What sort of arrangement is to be taken so that an object cannot be visible even in light?
Or, why is a piece of glass immersed in glycerin not visible?

Explanation

An object having nearly the same refractive index as the medium will not be visible in that medium. Since the refractive indices of both of them are nearly the same, reflection or refraction of visible ray almost does not take place at their surface of separation and light will travel almost undeviated through them. Then in cannot be understood that light in traveling from one medium to another. It seems as if light is moving in the same medium. As a result, the surface of separation is not visible. So a medium vanishes in the other medium.
The refractive indices of glycerine and glass are almost equal. So when a piece of glass is immersed in glycerine kept in a vessel, the piece of glass in not visible.