with home-made mirrors
- optical surface metrology