Huygens' methods for determining optical parameters in birefringence (Q860126)

The author gives a new critical discussion, based on Huygens' notebooks, of the methods that Huygens used to construct the decomposition of a ray of light into two rays (birefringence) when it passes through an anisotropic crystal. The main question is how Huygens combined measurements with mathematics. One conclusion is that Huygens made a lot of measurements but in the end settled on the one number that was best in accordance with his theory. Huygens results were eventually printed in his ``Traité de la Lumière'' of 1690.