A new method is reported to find the refractive index (n) of prism materials by measuring only the angle of incidence (i) when the emergent ray grazes the surface at which refraction takes place. A new general equation is obtained at this grazing emergence situation. Different equations have also been derived for the dependence of n on i for ( 30º - 60º - 90º), ( 45º - 45º - 90º) and ( 60º - 60º - 60º) prisms and accurate values have been found. The limit of applications of those equations are examined and tested.
