The underlying index varies in different countries.

These particles make the refractive index of the air vary with height abnormally.

Hymnal indexes vary in alphabetizing him under 'G' or 'P'.

Their refractive index, for example, may vary depending on direction.

The refractive index of the extraordinary ray varies depending on its direction.

The refractive index of a certain sample varies for nearly all materials for different wavelengths.

The index varies from zero to 1.

Refractive index of materials varies with the wavelength.

The refractive index of materials varies with the wavelength (and frequency) of light.

To finish the story, Poincaré states that the index of refraction will also vary with the distance r, in inverse proportion to .