A parallel light beam containing two wavelengths, 480 nm and 700 nm, strikes a plain piece of glass at an angle of incidence of 60e. The index of refraction of the glass is 1.4830 at 480 nm and 1.4760 at 700 nm. Determine the angle between the two beams in the glass.

Huygen's principle: Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all the wavelets - that is, tangent to all of them.