Who made first the connection between light rays and wave fronts?
The fact is stated in many places, e.g., wikipedia, but I couldn't find a history.
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Paragraph 2 of Did Hamilton anticipate quantum mechanics?
"In a simple form the analogy was discovered by Huygens around 1670 (published in Traitė de la Lumiere, 1678), who noticed that propagation of waves could be dually described in terms of wavefronts and rays ("characteristics") perpendicular to them. The latter can be considered as trajectories of particles, and massive amounts of particles spreading along characteristics can create the appearence of a continuous wave. But it also works vise versa, and Huygens suggested that light may well be a wave, with geometric optics of rays being only the first approximation. In particular, Hyugens showed how Fermat's least time principle follows from the analogy, Johann Bernoulli used it to solve the famous brachistochrone problem in 1696, and in 1818 Fresnel showed how not only geometric optics and also diffraction and interference can be explained by wave optics, which led to its wide acceptance."