Huygens' principle tells us that a wavefront can be created between two or more in-phase waves perpendicularly to the direction they are traveling. Spherical wavelets can then be considered to be expanding from any number of points on this wavefront. Finally, a new wavefront that predicts the...
of light is that of the least optical path,then the phase difference between them is zeroan()dr,where n)is the local index of re-fraction,and readily gives the laws of reflectionand refraction between two media.In its mostParis-[ko m sin(0 )dx+=0(1)general form,Fermat's principle ...