A direct-vision prism is made out of three prisms, each with a refracting angle of $\mathrm{\theta }={60}^{\circ }$, attached to each other as shown in the figure. Light of a certain wavelength is incident on the first prism, The angle of incidence is 30⁰ and the ray leaves the third prism parallel to the direction of incidence. The refractive index of the glass of the first and third prisms is 1.5. Find the refractive index of the material of the middle prism. $(\sqrt{6}=2.45)$