In his 1678 `` Traité de la Lumière '' , Christiaan Huygens showed how Snell 's law of sines could be explained by , or derived from , the wave nature of light , using what we have come to call the Huygens -- Fresnel principle .
In `` Traité de la Lumiere '' , 1678 , Huygens showed how Snell 's law of sines could be explained by , or derived from , the wave nature of light .