A parallel beam of light falls normally on the first face of a prism of a small angle. At the second face it is partly transmitted and partly reflected. The reflected beam striking at the first face again emerges from it in a direction making an angle of 6∘30′ with the reversed direction of the incident beam. The refracted beam is found to have undergone a deviation of 1∘15′ from the original direction. Calculate the refractive index of the glass and the angle of the prism.