The retardation of a uniaxial negative mineral of thickness 0.03 mm is 0.05160 mm in its principal section of indicatrix. if the refractive index corresponding

The retardation of a uniaxial negative mineral of thickness 0.03 mm is 0.05160 mm in its principal section of indicatrix. If the refractive index corresponding to the E-ray is 1.486, the value of the refractive index (correct to three decimal places) of the O-ray is