# Snell-Descartes Law/Historical Note

## Historical Note on Snell-Descartes Law

Willebrord van Royen Snell made his discovery in $1621$.

René Descartes was first to publish it, which he did in $1637$. Snell's own work did not appear until $1703$ when Christiaan Huygens included it in his Dioptrica.

However, it appears that Descartes' own statement was stated incorrectly as $\dfrac {\sin \alpha_1} {\sin \alpha_2} = \dfrac {v_2} {v_1}$, and proved inadequately.

It may well indeed be that Descartes himself learned it from Snell, who now generally holds the credit for its discovery.

It needs to be noted that this law had previously been discovered by several other scientists, including Ibn Sahl in $984$ and Thomas Harriot in $1602$.

In France this law is called la loi de Descartes or loi de Snell-Descartes, while elsewhere it tends to be known as Snell's law, or Snell's Law of Refraction.