How do the refractive indices of air water and glass compare?

The refractive index ($n$) of a substance is a measure of how much it slows the speed of light compared to a vacuum, defined by the ratio $n=c/v$. When comparing air, water, and glass, the refractive index increases as the medium becomes denser:12

• Air: Has a refractive index of approximately 1.0003.12
• Water: Has a higher refractive index of approximately 1.333.1
• Glass: Has a significantly higher refractive index, typically ranging from 1.5 to 1.655 depending on the type (e.g., crown glass is 1.517, while dense flint glass is 1.655).12

Because the refractive index is a measure of how light is bent when passing between media, light traveling from air into water, or from water into glass, will bend toward the normal line because it is entering a medium with a higher refractive index. Conversely, the path of light is reversible, meaning it bends away from the normal when moving from a medium of higher refractive index to one of lower refractive index.13