Descartes’ insightful derivation of Snell’s law is translated into English and seen to be largely equivalent to the mechanical-particle or corpuscular derivation often attributed to Newton (who was seven years old at Descartes’ death). Such mechanical theories of refraction are now widely held to yield unphysical results for light, and thus to constitute clear evidence that light cannot consist of classical particles, and must therefore be classical waves or else a quantum-mechanical phenomenon. We show that this evidence is illusory and derives only from confusion of momentum with velocity. An alternate operational formulation of the law of refraction, which applies to any type of reversibly propagating energy, including light and material particles, is summarized. It thus follows that the principal modern reason for rejecting a classical-particle or corpuscular description of light (speed change upon refraction) is unfounded and that such a description is actually possible and useful.
© 1976 Optical Society of America
W. B. Joyce and Alice Joyce, "Descartes, Newton, and Snell’s law," J. Opt. Soc. Am. 66, 1-8 (1976)