Philosophiæ Naturalis Principia Mathematica
In his "Philosophiæ Naturalis Principia Mathematica", Isaac Newton (1687) presents a disproof of Descartes' vortex theory of the motion of the planets. In his "Opticks", Newton describes an optical "experimentum crucis" in the "First Book, Part I, Proposition II, Theorem II, Experiment 6", to prove that sunlight consists of rays that differ in their index of refraction.