Christiaan Huygens’s Treatise on Light (1690) proposed what Newton’s authority would bury for a century: that light is a wave. Here is the celebrated principle — every point of a wavefront the source of new wavelets — put to work explaining reflection, refraction, and the strange double refraction of Iceland spar.
When Young and Fresnel finally vindicated the wave theory, this was the book they vindicated. Download the free EPUB and read physics’ greatest delayed triumph in the original argument.