A direct vision spectroscope has been designed to obtain dispersion...

A direct vision spectroscope has been designed to obtain dispersion without deviation by arranging alternate inverted thin prisms of crown glass (refractive index $\mu_1=\sqrt{2}$ ) and flint glass $\left(\mu_2=\sqrt{3}\right)$ with refracting angle $\theta_{\text {fint }}=3^{{}^{{}^{\circ}}}$. The refracting angle $\theta_{\text {crown }}$ of the crown glass prism is