Willebrord Snell

Mathematician and astronomer — Willebrord Snell (Leiden, 1580 – Leiden, 1626) was a Dutch mathematician and astronomer, professor at the University of Leiden. He is best known for the law describing the refraction of light passing between two transparent media, formulated around 1621: it relates the angles of incidence and refraction to the refractive indices of the materials and is one of the pillars of geometrical optics. Snell also made an important contribution to geodesy, developing a triangulation method to measure the Earth’s circumference from a network of triangles. His work on refraction, unpublished during his lifetime, was made known after his death.

Trivia

The law of refraction had actually been discovered centuries earlier by the Arab scholar Ibn Sahl and later reformulated by Descartes; for this reason it is called the ‘law of Descartes’ in France, while in the English-speaking world it bears Snell’s name.

Theories and contributions

• Snell’s law (refraction) — When light passes between two media, $n_1 \sin\theta_1 = n_2 \sin\theta_2$, where $n$ is the refractive index.
• Geodetic triangulation — Method for measuring large distances and the Earth’s radius using networks of triangles with measured angles.

Featured in chapters

16 Z

Linked atoms

3 linked atoms.

16 Onde

• Refraction and Snell’s law
• The light ray

Z Appendice — Maturità

• Key formulas — Waves and optics