Convex lens / reading stone
Lente convexa y piedra de lectura
- Date
- c. 1021 · confidence low
- Place
- Cairo, Egypt (Alhazen); Europe (Roger Bacon, 1267)
- Credited to
- Ibn al-Haytham (theory); European monks (reading stones)
- People
- 👤 Alhacén965–1038
- Field
- Communication
⚠️ Disputed: the sources disagree.
What it is
A segment of a glass or beryl sphere that magnifies writing when laid upon it, the theory of whose refraction Alhazen set out. The first practical use of magnifying optics.
Lenses had existed in antiquity as curiosities; the shift to usable reading lenses took place between 1021 (Alhazen) and c. 1270 (Bacon, reading stones).
What it led to
- eyeglasses and precision optics
- the theory of vision and refraction in Bacon, Witelo and Pecham
- the instrumental correction of the senses as a scientific principle
Built on
- Nimrud lens (rock-crystal disc)c. 700 BCE
- Ptolemy's Optics: measuring angles of refractionc. 150
- Nimrud lens and ancient crystal spheres