Snell’s Law of Refraction

The ratio to the sine of the angle of incidence to the sine of angle of refraction is a constant quantity for any two given media. 

  sin i

   ———  = n 

       sin r

where n is called the refractive index of the second medium with respect to the first medium.

Since angle of incidence is greater than the angle of refraction, hence indices of all matter than air will be more than one.

 Refractive index of water is 1.3, of glass 1.5, of cornea 1.3, of lens in the eye 1.42, of crown glass 1.5, Titan lens (SP1) 1.7 and that of diamond is 2.5, being the highest.